Proceedings




DRY BEAN TOLERANCE TO HALOSULFURON APPLIED POSTEMERGENCE. N. Soltani*1, R. E. Nurse2, C. Shropshire1, P. H. Sikkema1; 1University of Guelph, Ridgetown, ON, 2Agriculture and Agri-Food Canada, Harrow, ON (1)

ABSTRACT

Four field trials were conducted over a two-year period (2009 and 2010) at Exeter and Ridgetown, Ontario to evaluate the tolerance of adzuki (‘Erimo’), black (‘Black Velvet’), cranberry (‘Etna’), kidney (‘Red Hawk’), otebo (‘Hime’), pinto (‘Wind Breaker’), Small Red Mexican (‘Merlot’) and white (‘T9905’) beans to halosulfuron applied postemergence (POST) at 35 and 70 g ai ha-1. All treatments including the non-treated control were maintained weed free during the growing season. Halosulfuron applied POST caused as much as 73, 7, 13, 12, 12, 11, 11 and 9% injury in adzuki, black, cranberry, kidney, otebo, pinto, Small Red Mexican (SRM) and white beans, respectively. Halosulfuron applied POST reduced adzuki bean height as much as 52 and 70% at Exeter and Ridgetown, respectively. Plant height was not affected in the other market classes of dry bean evaluated. Halosulfuron POST reduced shoot dry weight of adzuki bean 68% at both rates evaluated. Otebo and SRM bean shoot dry weight were not affected when halosulfuron was applied POST at 35 g ai ha-1 but otebo bean shoot dry weight was reduced 12% and SRM bean shoot dry weight was reduced 14% at 70 g ai ha-1. Shoot dry weight of black, cranberry, kidney, pinto and white bean was not affected with either rate of halosulfuron. Halosulfuron applied POST resulted in a delay in maturity of adzuki, cranberry and kidney bean but the maturity of the other market classes was not affected. Seed yield of adzuki bean was decreased 58% at 35 g ai ha-1 and 68% at 70 g ai ha-1 with halosulfuron. White bean yield was not affected with halosulfuron applied POST at 35 g ai ha-1 but was reduced 9% at 70 g ai ha-1. Seed yield of black, cranberry, kidney, otebo, pinto and SRM bean was not reduced with either rate of halosulfuron.




EVALUATION OF HERBICIDES TO CONTROL SUSPECTED ALS RESISTANT SOLANUM PTYCANTHUM. K. M. Vollmer*1, H. Wilson2, T. Hines2; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Painter, VA (2)

ABSTRACT

 

Eastern black nightshade (Solanum ptycanthum) is a problem in several crops on Virginia’s Eastern Shore including corn, soybean, and tomato.   Most growers on the Eastern Shore utilize no-till practices which rely heavily on herbicides for weed control. ALS-inhibiting herbicides such as chlorimuron and thifensulfuron have been heavily relied upon, and repeated applications have led to their reduced effectiveness against eastern black nightshade. In the summer of 2010 a field trial was established in a corn field in Eastville, VA. Plots were 6.7 ft x 20 ft and consisted of 4 replications per treatment. The following herbicides were applied POST before the V6 growth stage: bromoxynil (0.019 lb ai/A), dicamba (0.5 lb ai/A)+ NIS (0.25%) + UAN (1.25% v/v), nicosulfuron (0.031lb ai/A) + NIS (0.25%) + 30% N (0.25%) , nicosulfuron (0.023 lb ai/A) + rimsulfuron (0.012 lb ai/a) + COC (1% ) + 30% N (0.25%), rimsulfuron (0.0143 lb ai/A) + thifensulfuron (0.00313 lb ai/A) + isoxadifen-ethyl (0.0072 lb ai/A) + NIS (0.25%) + 30% N (0.25% ), acetochlor (1.2 lb ai/A) + glyphosate (0.75 lb ai/A) + NIS (0.25%), and glyphosate (0.75 lb ai/A). Plots were visually evaluated for % control and % injury 7, 14, and 21 days after treatment. There was no visible injury to the crop throughout the growing season. Glyphosate alone provided 85% control 2 WAT, but declined 3 WAT. The acetochlor + glyphosate mix resulted in 95 and 90 percent control two and three weeks after treatment, respectively.  Dicamba provided over 57 and 69% control 2 and 3 WAT respectively. Even though injury symptoms were observed with the ALS inhibiting herbicides, all provided less than 25% control of eastern black nightshade.   This leads us to believe that eastern black nightshade is resistant or at least tolerant to ALS inhibiting herbicides, and that tank mixes of glyphosate + actetochlor may provide a viable alternative to these herbicides. 

 


CURRENT STATUS OF WEED INFESTATION IN SOYBEAN RR IN PARANA STATE, IN SOUTHERN BRAZIL. F. S. Adegas*, D. Gazziero, E. Voll; Embrapa, Londrina, Brazil (3)

ABSTRACT

Soybean is the main agricultural crop in Brazil, with 23.2 million hectares grown last season (2009/10). Parana State, located in the south, is the second largest producer in the country, with 4.3 million ha. Since the release of the planting of RR soybeans in 2005, Embrapa Soybean has been doing annual monitoring of the situation of RR soybeans in Parana, which last season took 66% of the area, similar to the national average which was 68%. The average number of glyphosate applications has remained stable, being 2.4 per property in the last season. However, the doses of glyphosate per unit area has increased from 828 g ae/ha in 2005/06 to 1717 g ae/ha in 2009/10. There was also a large increase in the addition of other herbicides to glyphosate, which in 2005/06 was 10.6% against 81.3% achieved last season. Currently, the main weeds tolerant to glyphosate in percentage of presence in Parana’s areas are Commelina benghalensis (85%), Ipomea sp. (83%), Conyza sp. (81%), Richardia brasiliensis (48%), Digitaria insularis (25%), and Chamaesyce hirta (22%). Four cases of glyphosate-resistant weeds have been registered in Paraná : Conyza bonariensis, Conyza canadensis, Digitaria insularis, and Lolium multiflorum.




CARRYOVER POTENTIAL OF HERBICIDES USED FOR CONYZA SP. CONTROL. D. G. Alonso*1, J. Constantin1, R. S. Oliveira Jr.1, W. C. Koskinen2, A. Oliveira Neto1, H. A. Dan1, N. Guerra1; 1Universidade Estadual de Maringá, Maringá, Brazil, 2USDA-ARS/University of Minnesota, St. Paul, MN (4)

ABSTRACT

Conyza spp. is one of the most important weeds in southern Brazil, and has imposed a serious threat to agriculture as the selection of tolerant and resistant biotypes to glyphosate increases. This, in turn, has led to continuous efforts by researchers for management alternatives for this species. This weed’s main emergence flux is in winter, therefore, different winter burndown alternatives have been studied for Conyza biotypes using tank mixtures of glyphosate+2,4-D, with or not with residual soil herbicides. Research was conducted to evaluate soil carryover of residual herbicides that can be used for Conyza winter control. Greenhouse experiments were carried out in pots arranged in a complete randomized block design with 6 replications. Soil used in these experiments had 23% sand, 72% clay, and 4.89 g dm-3 OC. Herbicides evaluated in this experiment were metsulfuron (3.6 g ha-1), amicarbazone (420 g ha-1), metribuzin (480 g ha-1), isoxaflutole (56.25 g ha-1), and MSMA (2370 g ha-1). Treatments consisted of soybean sowing (six seeds/pot) at 0, 30, 60, 90, and 120 days after herbicide application (DAA), and soil cover with oat straw (simulating no tillage with straw at 3.5 ton ha-1) or no cover. During this period soil moisture was maintained by simulating the average historic precipitation for in winter months (June, July, August, and September) in Maringá, Brazil. The only herbicide that killed soybean plants was amicarbazone, either when applied to soil with (up to 60 DAA) or without (up to 120 DAA) straw. All other herbicides affected growth to some extent. Metribuzin only caused damage when soybean was sowed just after application on covered soil, and until 30 DAA on noncovered soil. Metsulfuron caused shoot dry biomass reduction when sowing was carried out at 60 DAA for both soil treatments. Isoxaflutole affected growth up to 60 DAA in straw covered soil, and 90 DAA for soil without cover. MSMA did not cause negative effects when applied on soil with cover, but caused shoot dry biomass reduction up to 90 DAA on soil without cover. The results suggest that in most cases soil cover decrease the carryover effect. To avoid soybean injury, it is suggested that sowing should be done 90 DAA for MSMA and metsulfuron, and 120 DAA for isoxaflutole and metribuzin. For amicarbazone, a significant carryover effect was found even when soybean was sown 120 DAA.



FOUR YEARS OF DICAMBA-TOLERANT SOYBEANS IN KENTUCKY. S. Carter*1, C. Slack1, S. Seifert-Higgins2; 1University of Kentucky, Lexington, KY, 2Monsanto Company, St. Louis, MO (5)

ABSTRACT

From 2007 through 2010, the University of Kentucky has conducted annual field trials examining weed control options for soybeans with dicamba and glyphosate tolerance.  Each trial contained varying rates of dicamba in combination with glyphosate, glyphosate alone, and a comparative treatment. Weed species rated varied from year to year but included giant ragweed, velvetleaf, smooth pigweed, morning glory and giant foxtail.  In 2007, weed control ratings following the final application achieved ≥96% control of all species observed and no crop injury.  In 2008, the pattern followed that of 2007 where all weed species rated following the final application reached ≥93% control with no crop injury observed.  In 2009, all treatments were mimicked from the previous two studies. Weed control ratings following the final application were consistent with previous data by which all species achieved ≥96% control and no significant crop injury.  In 2010, treatments were changed to accommodate postemergence applications of dicamba mixed with glyphosate, with varying rates of dicamba. Some treatments followed a preemergence application of flumioxazin. Weed control ratings after the second postemergence application reached 99% and no crop injury was observed.




SOYBEAN SPACING AND GROWING HABIT AND ITS RELATIONSHIP WITH WEED COMPETITION. F. S. Adegas*, D. Gazziero, E. Voll; Embrapa, Londrina, Brazil (6)

ABSTRACT




CONFIRMATION OF GLYPHOSATE-RESISTANT CONYZA CANADENSIS IN OKLAHOMA. J. Armstrong*; Oklahoma State University, Stillwater, OK (7)

ABSTRACT

Marestail (Conyza canadensis) is an increasingly difficult weed to control in Oklahoma due to the increase in adoption of reduced-tillage production practices and reliance on glyphosate for preplant and in-season weed control. While glyphosate-resistant marestail is a significant problem in many parts of the United States, the presence of glyphosate-resistant marestail has not previously been confirmed in Oklahoma.  In 2009 and 2010, composite samples of 31 marestail populations were collected from fields in 11 counties when marestail had reached maturity.  Of the 31 collected populations, 18 were successfully grown in the greenhouse and screened with glyphosate at doses of 0.84 kg ae/ha, 1.68 kg ae, and 3.36 kg ae.  Based on visual estimates of weed control taken at four weeks after treatment, 9 of the 18 populations were controlled at 50% or less compared to a known susceptible sample at the 1.68 kg ae dose.  With the exception of one population collected in 2010, all marestail populations were controlled at greater than 50% at the 3.36 kg ae dose of glyphosate.  Results from this survey and screening trial confirm the presence of glyphosate-resistant marestail in Oklahoma.  




SUSCEPTIBLE WILD OAT (AVENA FATUA) ENDANGERED IN MANITOBA. H. J. Beckie*, C. Lozinski, S. Shirriff; Agriculture and Agri-Food Canada, Saskatoon, SK (8)

ABSTRACT

A survey of weeds resistant to herbicides in 300 randomly selected fields was conducted across the major agricultural ecoregions of Manitoba in 2008. All residual weed species with mature seeds were mapped and sampled before harvest. Selected fields were cropped to cereals, oilseeds, or pulses. Samples of weed species were subsequently screened in the greenhouse with herbicides with different modes of action. Herein, we summarize results of group 1 (ACCase inhibitor) and group 2 (ALS inhibitor) testing. Of 198 fields where wild oat samples were collected, 62% had a herbicide-resistant population: group 1, 55% (vs. 40% in 2002); group 2, 18% (vs. 13% in 2002); group 8, 11% (not tested in 2002); group 1 and 2, 13% (vs. 8% in 2002); group 1 and 8, 8%; group 2 and 8, 5%; and group 1 and 2 and 8, 4%.  Therefore, just over one-third of fields with wild oat in Manitoba have herbicide-susceptible populations. Of 91 fields where green foxtail [Setaria viridis (L.) Beauv.] samples were collected, 44% had a group 1-resistant population. The incidence of group 1 resistance in green foxtail has doubled in six years; in the 2002 survey, 22% of fields with green foxtail had a herbicide-resistant population. Incidence of group 2 resistance in broadleaf weed species was low, with a single resistant population of chickweed [Stellaria media (L.) Vill.], cleavers (Galium aparine L.), and wild mustard (Sinapis arvensis L.). The results of this survey highlight the continuing rapid decline in field frequency of herbicide-susceptible wild oat and green foxtail, the two most abundant weeds in Manitoba.




MULTIPLE HERBICIDE-RESISTANT SAGITTARIA MONTEVIDENSIS POPULATION IN SANTA CATARINA STATE (BRAZIL) RICE FIELDS. D. S. Eberhardt, J. A. Noldin*; Epagri, Itajai, Brazil (9)

ABSTRACT

Multiple Herbicide-Resistant Sagittaria montevidensis Population in Santa Catarina State (Brazil) Rice Fields 

 

Domingos S. Eberhardt, José A. Noldin

Epagri/Estação Experimental de Itajaí, Brazil.

Sagittaria montevidensis
(SAGMO) is a troublesome weed in irrigated rice areas in Santa Catarina. In the 1990’s, this weed was already disseminated in the rice fields and easily controlled with acetolactate synthase (ALS) inhibitors herbicides. The first case of SAGMO resistant to ALS herbicide was reported in 1999 and the best control option for these populations was bentazon, a photosystem II (PS II) inhibitor herbicide. In the last decade, bentazon became the main and almost the only option to control SAGMO and was used in more than 80% of the paddy rice areas. In 2008, a rice farmer from Ilhota County in the Itajai Valey, firstly reported problems to control SAGMO with bentazon, even using high rates. Field experiments were carried out in the 2008/09 and 2009/10 crop seasons at the farmer rice area to evaluate the sensitivity of the local SAGMO population to bentazon as well as to find alternatives to control these populations. Two experiments were also carried out under controlled conditions in 2009 and 2010 to confirm the multiple resistance of SAGMO populations to ALS and PS II herbicides (bentazon). In both experiments the herbicides (penoxsulam, pyrazosulfuron-ethyl, imazapic+imazethapyr and bentazon were evaluated  at 0.5, 1, 2, 4 and 8 times the label rate. In the first field study (2008/09), the maximum control level with bentazon was 50% and 75%, respectively at 1 and 2X the label rate. The tank mixture of bentazon with other herbicides did not improve the efficacy. In the second field experiment (2009/10), bentazon applied at  4X rate controlled 78% (maximum) of SAGMO population, showing resistance of the population to bentazon. The maximum SAGMO control percentage using ALS inhibitors at 4X rate was 43%. The experiments carried out under controlled conditions also resulted in poor control of SAGMO populations. In 2009, SAGMO control with ALS inhibitors was lower than 50% for all herbicides and rates. Bentazon at 1, 4 or 8X rate resulted in 26%, 10% and 1% of surviving plants. In 2010, the percentage of SAGMO surviving plants was 83%, 96%, 71% and 51%, respectively for herbicides penoxsulam, pyrazosulfuron-ethyl, (imazapic+imazethapyr) and bentazon, applied at maximum rate (8X). The higher SAGMO surviving percentages in 2010 was due to the origin of the seeds. In 2009, SAGMO plants were obtained from the seed bank of the farmer area and in 2010, seedlings were established using seeds collected from surviving plants sprayed with bentazon in the year before. The data from these studies confirm the occurrence of SAGMO population cross-resistance to ALS and multiple-resistant to ALS and PS II (bentazon) in rice fields in Santa Catarina, Brazil.



ROW SPACING AND POPULATION EFFECTS IN TWO DRY BEAN CLASSES. R. C. Holmes*, C. L. Sprague; Michigan State University, East Lansing, MI (10)

ABSTRACT

Row Spacing and Population Effects in Two Dry Bean Classes

Ryan C. Holmes, Christy L. Sprague, Graduate Student, Associate Professor, Department of Crop and Soil Sciences, Michigan State University

Dry beans have traditionally been grown in wide rows to allow for inter-row cultivation and harvested using a two step process in which whole plants are pulled from the ground and windrowed, then harvested after allowing the windrows to dry.  The development of new dry bean varieties with a less prostrate growth habit has allowed an increasing percentage of dry beans to be direct harvested without windrowing, but direct harvest is incompatible with traditional inter-row cultivation since cultivation brings rocks to the surface, which interferes with combine operations.  This suggests the need for new weed management strategies while opening the possibility of growing dry beans in narrower rows.  Previous research in other crops has indicated that narrow rows often suppress weeds, and several studies in dry beans have suggested that narrow rows may also improve yield. In order to determine the benefits and limitations of growing dry beans in narrow rows in Michigan, field research was conducted in 2010 at two locations to examine the effect of varying row width and bean populations on: 1) weed suppression, 2) plant architecture, and 3) yield.  Two classes of dry beans were examined, ‘Zorro’ black beans and ‘Merlot’ small red beans.  Both varieties are fairly new and were selected for upright growth.  In addition to class, three factors were examined: row width, population, weed management.  Three row widths were examined at one location: 1) 38 cm, 2) 51 cm, and 3) 76 cm, while at the other location only 38 and 76 cm rows were examined.  Three populations were examined; for black beans, these populations were 1) 196,000 plants per ha, 2) 262,000 plants per ha, and 3) 327,000 plants per ha.  For small red beans, the populations were 1) 148,000 plants per ha, 2) 196,000 plants per ha, and 3) 262,000 plants per ha.  Weed management treatments consisted of weed-free and a POST applied weed control strategy of imazamox + bentazon.  To measure weed suppression, newly emerging weeds were counted several times after the canopy began to form, and weeds were harvested at the end of the season from POST-treated plots, dried, and weighed.  Photosynthetically active radiation was also measured above and below the canopy as it developed to determine light interception by the crop.  To assess plant architecture and yield components, three 0.25 square meter sections of beans were hand harvested from each weed free plot, and number of branches, pods per branch, pods on the main stem, beans per pod, and weight per hundred beans were assessed; also, at one location, maturity was uneven between plots at the end of the season, so this was visually assessed on a 0-100% scale, and lodging was evaluated at both locations on a 0-5 scale. All plots were direct harvested for yield with a combine and adjusted to 18% moisture.  The effect of row width on yield was dependent on environmental conditions and bean class while planting population had little effect on yield.  In the presence of adequate moisture, narrow rows resulted in faster and more complete canopy closure and greater weed suppression.  Small red beans were better competitors with weeds than black beans.  In the presence of a moderate amount of lodging, narrow rows reduced lodging.

 




COMPARISON OF SOYBEAN VARIETIES WITH DIFFERENT HERBICIDE-RESISTANT TRAITS. C. L. Sprague*, G. E. Powell, E. C. Taylor; Michigan State University, East Lansing, MI (11)

ABSTRACT

The 2009 growing season brought about the commercialization of two new herbicide-resistant soybean traits, second generation glyphosate-resistant (Roundup Ready 2 Yield) and glufosinate-resistant (Liberty Link) soybean. There have been claims of increased soybean yield with the second generation glyphosate-resistant soybean technology. Because of these claims seed costs are at a premium. Glufosinate-resistant soybean, on the other hand, provides growers with an additional option for weed control in soybean. In MSU trials we have been able to successfully manage weeds under a number of conditions with this technology. However, there are still a number of questions that growers have about these technologies. Therefore, the objectives of this research were to: 1) evaluate weed control from different weed management systems in glyphosate-resistant (Roundup Ready), Roundup Ready 2 Yield, Liberty Link, and conventional (non-GMO) soybean, 2) compare yield from Roundup Ready, Roundup Ready 2 Yield, Liberty Link, and conventional soybeans under several weed management systems, and 3) determine the economic returns for each soybean trait and weed control system. Field studies were conducted in East Lansing and Richville, MI in 2009 and 2010. Soybeans were planted in 38-cm rows at 70,850 seeds per hectare in mid-May at both locations. The four weed management systems evaluated in this study included: 1) a preemergence (PRE) followed by postemergence (POST) herbicide program, 2) a two pass POST herbicide program, 3) a standard PRE herbicide, and 4) a nontreated control. The two years of this research were quite different. Soybean yields were approximately 1,211 kg/ha lower for the highest yielding soybean varieties at both locations in 2010 as compared with 2009. Rainfall in July and August during pod fill was well below the 30 year average. This also led to lower and more variable yield data. Overall the two herbicide systems, PRE followed by POST and POST followed by POST systems provided excellent weed control, regardless of soybean technology. Additionally, we observed different yield potentials of the four soybean traits with differences in environment. Under a high yielding environment the Liberty Link and Roundup Ready 2 Yield soybean varieties were equivalent, the original Roundup Ready also provided good yields under certain herbicide systems. However, in the lower yielding environments we did not observe a difference in soybean technology. Taking into consideration the current economic conditions, the non-GMO soybean varieties with the lower seed cost and $1.00 selling premium actually provided significant economic returns in 1 of the 4 environments for the standard treatment. Taking into account herbicide costs, the economics favored the non-GMO, Liberty Link and Roundup Ready 2 Yield in 2 of 3 environments. 

 




PEANUT RESPONSE TO FOMESAFEN APPLIED AT DIFFERENT TIMINGS AND RATES. P. A. Dotray*1, W. Grichar2, E. P. Prostko3, J. Ferrell4, D. L. Jordan5, L. V. Gilbert6; 1Texas Tech University, Lubbock, TX, 2Texas AgriLife Research, Beeville, TX, 3University of Georgia, Tifton, GA, 4University of Florida, Gainesville, FL, 5North Carolina State University, Raleigh, NC, 6Texas AgriLife Research, Lubbock, TX (12)

ABSTRACT




HERBICIDE PROGRAMS FOR OPTIMUMŽ GATŽ SOYBEANS. D. W. Saunders*1, S. K. Rick2, K. D. Johnson3; 1DuPont Crop Protection, Johnston, IA, 2DuPont Crop Protection, Waterloo, IL, 3DuPont Crop Protection, Grand Forks, ND (13)

ABSTRACT

Weed control programs designed for use on soybeans containing the Optimum® GAT® trait were evaluated by DuPont, university, and contract investigators in 2009 and 2010.  Integrated herbicide programs making use of preemergence, postemergence, and 2-pass weed control strategies were compared to standard treatments   Data collected from 22 internal DuPont locations in 2009 and 13 locations in 2010 indicate excellent performance of new DuPont™ Diligent™, Traverse™, and Freestyle™ herbicides when compared to standard treatments.  Seed products with the Optimum® GAT® trait will be available for sale pending regulatory approvals and field testing.  New DuPont herbicides for the Optimum® GAT® trait are developmental products for which labels have not yet been filed with the EPA.  david.w.saunders@usa.dupont.com




DICAMBA TOLERANT SOYBEAN IN NEBRASKA NO-TILL PRODUCTION SYSTEMS. M. L. Bernards*1, V. Mannam1, S. Seifert-Higgins2; 1University of Nebraska-Lincoln, Lincoln, NE, 2Monsanto Company, St. Louis, MO (14)

ABSTRACT

No-till soybean production reduces soil erosion, but favors the proliferation of winter annual weeds.  Some farmers delay controlling winter annual weeds until the time of soybean planting or later, but the effect of winter annual weed removal time on soybean yield has not been described.  Horseweed is a winter annual weed that has evolved resistance to glyphosate in many fields. Soybeans genetically engineered to be resistant to dicamba are being developed for commercialization. The ability to use dicamba in soybean will provide an additional tool to manage glyphosate-resistant horseweed and other winter annual weeds.  The objectives of this research were to 1) measure how soybean yield was affected by the removal time of winter annual weeds, and 2) evaluate the use of dicamba for weed management in no-till soybean in Nebraska. In the first study, winter annual weeds were removed November 15, March 15, April 1, April 15, May 1, May 15, June 1 and June 15, and plots were kept weed free after the initial weed removal time. Glyphosate-resistant soybean were planted approximately May 15. The experiment was arranged in a randomized complete block design and was conducted for three years at two locations. Soybean yield for each removal time was plotted as the percent yield of the November 15 removal time.  A log-logistic model was fitted to the data to describe the effect of removal time on soybean yield.  In the second study, dicamba-tolerant soybean was planted May 27 in a no-till field near Lincoln, NE. A preplant application to control winter annual weeds was made May 3 to one set of treatments, and a burndown application was made May 27 to a second set of treatments.  Postemergence applications of glyphosate or glyphosate + dicamba were made June 16 and June 18 when most weeds were 10 cm or less.  Weed control and soybean response were evaluated prior to the postemergence herbicide applications and three weeks after the postemergence treatment.  In the first study, delaying winter annual weed removal until the time of planting reduced yield more than 5% in five of six years. The critical time of winter annual weed removal to protect soybean yield from the 5% threshold ranged from March 20 to May 5, depending on year and location.  In the second study, all winter annual weeds (henbit, field pennycress, and prickly lettuce) except horseweed were controlled by preplant or preemergence burndown herbicide applications. Glyphosate alone or tank-mixed with flumioxazin provided less than 70% control of horseweed, but glyphosate tank-mixed with 2,4-D or dicamba provided greater than 88% control prior to the postemergence herbicide application timing.  The timing of herbicide burndown affected summer annual weed presence at the time of the postemergence herbicide application – control of weeds in the preplant timing treatments was reduced compared to preemergence timing treatments. The burndown application timing also affected soybean height – delaying winter annual weed emergence until planting resulted in soybean that were 10 cm shorter at 48 days after planting. Control of green foxtail, Palmer amaranth, common sunflower, and velvetleaf exceeded 90% three weeks after postemergence treatments for all herbicide treatments.  However, control of horseweed differed among treatments three weeks after postemergence applications.  Horseweed control exceeded 96% when both a burndown and postemergence application of a synthetic auxin herbicide were made.  When only one synthetic auxin herbicide was applied, at either the burndown or postemergence application timing, control was 86-88%.  When no synthetic auxin herbicide was applied, horseweed control was 70%. There was no injury to the dicamba-tolerant soybean from either preemergence or postemergence application of dicamba. The use of dicamba increased control of glyphosate-resistant horseweed. However, based on data from the first study and plant height in the second study we expect that the full benefit of the dicamba-tolerant technology will require that farmers control winter annual weeds in advance of planting to maximize soybean yield potential.




RESPONSE OF GIANT REED TO POSTEMERGENCE SUGARCANE HERBICIDES. D. C. Odero*; University of Florida, Belle Glade, FL (15)

ABSTRACT

Giant reed (Arundo donax L.) has been proposed as a potential feedstock for biofuel production in the marginal sugarcane (Saccharum spp. Hybrids) production region of southern Florida. However, giant reed has a high invasive potential where its cultivation is proposed. A dose-response study was conducted in the greenhouse to determine the response of giant reed to postemergence sugarcane grass herbicides. Giant reed plants were treated with asulam and trifloxysulfuron-sodium at six rates from 0.46 to 14.8 kg ai ha-1 and 0.002 to 0.064 kg ai ha-1, respectively. Plants were harvested at 21 days after treatment, dried and weighed to obtain relative dry weight. Overall, giant reed relative dry weight decreased as rates of either asulam or trifloxysulfuron-sodium increased. Relative dry weight reduction was greater for asulam compared to trifloxysulfuron-sodium treated plants. The rate required to cause 50% response (ED50) for relative dry weight was 0.78 and 0.004 kg ai ha-1 (equivalent to 0.21 and 0.25X rate) for asulam and trifloxysulfuron-sodium, respectively. These results suggest that asulam shows a better potential for use in control of giant reed in sugarcane. Additional field studies will be conducted to corroborate these results.




EFFECTS OF MESOSULFURON ON THE GROWTH OF SIX WINTER WHEAT VARIETIES. M. R. Manuchehri*1, I. C. Burke1, T. Rauch2, D. A. Ball3, D. Thill2; 1Washington State University, Pullman, WA, 2University of Idaho, Moscow, ID, 3Oregon State University, Pendleton, OR (16)

ABSTRACT

Mesosulfuron is a herbicide used to control annual grasses in winter wheat. Mesosulfuron can cause chlorisis and stunting of winter wheat especially under stressful environmental conditions, including wide temperature fluctuations and freezing temperatures. Studies were established in Davenport, Dayton, Fairfield, LaCrosse, and Pullman, WA in 2009 to evaluate early crop growth and development of six winter wheat varieties treated with mesosulfuron applied alone and mesosulfuron applied with bromoxynil plus MCPA in mixture. The experimental design was a randomized complete block, strip plot with four replications. Main plots with six winter wheat varieties (Bauermister, Bruehl, Eddy, Eltan, Madsen, and ORCF-102) and sub-plots were two herbicide treatments (mesosulfuron alone, mesosulfuron with bromoxynil plus MCPA) and a non-treated control. Applications were made to trials in Dayton, Lacrosse, and Pullman, WA on March 26; to the trial in Davenport on April 16 and to the trial in Fairfield on May 20. Five plants were harvested from the nontreated plots of each variety on the day of treatment to determine the above ground dry biomass. Five plants were also harvested from all replicates of each treatment 14 and 21 days after treatment (DAT). Injury ratings were recorded at those intervals. Transient growth inhibition was observed when mesosulfuron was applied to ORCF-102 in Pullman, Eltan in LaCrosse and Pullman, and Eddy in LaCrosse and Dayton. Although injury was observed in Madsen, no significant growth inhibition was observed when that variety was treated with mesosulfuron. When mesosulfuron was applied with bromoxynil plus MCPA, significant injury was observed in all varieties at all locations 21 DAT, except Eltan at Fairfield and Madsen at LaCrosse. Early season injury caused by mesosulfuron appeared to be transient at each location. Of the varieties evaluated, Eltan and Eddy appear most sensitive to early season injury, while Madsen and ORCF-102 were the least sensitive. The observed early season injury did not translate into a consistent yield loss, even when mesosulfuron was applied with bromoxynil plus MCPA. The lack of yield response is likely attributable to moisture received in May and June.

 




MID SEASON CONTROL OF BROWNTOP MILLET IN SOYBEAN. W. Molin*; USDA-ARS, Stoneville, MS (17)

ABSTRACT




TOLERANCE OF WIDESTRIKE COTTON VARIETIES TO GLUFOSINATE. D. M. Dodds*1, L. Barber2, G. D. Collins3, C. L. Main4; 1Mississippi State University, Mississippi State, MS, 2University of Arkansas, Little Rock, AR, 3University of Georgia, Tifton, GA, 4University of Tennessee, Jackson, TN (18)

ABSTRACT

Cotton tolerant to glyphosate is planted on greater than 95% of the acreage in the Mid-South. However, as glyphosate-resistant weed species have emerged and spread throughout the Mid-South and Southeastern United States, growers are continually looking for ways to control these species. In particular, glyphosate-resistant Palmer amaranth has proven to be very problematic due to its competitiveness, rapid growth, prolific seed production, and ability to withstand difficult environmental conditions. One option for control of this, and other weed species, is glufosinate. Glufosinate tolerant cotton varieties are available; however, they are only planted on a small percentage of the acreage in the Mid-South and Southeast. Increasingly, growers in many areas are utilizing cotton varieties containing Widestrike™ technology as these varieties utilize the pat gene as a selectable marker for Widestrike™. The pat gene also confers some level of tolerance to glufosinate herbicide. Previous research indicates that glufosinate may cause visual injury to Widestrike™ cotton; however, yields were unaffected. This research was undertaken to determine the level of tolerance present in Widestrike™ cotton in comparison to Liberty Link® cotton. 

 

Studies were conducted at two locations in Starkville, MS; Jackson, TN, Chic, TN; Marianna, AR; and Plains, GA. Fibermax ‘FM 1773LLB2’ and Phytogen ‘PHY 375 WRF’ were planted at seeding rates determined by local standards. Plots consisted of two rows either 9 or 12 m in length. Glufosinate applications were made at 0.59, 1.19, 1.78, and 2.38 kg ai ha-1 either once or twice using a tractor-mounted compressed air sprayer or a CO2 powered backpack sprayer. Applications were made to one- to three-leaf cotton and/or six- to eight-leaf cotton. Visual injury, growth and development, yield, and fiber quality data were collected. No application rate by number of application interactions were present; therefore, data were pooled over number of applications.

 

Visual injury seven days after the one- to three-leaf application increased significantly as application rate increased. Application of 0.59 kg ai ha-1 resulted in ~15% visual injury whereas application of 2.38 kg ai ha-1 resulted in ~47% visual injury to ‘PHY 375 WRF’. Less than 10% injury was observed at all application rates on ‘FM 1773 LLB2’. Plant height was unaffected by glufosinate application for either variety; however, application rates beyond 1.19 kg ai ha-1 caused significant reductions in the number of plant nodes 14 days after the one- to three-leaf application. Cotton injury on ‘PHY 375 WRF’ seven days after the six- to eight-leaf application also increased as application rate increased. Approximately 6% injury was observed following the 0.59 kg ai ha-1 application compared to 30% visual injury following the 2.38 kg ai ha-1 application. Less than 3% injury was observed on ‘FM 1773 LLB2’ at all application rates. Plant height of ‘FM 1773 LLB2’ 14 days after the six- to eight-leaf application was unaffected by application rate. Plant height of ‘PHY 375 WRF’ was reduced at application rates beyond 1.19 kg ai ha-1. Total plant nodes of either variety were unaffected by application rate of glufosinate. End of season plant height and nodes were also unaffected by glufosinate application rate. Application of glufosinate at rates beyond 1.19 kg ai ha-1 did increase nodes above cracked boll of ‘PHY 375 WRF’ indicating a delay in maturity. Application rate had no effect on maturity of ‘FM 1773 LLB2’. Lint yield of ‘FM 1773 LLB2’ was unaffected by glufosinate application rate. Application rates beyond 1.19 kg ai ha-1 resulted in reduced lint yield of ‘PHY 375 WRF’. 




COMPARISON OF ALION PERFORMANCE BETWEEN FALL OR SPRING APPLICATIONS IN ORCHARDS ACROSS THE UNITED STATES. S. A. Gersdorf*1, D. Unland2, M. Anderson3; 1Bayer CropScience, Monmouth, OR, 2Bayer CropScience, Research Triangle Park, NC, 3Bayer CropScience, Spangle, WA (19)

ABSTRACT

Indaziflam is a new cellulose biosynthesis inhibitor under development as a preemergence broadspectrum herbicide. This new active ingredient from Bayer CropScience is expected to be available for use in perennial tree fruit, nut, and vine crops as Alion. Pending approval by EPA, Alion will provide residual preemergence control of monocot and dicot weeds with excellent crop safety when applied alone or in a tankmix with other herbicides such as glufosinate (Rely 280).

 In 2010, fifteen trials were conducted by university and Bayer CropScience researchers to compare fall and spring application timings of Alion. These trials were established in eleven states and included six different crops, 41 annual dicot weeds, nine annual monocot weeds, and 19 perennial weeds. Data was split by weed life cycle (annual versus perennial), weed type (dicot versus monocot), and evaluation date (4-6 months after fall application, 7-9 months after fall application, and 10-12 months after fall application).

Evaluations show that 73 g ai ha-1 indaziflam (5 fl oz Alion) plus a burndown product such as glufosinate (Rely 280) applied in the fall provided 90% or higher control of annual monocot and dicot weeds through the spring (4-6 months after application) and summer (7-9 months after application). The same fall applied treatments controlled the perennial weeds 90% 4-6 months after the fall application but declined by the later evaluations.

The same rate of Alion (73 g ai ha-1 indaziflam) applied in the spring also gave excellent residual control of annual weeds however this timing showed the importance of tankmixing an effective burndown product to control weeds already emerged at the time of application. Initial ratings of the spring applications of Alion showed 70-80% control of annual weeds however once the existing weeds were finally burned down excellent residual control (95%) of newly emerging weeds remained for the duration of the trials. Similar to the fall applications, the applications in the spring were less effective on perennial weeds than on annual weeds as Alion has little effect on existing plant tissue which contributes to an excellent safety profile in perennial crops.

In summary, Alion applied in fall is a viable treatment option in addition to the more common spring application timing. Alion provided excellent residual preemergence control of annual monocot and dicots, superior to most standards tested and demonstrated excellent crop safety.




GLOBAL DISTRIBUTION OF GLYPHOSATE RESISTANT WEEDS. I. M. Heap*; WeedSmart, Corvallis, OR (20)

ABSTRACT

Glyphosate has been used since the 1970’s as a broad spectrum herbicide and its usage has steadily increased since then, to become the largest selling crop protection product. The steady increase in area treated with glyphosate globally has been driven by a number of factors. Price reductions in the 1980’s and 1990’s, along with a movement towards zero tillage (requiring more glyphosate for weed control) initiated the increase. This was followed by the introduction of glyphosate-resistant crops, along with the chemical patent expiration, which led to massive price reduction. Since the introduction of glyphosate-resistant crops there has been a steady increase in the number and area of glyphosate-resistant weeds. This is as a direct result of the increase in use of glyphosate in glyphosate-resistant crops. Certainly the first appearances of glyphosate-resistant weeds were not as a result of the introduction of glyphosate-resistant crops. Rigid ryegrass (Lolium rigidum) in Australia, and goosegrass (Eleusine indica) in Malaysia were the first reported field selected cases of glyphosate-resistant weeds, and both were in orchards. Horseweed (Conyza canadensis) was the first case of a glyphosate-resistant weed appearing in a glyphosate-resistant crop (soybean) when it was found in Delaware and Tennessee in the USA. Glyphosate-resistance in horseweed resulted from the repeated use of glyphosate in the absence of an IWM program. At present 21 weeds have evolved resistance to glyphosate globally. Eleven of the 21 glyphosate-resistant weed species have evolved resistance in Roundup Ready cropping systems in the USA, Brazil, and Argentina. The others have primarily evolved resistance in orchards and non-crop situations in Australia, Malaysia, South Africa, Spain, and Chile where glyphosate has been used several times a year over a 20 to 30 year period. The most economically significant in glyphosate-resistant crops are Palmer amaranth and horseweed. Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) has rapidly covered a large portion of the glyphosate-resistant cotton producing regions of the USA. It is now by far the most serious glyphosate-resistant weed. Glyphosate-resistant horseweed is very widespread in the corn/soybean rotations in the USA and is relatively easy to control with other herbicide modes of action, such as the synthetic auxins. Other potentially serious glyphosate-resistant weeds are common waterhemp (Amaranthus tuberculatus), giant and common ragweed (Ambrosia spp), and Johnsongrass (Sorghum halpense).

 




EFFECT OF MANGANESE ON GLYPHOSATE ACTIVITY. N. Soltani*, C. Shropshire, P. H. Sikkema; University of Guelph, Ridgetown, ON (21)

ABSTRACT

Four field trials were conducted from 2007 to 2010 in Ontario to evaluate the effect of various manganese formulations (Ecoman, 5% Mn; MangaMax, 5.5% Mn; ManMax, 5.5% Mn; Superman, 5% Mn; Stoller This, 5% Mn; Nortrace, 6% Mn-EDTA; Nortrace, 22% Mn; and WolfTrax, 33% Mn) applied at 2.0 kg actual Mn/ha on glyphosate efficacy (900 g ae/ha) in glyphosate resistant soybean. There were no manganese deficiency symptoms in soybean at the sites where the experiments were conducted. The tankmix of glyphosate plus Superman, Nortrace (6% Mn-EDTA) or WolfTrax caused as much as 6, 17, and 4% injury in soybean, respectively. There was minimal crop injury (0-1.4%) with other glyphosate plus Mn tankmixes. The addition of Superman or Nortrace (6% Mn-EDTA) to glyphosate did not antagonize glyphosate efficacy on the weeds evaluated (AMBEL, AMARE, CHEAL, and SETVI). The other Mn formulations antagonized glyphosate efficacy for the control of AMBEL, AMARE, CHEAL, or SETVI under some environments. The addition of ManMax or Nortrace (6% Mn-EDTA) to glyphosate reduced soybean yield as much as 15 and 10%, respectively. Based on these results the addition of manganese to glyphosate antagonizes weed control efficacy. The extent of the antagonism is dependent on the specific manganese formulation. Therefore, it is recommended that glyphosate and manganese applications be applied sequentially to avoid weed control antagonism and maximize soybean yield.




HERBICIDE PROGRAMS FOR ENHANCED GLYPHOSATE-RESISTANT AND GLUFOSINATE-RESISTANT COTTON. D. S. Riar*, J. K. Norsworthy, G. M. Griffith; University of Arkansas, Fayetteville, AR (22)

ABSTRACT

Research was conducted at experimental research stations near Keiser and Marianna (Marianna-A), AR, in 2007 and in a grower’s field near Marianna (Marianna-B), AR, in 2008 to compare herbicide programs including POST application(s) of glyphosate/glufosinate alone or in combination with residual herbicides applied as PRE, MPOST, and layby POST-directed (PD) in enhanced glyphosate- and glufosinate-resistant cotton.  Weed species evaluated included Palmer amaranth, pitted morningglory, hemp sesbania, barnyardgrass, and a mixture of large crabgrass and goosegrass.  At Marianna-B, the Palmer amaranth population was a mixture of glyphosate-resistant and -susceptible plants.  For both cotton cultivars and at all locations, inclusion of S-metolachlor plus fluometuron PRE increased weed control and/or decreased the number of glufosinate or glyphosate applications.  At Marianna-B, PRE residual herbicides and/or glufosinate were required to control glyphosate-resistant Palmer amaranth.  Addition of pyrithiobac to glufosinate or glyphosate did not increase weed control.  A layby PD application of flumioxazin plus MSMA was required to increase late-season control of all weed species in glufosinate POST-only programs but not in glyphosate POST-only programs.  None of the programs caused >5% injury to either cotton cultivar.  Seed-cotton yield was similar in all herbicide programs at Keiser and Marianna-A, except for cotton in the POST-only program without a layby PD application, which yielded less than that in PRE fb POST programs in glyphosate-resistant cotton at Keiser.  In general, PRE herbicides did not increase cotton yield but did provide improved early- and late-season control of glyphosate-sensitive and -resistant weeds in both cotton cultivars.



COMPARISONS OF VARIOUS HEXAZINONE FORMULATIONS ON WEED EFFICACY IN ALFALFA. L. K. Hinrichs*; Helena Chemical Company, Memphis, TN (23)

ABSTRACT

Broadleaf weed control was assessed from applications of Velossa® HD Herbicide (0.30 kg/L hexazinone) and compared to products such as Velpar L® (0.26 kg/L hexazinone) and Velpar DF® (75% w/w hexazinone) in alfalfa (Medicago sativa) for broadleaf weed control. Trials were randomized and replicated three times at multiple locations. Applications were made to alfalfa during dormancy, and rates of each product were normalized to approximately 0.57 and 1.11 kilograms of active ingredient per hectare. Induce® (premium nonionic surfactant) was included at 0.25% v/v with each rate of Velossa, Velpar L and Velpar DF. Additionally, Velossa was applied alone in three separate treatments. Weed species evaluated consisted of Common chickweed (Stellaria media), Common dandelion (Taraxacum officinale), Shepherdspurse (Capsella bursa-pastoris), Wild mustard (Sinapsis arvensis), Prickly lettuce (Lactuca serriola) and Western tansymustard (Descurainia incana richardsoni). Observations for efficacy were visually evaluated approximately 7 DAT and continued at different intervals dependant upon location. All locations compared treatments to untreated check plots. Velossa applied with Induce provided broadleaf weed control similar to or in several instances better than that of Velpar L and Velpar DF. Velossa is a non-flammable, non-corrosive liquid that requires no hazard classification for transportation or storage. It is cold stable down to -15°C and when exposed to temperatures lower than -15°C will reconstitute after warming.




WHEAT CONTRIBUTES TO WEED CONTROL AS A ROTATIONAL CROP IN KENTUCKY. J. R. Martin*, C. R. Tutt, D. L. Call; University of Kentucky, Princeton, KY (24)

ABSTRACT

Wheat contributes to weed control as a rotational crop in Kentucky.  James R. Martin, Charles R. Tutt, and Dorothy L. Call, University of Kentucky, Princeton.

 

A common rotation in Kentucky involves three crops over a period of two years.  Corn is planted in the spring of the first year followed by fall-planted wheat. Soybeans are planted the second year in early to mid June after wheat harvest.  This rotation accounts for approximately 27 percent of soybean acres, 33 percent of corn acres, and nearly 75 percent of wheat acres in Kentucky.  Most of the remaining corn and soybean acres are grown in rotation with one another, while the remaining wheat acres are grown as a cover crop after tobacco or used for silage or hay in rotation to corn.

 

Many believe wheat is beneficial to weed control in a rotation with soybeans and corn.  Based on a recent survey of growers, dealers, and consultants; sixty-nine percent of the participants believed wheat improves weed control; while 30 percent indicated it has no impact on weed control; and only one percent indicated less weed control compared with not having wheat in the rotation with soybeans and corn.

 

A recent experiment at University of Kentucky Research and Education Center evaluated the impact of wheat on horseweed (Conyza canadensis) and giant ragweed (Ambrosia trifida).  Horseweed and giant ragweed are annuals that can emerge early and be a problem in soybeans in Kentucky. Each species was evaluated in a separate study.  Wheat was planted at 183 or 333 viable wheat seed m-2 and compared with a winter fallow area to determine the effect of wheat and its seeding rate on emergence or growth of these two weeds. Giant ragweed and horseweed plant counts were determined in four areas of each plot on June 7, 2010.  Data from the wheat plots were taken from the skip row (36 cm wide) on the left and right side of each plot and from a regular row (18 cm wide) from the left and right side of the area to be harvested.  A quadrat of 0.372 m-2 was used to quantify weed density from four random areas within each fallow plot (i.e. 0 seeding rate).  In order to compare data between the different sampling areas, the densities were based on plants per 9.3 m2.

 

Results of the giant ragweed study indicated wheat plots had substantially fewer giant ragweed plants per 9.3 m2 compared with those in the fallow plots.  Wheat plots that were seeded at the normal rate of 333 seeds m-2 tended to have slightly fewer plants than those seeded at 183 seed m-2, regardless whether they were sampled from the skip rows or the normal rows in the harvest area.  There was a strong trend of fewer plants in the narrow rows than in the wide rows.  Giant ragweed plants were considerably shorter in the wheat plots compared with those in the fallow plots.  Plants in the wheat plots ranged from 58 cm to 68 cm while those in the fallow areas averaged 163 cm. Plants tended to be shorter in plots planted at the normal rate of 333 seed m-2 than those in plots planted at 183 seed m-2.

 

Results of the horseweed study also indicated wheat had substantially fewer plants per 9.3 m2 compared with those in the fallow plots.  Wheat plots that were seeded at the normal rate of 333 seed m-2 tended to have slightly fewer plants than those seeded at 183 seed m-2, yet the difference was greater in the skip rows than the harvested rows.  The impact of the row width on horseweed density was similar to that observed with giant ragweed.  There was a strong trend in fewer plants in the narrow rows than those in the skip rows.   Plant heights of horseweed were numerically less in the wheat plots compared with heights in the fallow areas, yet none of the differences were statistically significant.  Appreciation is expressed to the Kentucky Small Grain Growers’ Association for their support of this research.  jamartin@uky.edu




ORGANIC AND HERBICIDE-FREE SYSTEMS APPLIED TO OLD CONSERVATION TILLAGE PLOTS: THE WEED MANAGEMENT CHALLENGE. A. Legere*1, C. Stevenson2, A. Vanasse3, O. Lalonde3; 1Agriculture and Agri-Food Canada, Saskatoon, SK, 2Private Consultant, Saskatoon, SK, 3Université Laval, Québec, QC (25)

ABSTRACT

The success of conservation tillage in organic farming depends on high standards of management, including diversified crop rotations, and an IWM approach. A study was initiated at La Pocatière, Québec, in 2007 to compare the effects a herbicide-free (HF) system and a system based on agronomic practices used in organic agriculture (ORG) to that of cropping systems using either regular (CONV) or GM crops on weed communities and crop yield. The cropping systems were applied to three well established (since 1987) tillage treatments (MP: moldboard plow, CP: chisel plow, NT: no-till) in a four-year barley - red clover - corn - soybean rotation (2007-2010). In the 2009 corn crop, weed density increased as tillage (p<0.001) and synthetic input use (p<0.001) were reduced. Tillage effects on weed biomass varied with cropping system (p=0.008), the tillage effect (NT>CP & MP) being greater in HF than in other cropping system. Corn yields in CONV and GM were 25% greater than those in HF and ORG (p=0.009), regardless of tillage (p=0.396). CP yields were similar for all systems except ORG. The HF system with CP produced corn yields comparable to those in CONV and GM systems whereas the HF and ORG systems with NT failed to produce a corn crop. Mechanical weed control operations (one pass Hiniker cultivator / one pass Hatzdenbichler harrow) failed to control weeds in these systems. In the subsequent soybean crop (2010), tillage effects on weed density varied according to cropping system (p=0.020). Weed density in HF and ORG systems with CP was greater than in other treatments. Weed biomass increased as tillage (p=0.001) and synthetic input use (p=0.013) were reduced. Weed biomass in HF and ORG systems with CP and NT was greater than in other treatments. Tillage had no effect on soybean yield in CONV (p=0.480) and GM (p=0.154) systems. Yields in HF and ORG with MP were similar to those in CONV and GM (p=0.108). The HF and ORG systems with MP produced soybean yields comparable to those in CONV and GM systems. The HF and ORG systems with CP and NT produced a soybean crop but yields were half or less those in other treatments. Mechanical weed control operations (stale seedbed + one pass Hatzdenbichler harrow) failed to control weeds. Including a forage crop prior to corn did not provide expected benefits in ORG-NT, because of poor red clover establishment. Some form of primary tillage (CP, MP) was needed to achieve adequate weed control and yield in both corn and soybean in ORG and HF systems.



GLUFOSINATE EFFECTS ON NITROGEN NUTRITION, GROWTH, AND YIELD OF GLUFOSINATE-RESISTANT AND GLUFOSINATE-SENSITIVE SOYBEAN. K. N. Reddy*1, R. M. Zablotowicz1, N. Bellaloui1, W. Ding2; 1USDA-ARS, Stoneville, MS, 2Northeast Agricultural University, Harbin, Peoples Republic (26)

ABSTRACT

When glufosinate is applied to glufosinate-resistant crops, drift to non-glufosinate-resistant crops may cause injury, disrupt nitrogen metabolism, and reduce yields. A 2-yr field study was conducted during 2009 and 2010 to determine glufosinate effects on plant injury, chlorophyll content, nodulation, nitrogenase activity, leaf and seed nitrogen content, yield, and seed composition in soybean. Glufosinate drift was simulated by application at 45 g/ha to glyphosate-resistant and conventional (glufosinate-sensitive) soybean at 3 weeks after planting (WAP). Glufosinate effects were also evaluated in glufosinate-resistant soybean at 450 g/ha (1x) applied twice at 3 and 6 WAP. In glufosinate-resistant soybean, chlorophyll content, nitrogenase activity, root respiration, plant biomass, soybean yield were not affected while seed nitrogen and protein were increased and seed oil content decreased. In glufosinate-sensitive soybean, glufosinate caused 28-32% injury and decreased chlorophyll content by 42% within 3 d after treatment (DAT) but soybean completely recovered by 14 DAT. Glufosinate had no effect on plant biomass, nitrogenase activity, and root respiration in 2009 but had inconsistent negative effect in 2010. Glufosinate had no effect on yield; increased leaf nitrogen at R4 growth stage, seed protein, and oleic acid; and decreased oil content, linoleic, and linolenic acid in glufosinate-sensitive soybean. In a greenhouse study, glufosinate at 0.3x decreased root and shoot biomass, nitrogenase activity, and root respiration in glufosinate-sensitive soybean, while glufosinate at 3x rate had no affect on these parameters in glufosinate-resistant soybean. These results demonstrate that glufosinate-sensitive soybean exposed to glufosinate drift may exhibit transient injury but soybean could recover over time without a yield penalty. Altered nitrogen accumulation and seed composition in response to glufosinate were observed in all soybean types.



WEED STRESS DURATION EFFECTS ON SOYBEAN GENE EXPRESSION AND YIELD. S. A. Hansen*1, S. A. Clay1, D. P. Horvath2, G. Reicks1; 1South Dakota State University, Brookings, SD, 2USDA-ARS, Fargo, ND (27)

ABSTRACT

Transcriptome analysis is a tool used to investigate gene expression changes induced by specific stresses to an organism. An investigator can use this technology to observe changes taking place in the organism that may not be observed in outward appearance.  Previous studies performed by this laboratory have indicated weed pressure induces the alteration of gene expression in maize as early as the V2 stage, although yield losses may not be significant. A similar study is being conducted in soybean, investigating the differences in gene expression induced by weed pressure removal at the V1 and V3 growth stages.  Microarray or transcriptome analysis technology can be a powerful tool. Unfortunately, it is not an easy technique to master. Our laboratory has successfully performed transcriptome analysis on maize over the past three years. Although preliminary soybean transcriptome data was anticipated for this presentation, difficulties in dye-labeling, hybridization optimization, and slide quality performance were encountered. Multiple protocols were investigated, and a combination of three protocols was the final protocol used for obtaining data.




CAMELINA TOLERANCE TO SOIL-APPLIED HERBICIDES. P. Jha*1, R. Stougaard2, J. O. Garcia1; 1Montana State University, Huntley, MT, 2Montana State University, Kalispell, MT (28)

ABSTRACT

Field experiments were conducted in Northwestern Agricultural Research Center, Kalispell, and in Southern Agricultural Research Center, Huntley, MT, in 2009 and 2010, respectively, to determine the tolerance of Camelina sativa cv. ‘Ligena’ to soil applied preemergence herbicides.  Camelina was seeded 0.6 cm deep at 5.6 kg ha-1 in 17.8-cm wide rows on May 4, 2009 in Kalispell and March 29, 2010 in Huntley.  The soil type at Kalispell was very fine sandy loam, while the soil at the Huntley site was Fort Collins and Thurlow clay loam.  Experiments were conducted in a randomized complete block design with a factorial arrangement of treatments and four replications.  Treatments included herbicides dimethenamid (Outlook), pendimethalin (Prowl), quinclorac (Paramount), metolachlor (Cinch) and pyroxasulfone (KIH-485) applied preemergence at three different rates.  A non-treated control was included for comparison.  Percent crop injury was visually rated at 40 days after application (DAA) using a scale of 0 to 100, where 0 represents no injury and 100 represents complete injury or plant death.  Plant density and biomass were determined by collecting the above ground biomass from two 2-m2 quadrates placed at the center of each plot 90 DAA.  Plant height (90 DAA) and days to flowering were recorded.  Plots were kept weed-free by hand weeding until harvest.  Depending on the herbicide and rate applied, crop injury was 0 to 78% in 2009 at Kalispell (sandy loam soil) compared with 0 to 35% injury in 2010 at Huntley (clay loam soil).  Injury from intermediate to high rates of dimethenamid (0.94 and 1.26 kg ai/ha), pendimethalin (4.26 kg ai/ha), and metolachlor (3.2 kg ai/ha) and low to high rates of pyroxasulfone (0.06 to 0.25 kg ai/ha) exceeded 37% in 2009.  In 2010, injuries greater than 31% were evident only at high rates of pyroxasulfone (0.25 kg ai/ha) and pendimethalin (4.26 kg ai/ha).  Across years and locations, quinclorac (0.28 to 0.84 kg ai/ha) caused the least injury (0 to 10%).  Crop injury due to herbicides mainly occurred as plant density reductions, but stunting also contributed to the injury.  Although several treatments reduced plant densities, late-season measurements including plant height and biomass did not differ.  This suggests that camelina has robust growth and compensatory abilities.  In 2009, only dimethanamid treatment at the high rate yielded lower than the non-treated check (2203 kg/ha).  In 2010, high rates of dimethenamid and pendimethalin and intermediate to high rates of pyroxasulfone caused up to 31% yield reductions compared to the non-treated check (2395 kg/ha).  In conclusion, all herbicides evaluated except quinclorac caused early-season injury to camelina, especially at high rates in sandy soils.  There is a need for further evaluation of these soil applied herbicides for use in camelina under a wide range of soil and environmental conditions.




HERBICIDES FOR WEED MANAGEMENT IN PERENNIAL GRASSES GROWN FOR BIOFUEL. R. Van Acker, J. O'Sullivan*, R. Grohs, R. Riddle; University of Guelph, Simcoe, ON (29)

ABSTRACT

Research was conducted to evaluate herbicides for weed control in four perennial grass crops. The response to PRE and POST herbicides, representing a broad range of herbicide groups, was evaluated. No herbicides are currently labeled in Ontario for use in crops grown for biomass. Weed control during the first growing seasons is essential for successful crop establishment. The challenge is to find herbicides with activity on grass weed species that do not injure the crop or reduce biomass yield. The objective of these studies was to identify suitable candidate herbicides for registration and labeling to manage weeds in switchgrass, big bluestem, prairie cordgrass and miscanthus.  PRE treatments that gave broadleaf weed control, across all crops, with no injury, included saflufenacil, quinclorac and mesosulfuron-methyl. Several herbicides POST gave good control of broadleaf weeds without crop injury. Dichloroprop/2,4D and bromoxynil/MCPA gave 78 and 89% control of broadleaf weeds, across all crops, respectively.  As expected, it was much more difficult to achieve good grass weed control.  Several herbicides with significant activity on grass weed species exhibited injury ranging from 15 to 40%. Quinclorac PRE and Quinclorac POST also gave 100% control of grass weeds, with no crop injury, across all crops. The density of weeds present in the non-weeded control plots compared with treated plots confirmed the need for weed control to ensure successful crop establishment. Herbicides that can be used safely to provide acceptable levels of broadleaf and grass weed control were identified. This will lead to improved weed control options that growers could potentially use when establishing these bioenergy crops.




BAS 810H:APPLICATION TIMING AND RATE FOR IMPROVED CROP SAFETY AND WEED CONTROL IN SPRING WHEAT. A. Anand*1, P. Jha2, J. O. Garcia2; 1Montana State University, Bozeman, MT, 2Montana State University, Huntley, MT (30)

ABSTRACT

An experiment was conducted in 2010 at the Southern Agricultural Research Center, Huntley, MT, to evaluate BAS 810H rate and application timing for improved crop safety and broadleaf weed control in spring wheat.  BAS 810H is a new product from BASF containing dicamba (<50% w/w).  The objective of this research was to determine if the window of dicamba application in spring wheat could be widened beyond the 5- to 6-leaf stage of spring wheat.  Wheat variety “Choteau” was planted on April, 6, 2010.  Major broadleaf weeds present at the test site were kochia, Russian thistle, and prickly lettuce.  The experiment was conducted in a randomized complete block design with four replications.  Crop tolerance and efficacy of BAS 810H was compared with dicamba (Banvel) applied at two stages of wheat1) post-tillering prior to jointing and 2) post-jointing when second joint is at the soil surface.  At the post-tillering timing, BAS 810H and dicamba were applied at 0.32 L/ha and 0.14 kg ai/ha, respectively.  At the post-jointing stage, BAS 810H and dicamba were applied at 0.16 L/ha and 0.07 kg ai/ha, respectively, in addition to the post-tillering rates.  Both herbicides were tank-mixed with 0.59 kg ai/ha of 2,4-D (LV6) and 0.25% v/v non-ionic surfactant (NIS).  Additional treatments comprising of bromoxynil plus MCPA (Bronate Advanced) at 0.28 kg ai/ha with 0.25% v/v NIS at the post-tillering stage and pyrasulfotole plus bromoxynil (Huskie) at 0.22 kg ai/ha with 0.25% v/v NIS and ammonium sulfate (1.12 kg/ha) at the post-jointing stage were included for comparison.  All herbicides were applied using a CO2-powered backpack sprayer equipped with 8001 flat-fan nozzles delivering 93.5 L ha-1.  Crop injury and weed control were evaluated at 1, 3, and 6 wk after application (WAA) by visual rating on a scale of 0 to 100%, with 0% being no control or no injury and 100% being complete control or plant death.  Wheat yields were recorded at harvest.  Wheat injury with dicamba and BAS 810H did not differ and averaged 12 and 7% at post-tillering and post-jointing timing, respectively.  Bromoxynil plus MCPA caused less injury (1%) compared with dicamba or BAS 810H, when applied at the post-tillering stage.  Injury with pyrasulfotole plus bromoxynil was 1% and did not differ from other post-jointing treatments.  Kochia, Russian thistle, and prickly lettuce control 6 WAA with BAS 810H applied at the post-tillering stage was 89, 90, and 90%, respectively, and was higher than 80, 81, and 83% control, respectively, with bromoxynil plus MCPA.  Reducing BAS 810H rate from 0.32 to 0.16 L/ha at the post-jointing timing reduced kochia and prickly lettuce control.  Delaying BAS 810H or dicamba application to the post-jointing stage did not influence weed control.  Kochia, Russian thistle, and prickly lettuce control 6 WAA with BAS 810H (0.32 L/ha) was 86, 89, and 86%, respectively, and did not differ from the pyrasulfotole plus bromoxynil applied post-jointing.  Except a slight reduction in yield with dicamba compared to bromoxynil plus MCPA at the post-tillering timing, wheat yields did not differ across herbicide treatments and ranged from 5578 to 6250 kg ha-1.  In conclusion, BAS 810H applied at 0.32 L/ha beyond the 6-leaf stage of spring wheat provided optimum crop safety and weed control.

 

 

 




MODELING “HABITAT SUITABILITY” FOR A HERBICIDE RESISTANT WEED USING A SPECIES DISTRIBUTION MODEL AND PRESENCE-ONLY DATA. L. Wiles*1, S. Kumar2, V. M. Davis3, B. Johnson4; 1USDA-ARS, Fort Collins, CO, 2Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 3University of Illinois, Urbana, IL, 4Purdue University, West Lafayette, IN (31)

ABSTRACT

Herbicide resistant weeds are like invasive weeds: prompt management is needed to prevent their spread. For invasive weeds, first reports of a weed's occurrence are often analyzed with species distribution models (SDM) to prioritize detection and treatment. Suitability of other areas as habitat for the weed is estimated using the observed locations, environmental data, and an appropriate SDM for the available data. Compared to invasive weeds, the presence of herbicide resistance weeds is driven more by crop management than environment, yet SDMs might be similarly used. After a resistant weed has been found in a few fields, the risk of resistance in other fields might be estimated from information about the environment and past crop management. We tested this idea with three SDMs and data on presence of glyphosate-resistant (GR) horseweed (Conyza canadensis) in Indiana corn fields. Prediction of the presence of GR plants from presence-only data using MAXENT was compared with prediction from presence/absence data using either CART or Boosted Regression Trees. The latter two models require data from fields where no GR weeds are present but MAXENT does not. All three models fit the data well and identified ‘visible injury’ and ‘weed abundance’ as the most important predictors of GR. MAXENT was the best at prediction, supporting the use of SDMs and first reports of resistance to advise farmers about which fields are most at risk. Environmental data for this use of SDM are readily available; the challenge will be collecting historical crop management information.



RESISTANCE TO HERBICIDES IN PHALARIS SPP. AND AVENA FATUA IN THE BAJíO REGION OF MEXICO. T. Medina-Cazares*1, R. Alarcón-Reverte2, J. C. Streibig3, A. J. Fischer2; 1INIFAP, Celaya, Mexico, 2University of California, Davis, Davis, CA, 3Royal Veterinary and Agricultural University, Thovarldsenvej, Denmark (32)

ABSTRACT

Wheat and barley are the most important crops in autumn-winter season of the Bajio in the State of Guanajuato, Mexico. Two of the most troublesome weeds in these crops are wild oat (Avena fatua) and littleseed canarygrass (Phalaris spp.). In recent years an increasing number of control failures have led to investigate herbicide resistance in these weeds. In this study, dose-response experiments were carried out to determine cross-resistance patterns among herbicides with two modes of action, acetyl-CoA carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors. The herbicides evaluated were the ‘fops’ clodinafop-propargyl and fenoxaprop-P-ethyl, the ‘dim’ tralkoxydim, and the two ALS inhibitors flucarbazone-Na and mesosulfuron-iodosulfuron-methyl. Results indicated that cross-resistance to the ACCase-inhibiting herbicides fenoxaprop-P-ethyl, clodinafop-propargyl and, to a slightly lesser extent, tralkoxydim, was widespread. In contrast, resistance to the ALS-inhibiting herbicides was less common but still present. The three ACCase-inhibitors studied here have been used in the area of Guanajuato for many years since their introduction in Mexico, while the two ALS-inhibitors had not yet been introduced in Mexico by the time seed samples were collected. Thus, resistance to these ACCase inhibitors can be associated with their continuous use for many years in this area. These ALS-inhibitors, however, had been applied only a few times in trial fields in the area by the time seed samples were collected, which suggests either the rapid evolution of resistance to ALS-inhibitors in these plants, cross-resistance prior to their introduction as a consequence of selection pressure imposed by herbicides with different modes of action.



CAN INTER-ROW SOIL DISTURBANCE AT SEEDING LEAD TO EFFICIENT LOCALIZED WEED CONTROL USING PLANT COVER DETECTION? M. Simard*1, B. Panneton2, G. D. Leroux3, A. Vanasse4, R. E. Nurse5; 1Agriculture and Agri-Food Canada, Quebec, QC, 2Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC, 3Université Laval, Quebec, QC, 4Université Laval, Québec, QC, 5Agriculture and Agri-Food Canada, Harrow, ON (33)

ABSTRACT

Site-specific spot spraying coupled with real time weed detection could reduce herbicide input in field crops without increasing fuel and time expenses (e.g. mechanical weeding) or yield reduction risks (e.g. reduced herbicide rates). However, real time weed detection is constrained by weed/crop discrimination. This hurdle could be bypassed if weeds were detected in the inter-row only. However, weed cover could be lower on the inter-row than on the row due to increased weed germination from soil disturbance by the seeding equipment at seeding. Therefore, disturbing the inter-row at seeding could even out weed cover. Our goal was to disturb the soil in inter-rows at seeding (using press wheels and hoes) and evaluate differences in weed density, cover and biomass between rows and inter-rows. The experimental design included two separate (corn or soybean) RCB experiments, four fields and four blocs. Six soil disturbance treatments were tested: 1) light press wheel (LW), 2) heavy press wheel (HW), 3) tooth (T), 4) light press wheel + tooth (LWT), 5) heavy press wheel + tooth (HWT), 6) Control (no treatment). One day before herbicide application, weed cover (using digital images), density and biomass were evaluated in paired narrow rectangular plots (short side centered in the disturbed inter-row or the adjacent row section). There were no differences in weed density generated by the treatments (p>0.05). In corn, adjacent rows and disturbed inter-row sections had similar weed cover and biomass. In soybean, weed biomass or cover was generally higher on the inter-rows. Results from the first year (a second trial will be done in 2011) suggest inter-row plant cover detection would not underestimate weed pressure, even if the inter-row is left undisturbed.



EFFECT OF HERBICIDE RATE AND ROTATION ON THE WEED SEED BANK AFTER THREE YEARS OF TRANSGENIC CORN/SOYBEAN CROPPING. M. Simard*1, S. Rouane2, G. D. Leroux2; 1Agriculture and Agri-Food Canada, Quebec, QC, 2Université Laval, Quebec, QC (34)

ABSTRACT

Exclusively transgenic-based herbicide/crop rotations are now possible in corn/soybean cropping systems. In ploughed fields, efficient weed control can be obtained in these rotations with a single post-emergence application of a broad-spectrum herbicide that has low environmental toxicity. Reducing herbicide rates in this type of system might lower its environmental impact even further. The seed bank resulting from three years (2006 to 2008) of different herbicide rates in a cropping system where glyphosate/glufosinate and corn/soybean were rotated, or not, was therefore evaluated in a field located in St-Augustin-de-Desmaures, Québec, Canada. Ploughed field plots were seeded in corn every year, or corn and soybean (one year). These plots received the same herbicide every year or various glyphosate/glufosinate 3-yr rotations. Subplots were sprayed with a single post emergence application of the recommended rate of glyphosate (900 g ae ha-1) or glufosinate (500 g ai ha-1) or lower rates. Subplots received the same full (1X, recommended) or reduced (0.5X, 0.75X) rate every year. Soil cores were extracted in 2008 to evaluate the resulting seed bank. Seed bank decline with increasing rates was described using an exponential decay function. Data for annual broadleaves was well fitted to this equation, suggesting a steep decline in seed banks up to ca. 400g ha-1. The seed bank of annual grasses was more variable. Including glufosinate in the rotation increased seed banks due to the lower efficacy of the glufosinate rates tested at reducing the seed bank of annual grasses. Including soybean in the cropping system resulted in lower seed banks compared to continuous corn cropping



WEED CONTROL WITH PINDAR GT IN CALIFORNIA TREE NUTS. R. K. Mann*1, M. Sorribas1, J. P. Mueller2, B. Bisabri3, M. L. Fisher4, D. G. Shatley5, J. Richardson6; 1Dow AgroSciences, Indianapolis, IN, 2Dow AgroSciences, Brentwood, CA, 3Dow AgroSciences, Orinda, CA, 4Dow AgroSciences, Fresno, CA, 5Dow AgroSciences, Lincoln, CA, 6Dow AgroSciences, Hesperia, CA (35)

ABSTRACT

PindarTM GT (penoxsulam + oxyfluorfen) is a new broadspectrum tree nut herbicide product being launched in the United States for the control of many winter annual weeds in almonds, walnuts, pistachios and pecans.  Pindar GT is a 4.04 lb ai/gallon SC (Suspension Concentrate) formulation premix containing 10 g of penoxsulam + 476 g of oxyfluorfen/liter.  Pindar GT provides pre-emergence and post-emergence control of glyphosate resistant and susceptible marestail (Conyza canadensis) and fleabane (Conyza bonariensis), as well as the control of many other winter annual weeds including annual bluegrass (Poa annua), annual sowthistle (Sonchus oleraceus), California brome (Bromus carinatus), coast fiddleneck (Amsinckia intermedia), common chickweed (Stellaria media), cudweed (Gamochaeta spp.), cutleaf eveningprimose (Oenothera laciniata), filaree (Erodium spp.), henbit (Lamium amplexicaule), mallow (Malva spp.), mustards (Sinapis and Brassica spp.), prickly lettuce (Lactuca serriola), redmaids rockpurslane (Calandrinia ciliata), rosemallow (Hibiscis spp.), shepherd’s purse (Capsella bursa-pastoris), and willowherb (Epilobium spp.).

Pindar GT at 1.5 to 3.0 pints/acre will provide from 3 to 6 months residual weed control of many winter annual weeds when applied during the winter dormant period from October to February, providing equivalent or better weed control than other standards. For complete burndown of all existing weeds, tankmix Pindar GT with a broadspectrum postemergence herbicide.

  TM Trademark of Dow AgroSciences LLC




LIBERTYLINK SOYBEAN: IS THIS THE ANSWER? D. Lingenfelter*, W. Curran; The Pennsylvania State University, University Park, PA (36)

ABSTRACT

As more weeds become resistant to glyphosate, many wonder if the LibertyLink® soybean system will be the answer to this problem. Glufosinate (Ignite 280®, formerly known as Liberty) has the potential for both burndown in no-till and for control of emerged weeds POST. However, there are several benefits and challenges to consider and these are forefront on many university extension weed scientist’s minds. Initial investigations of LibertyLink soybean programs in central Pennsylvania were conducted from 1995 – 1999 and then were revived in 2008 prior to commercial marketing of LibertyLink soybean varieties. Late season evaluations of eight studies revealed that glufosinate herbicide alone provided 80 – 83% control of giant foxtail (Setaria faberi), common lambsquarters (Chenopodium album), velvetleaf (Abutilon theophrasti), and smooth pigweed (Amaranthus hybridus) when applied EPOST.  However, when glufosinate was applied in combination with a PRE-residual herbicide or in a glufosinate (EPOST) followed by glufosinate (POST) program, control of these same weed species improved to 90 – 97%. In burndown studies, initial control from glufosinate alone provided 93 and 86% control of  horseweed (Conyza canadensis) and dandelion (Taraxacum officinale), respectively; however when 2,4-D was included, horseweed and dandelion control increased to 99 and 93%, respectively. Benefits of the LibertyLink system include: good, in-crop, annual weed control option; use of a different mode of action (non-glyphosate) as a possible herbicide resistance management tactic; wide POST application window; currently, no resistant weed species; and good crop rotation flexibility.  Some challenges include: weaker than glyphosate on certain annual weeds and perennials and in burndown situations; thorough spray coverage necessary for effective weed control; time of day and climatic conditions can affect glufosinate performance; and possible higher cost of glufosinate- vs. glyphosate-containing herbicide products. In a well planned crop rotation, LibertyLink soybean system has the potential to provide effective weed control and reduce the reliance on glyphosate when used in an integrated weed management scheme. For example, in no-till LibertyLink soybeans, use a glyphosate-based burndown mixture that includes a reduced rate residual herbicide followed by an in-crop application of glufosinate.




PROGRESS IN CANADIAN MINOR USE WEED SCIENCE PROGRAM. K. Subedi*; Agriculture and Agri-Food Canada, Ottawa, ON (37)

ABSTRACT

Progress in Canadian Minor Use Weed Science Program

 Kalidas Subedi

Agriculture and Agri-Food Canada

Pest Management Centre

Minor Use Program

960-Carling Avenue, Ottawa, ON

K1A 0C6, Canada

 

 

Abstract

 

The Pest Management Centre (PMC) was established in 2003 by the Agriculture and Agri-Food Canada (AAFC) to provide access to newer, safer, and reliable pest control products, and production practices that reduce reliance on pesticides to Canadian growers. Improving access to safe, new and effective products and technologies helps growers increase their competitiveness both domestically and internationally. 

The PMC operates two programs; the Minor Use Pesticide Program and the Pesticide Risk Reduction Program. The Minor Use Pesticide Program works in collaboration with Canadian growers, provinces, chemical companies, Health Canada's Pest Management Regulatory Agency (PMRA), and US-IR-4 Project. PMC addresses the priority pests (i.e. insects, diseases, and weeds) on minor use crops (i.e. low acreage, high value crops) that are identified by growers at an annual Priority-Setting Workshop. PMC generates required data through field and greenhouse trials, conducts laboratory analyses to collect required efficacy and residue data before drafting regulatory submissions to PMRA on behalf of growers for new uses in Canada. Since 2003, the Minor Use Pesticide Program has worked on 206 weed science projects, made 95 submissions on 34 different herbicides and so far, over 60 registrations have been made for 38 crops. Similarly, several pesticides risk reduction approaches have been developed through the Pesticide Risk Reduction Program of PMC.

In addition, the PMC works closely with the IR-4 Project on joint projects where work sharing is resulting in new uses becoming available in both countries simultaneously. This is in addition to PMC’s efforts to work internationally on harmonization of pesticide regulatory requirements to reduce duplication and speeding submission processes. Details of crops, herbicides, and plant growth regulators recently registered for minor use in Canada are summarized. Many of these new uses replace older chemistries and formulations and provide new mode of actions for herbicide resistance management. These efforts assist in moving new products through the regulatory system thereby helping Canadian high value commodities compete in global markets.

 




EFFICACY OF POST-DIRECTED HERBICIDE APPLICATIONS FOR WEED CONTROL IN PEPPER. L. Brandenberger*, L. Carrier; Oklahoma State University, Stillwater, OK (38)

ABSTRACT

Phytotoxicity of post-directed herbicide applications for weed control in pepper.

Lynn Brandenberger*, Lynda Carrier, Oklahoma State University, Stillwater.

 

Postemergence studies were completed with six different herbicides (flumioxazine, carfentrazone-ethyl, glyphosate, saflufenacil, pyrithiobac-sodium, pendimethalin) alone and in combination for a total of eight treatments plus a nontreated check.  Although the two studies used the same herbicide treatments they did vary in application dates and application method.  Both studies were transplanted to the pepper cultivar ‘Okala’ on 4/20/10 for the June study and 4/14/10 for the July study.  June treatments were applied on 6/01/10 with a hooded sprayer at a rate of 159 liters per hectare to plots 7.3 x 15.2m and July treatments were applied on 7/22/10 with a shielded sprayer at a rate of 187 liters per hectare to plots 3.6 x 12.1m, both used a randomized design with three replications.  The studies were rated for injury on 6/08/10 and 8/05/10, respectively, for the June and July study sites.  Fresh weight of three random plants per plot was recorded on 10/15/10 at each site.  No differences were observed for injury (0 to 12%) or fresh weights (4.04 to 5.49kg) between treatments or the nontreated check in the June or July studies.  The authors would conclude that postemergence treatments that include flumioxazine, carfentrazone-ethyl, glyphosate, saflufenacil, pyrithiobac-sodium, and pendimethalin when applied with either a hooded or shielded sprayer are not injurious to commercial pepper crops.  Corresponding author: lynn.brandenberger@okstate.edu.

 




THE EFFECT OF VINE KILL HERBICIDES ON POTATO STORAGE AND CHIP QUALITY. W. J. Everman*, C. M. Long, A. J. Chomas; Michigan State University, East Lansing, MI (39)

ABSTRACT

A study was conducted in 2008 and 2009 to investigate the effects of vine kill herbicides on storage quality. Vine kill herbicides act rapidly to desiccate foliage from potato plants prior to harvest. Four herbicides representing 3 classes of herbicides are currently labeled for use as vine kill in potato. We routinely investigate the effectiveness of potato vine kill products in the field; however the effects of vine kill products on tuber quality and storage have not been extensively investigated. There are many physiological effects of herbicides on plant growth and development, and investigating the effects of vine kill herbicides will help determine if storage life and tuber quality are compromised. We evaluated the effect of several available vine kill herbicides and one experimental compound under evaluation on tuber quality at harvest including grade and internal defects, and are determining the effect of vine kill herbicides on potato storage life and chipping quality. Herbicide products were applied on Snowden to test effectiveness of vine kill with herbicide treatments consisting of 1) glufosinate at 28.7 oz/A 2) glufosinate + AMS at 3 lb/A 3) diquat at 1 pt/A followed by diquat at 1 pt 4) BAS 800 at 0.5 oz/A 5) BAS 800 at 1 oz/A 6) BAS 800 at 2 oz/A 7) BAS 800 at 4 oz/A 8) carfentrazone at 3.2 oz/A 9) carfentrazone at 3.2 oz/A fb carfentrazone at 3.2 oz/A. All herbicide treatments were compared with a non-treated control treatment. Vine kill was evaluated weekly after treatment until harvest. Plots were harvested after vine kill and marketable yield was determined. No yield effects were observed due to treatment, and all products resulted in excellent vine kill at the time of harvest. Tubers were then placed by treatment into storage in the new potato storage unit. Tuber samples were taken on a monthly basis to determine sugar levels, internal defects, and chip quality. Few differences were observed between herbicide treatments, with most differences observed due to storage conditions. Results of this research will determine if storage quality and life is affected by herbicide treatments for vine kill. 




POST-DIRECTED APPLICATION OF PELARGONIC ACID FOR SQUASH. C. L. Webber*1, J. W. Shrefler2, L. Brandenberger3; 1USDA-ARS, Lane, OK, 2Oklahoma State University, Lane, OK, 3Oklahoma State University, Stillwater, OK (40)

ABSTRACT

Organic squash (Cucurbita pepo L.) producers need appropriate herbicides that can effectively provide post-emergent weed control.  Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of a potential organic herbicide on weed control efficacy, crop injury, and yields.  The experiment included Scythe® (57% pelargonic acid) applied post-directed at 3, 6, and 9% v/v application rates, plus an untreated weedy-check and an untreated weed-free check with 4 replications.  Yellow squash, cv. ‘Enterprise’, was direct-seeded on June 21, 2010 into raised 91-cm centered beds.  The primary weeds included smooth crabgrass (Digitaria ischaemum  (Schreb.) Schreb. ex Muhl.), cutleaf groundcherry  (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus  L.).  Scythe® was post-directed applied on July 13 and then reapplied  8 days later (July 21).  Grass weed control (78%) and broadleaf weed control (69%) with the 9% Scythe® treatment were at their lowest level at 7 days after the initial spray treatment (DAT).   Smooth crabgrass (98%), cutleaf groundcherry (94%), and spiny amaranth control (94%) control peaked at 9 DAT (1 day after the sequential treatment) with the 9% application rate.  Scythe® at 9% also resulted in the greatest crop injury at 9 DAT (12.5%).  The sequential application of Scythe® significantly increased grass or broadleaf control at all application rates.  The 6 and 9% Scythe® treatments produced equivalent squash yields (squash/ha and kg/ha) as the weed-free treatment and greater yields than the weedy check. 




QUANTIFYING THE COSTS AND BENEFITS OF COVER CROP USE FOR WEED MANAGEMENT. A. H. Cho, A. W. Hodges, C. A. Chase*; University of Florida, Gainesville, FL (41)

ABSTRACT

Cover crops can be used as more sustainable alternatives to clean fallows with herbicides or with multiple tillage operations.  However, they are often overlooked for weed management due to the perceived costs associated with implementing, managing, and terminating cover crops.  Inclusion of a cover crop into a cropping system can provide benefits in addition to weed suppression, such as soil stability, water conservation, nutrient cycling, and reduction in pest and disease pressures.  Although the weed suppression potential of certain cover crops has been demonstrated, economic analyses of these cover crops is lacking.  The objective of this study was to determine the costs and benefits related to utilizing summer fallow treatments prior to an organic summer squash crop in Florida.  Data from several sources were utilized to create partial budgets for five summer fallow treatments; sunn hemp (Crotalaria juncea L.), velvetbean (Mucuna deeringiana (Bort) Merr.), cowpea (Vigna unguiculata (L.) Walp. cv. Iron Clay), sorghum sudangrass (S. bicolor x S. bicolor var. sudanese (Piper) Stapf.), and tillage to manage weeds.  These treatments were compared for the potential for weed suppression and contribution of nitrogen to the squash crop by using biomass and nitrogen calculations.  Partial budgets were used that took into consideration the additional cost of the summer fallow treatments including the cost of seed, inoculants, implementation, management, and termination of the various cover crops, as well as analyzed the benefits that can be realized in the subsequent squash crop through the reduction in the need for fertilizer and weed management.  When only considering the costs of the summer fallow treatments, tillage was the least expensive followed by sorghum sudangrass, cowpea, sunn hemp, and velvetbean.  However, when both the costs and benefits of cover crops are included in the partial budget for squash production, it was concluded that production of squash would be least expensive with the sunn hemp cover crop, followed by velvetbean, cowpea, sorghum sudangrass, and tillage. 

 

Corresponding author’s e-mail address: alycho@ufl.edu



EFFECT OF CONTROLLED RELEASE NITROGEN FERTILIZER ON VINE DESICCATION AND POTATO TUBER YIELD. L. E. Bast*, W. J. Everman, A. J. Chomas, D. D. Warncke; Michigan State University, East Lansing, MI (42)

ABSTRACT

Nitrogen fertilizer is one of the most costly inputs in potato production and the most important input for maximizing potato tuber yield.  Field research was conducted in 2010 to examine the effect of:  1) controlled release fertilizer on vine vigor and vine desiccation, and 2) controlled release and conventional urea-ammonium nitrate on potato yield.  The site was established at the Montcalm Research Farm near Entrican, MI.  The experiment was conducted in a factorial design with four replications.  Individual plots were 3.5 meter wide and 7.6 meter long, consisting of four potato rows spaced at 0.86 meter.  ‘Snowden’ variety tubers were planted on May 17, 2010. Treatments consisted of either controlled release (CR) or conventional 28% urea-ammonium nitrate (UAN) solution applied at a rate of 67 kg/ ha at planting, first cultivation and hilling followed by 112 kg/ha (urea) surface applied in late July for a total of 12 treatments.  Vine kill treatments consisted of diquat + NIS (0.28 kg ai/ha  + 0.25% v/v/ha) followed by diquat + NIS (0.28 kg ai/ha  + 0.25% v/v/ha), gluphosinate (0.43 kg ai/ha), and a control treatment (no vine desiccation).  Irrigation and other potato crop management practices followed that of commercial producers.  Vine desiccation was evaluated visually 14, 21 and 28 days after treatment.   Also, normalized difference vegetation index (NDVI) measurements were collected.  Potato tubers were harvested and yields determined.  There were no significant differences among herbicides in regards to potato vine desiccation.  There was a significant correlation between visual rating and NDVI measurements.  In marketable tuber yield there were no significant differences in yield.




INDAZIFLAM FOR CONTROL OF KEY WEEDS IN TREE, NUT, AND VINE CROPS. D. Unland*1, H. Mager2, M. Edenfield3; 1Bayer CropScience, Research Triangle Park, NC, 2Bayer CropScience, Fountain Hills, AZ, 3Bayer CropScience, Lake Wales, FL (43)

ABSTRACT

Alion is a preemergence herbicide with the new active ingredient, indaziflam, Bayer CropScience has developed for use in perennial tree nut, fruit, and vine crops.  Registration is currently under review and pending approval by EPA.  Field trials were conducted by Bayer CropScience and university researchers across the United States in 2009 and 2010 in major fruit and tree nut production areas.  In these trials 73 g ai ha-1 indaziflam (5 fl oz Alion per acre) provided effective residual control of the most common monocot and dicot weeds.  Weed control for most species tested was similar or superior to other currently registered broad-spectrum herbicides used in these crops.  Excellent crop tolerance was observed in all of these trials.



INDAZIFLAM: A NEW PRE-EMERGENCE HERBICIDE FOR CITRUS. M. -. Singh*1, A. M. Ramirez1, M. Edenfield2; 1University of Florida, Lake Alfred, FL, 2Bayer CropScience, Lake Wales, FL (44)

ABSTRACT

Indaziflam 200 SC is a new herbicide developed by Bayer Crop Science which provides excellent broad-spectrum residual control. A field experiment was conducted in 2009 at the Citrus Research and Education Center, Lake Alfred, FL to compare the efficacy and phytotoxicity of different indaziflam rates in combination with glyphosate. The area was planted to Valencia sweet oranges (Citrus sinensis Pers.).  Treatments for the field study were an untreated check, glyphosate alone at 2.3 li/ha, three indaziflam rates (49, 70 and 91 gm/ha) tank mixed with glyphosate at 2.3 li/ha and norflurazon + diuron (grower’s practice). Treatments were applied twice. For the second application, the indaziflam rates were adjusted so that total rate did not exceed 140 gm/ha per year. The treatments were applied with a tractor mounted boom sprayer fitted with 8002 off center flat spray nozzle set to deliver 187 li/ha at 40 psi. Weed control ratings were done biweekly using the 0-100 rating scale with 0 being no control and 100 being complete control or death of plants. The various rates of indaziflam tank mixed with glyphosate provided greater season-long control of grasses and broadleaf weeds than the farmer’s standard practice (norflurazon and diuron) and glyphosate alone. Guinea grass (Panicum maximum Jacq.) control was 91 to 100% with indaziflam + glyphosate treatments until 277 DAT. Indaziflam + glyphosate also provided 88-100% control of Florida pusley/Brazil pusley (Richardia sp), and > 90% control spanishneedles (Bidens bipinnata L.) and common purslane (Portulaca oleracea L.). All indaziflam treatments did not injure the Valencia trees. These results indicate that Indaziflam 200 SC can be an excellent alternative to the current grower’s practice to better manage weeds in citrus groves. msingh@ufl.edu.




SUMMER WEED CONTROL WITH GLYPHOSATE TANK MIXED WITH INDAZAFLAM OR PENOXSULAM IN CALIFORNIA ORCHARDS AND VINEYARDS. B. D. Hanson, A. J. Jhala*; University of California, Davis, Davis, CA (45)

ABSTRACT

Summer weed control with glyphosate tank mixed with indaziflam or penoxsulam in California orchards and vineyards. Amit J. Jhala and Brad D. Hanson*, Department of Plant Sciences, University of California, Davis, CA, 95616. Tel: 530-752-8115; E mail: bhanson@ucdavis.edu

Abstract

Herbicides are an important component of weed control in perennial, high value crops including walnut and grape in California. If not controlled, weeds may aggravate pest problems and compete with trees for nutrients and water. Indaziflam (submitted for registration) and penoxsulam are new herbicides for weed control in perennial fruit, nut and vine crops. Field experiments were conducted to evaluate residual weed control with indaziflam or penoxsulam compared with flumioxazin and rimsulfuron in established walnut and grapes in Yolo County, CA. At both the sites, treatments included glyphosate alone (2 lb ae/acre) and glyphosate tank mixed with penoxsulam (0.015 or 0.03 lb/acre), indaziflam (0.065 or 0.085 lb/acre), flumioxazin (0.255 or 0.383 lb/acre) or rimsulfuron (0.063 lb/acre). An untreated control was included for comparison. Visual ratings of weeds were taken several times during the season. Data on weed biomass were collected on 6 Aug. and 16 July, 2010 in the walnut and grape trials, respectively.

All treatments resulted in ≥ 85% control of filaree (Erodium spp.), California burclover (Medicago polymorpha), sowthistle (Sonchus spp.), and field bindweed (Convolvulus arvensis) 2.5 weeks after treatment (WAT) in the walnut trial. At this site, little mallow (Malva parviflora) control was less effective with glyphosate applied alone compared to all other treatments at 2.5 WAT, however no difference was observed among treatments at 7.5 WAT. Control of bermudagrass (Cynodon dactylon) was only 26% and 45%, respectively in glyphosate applied alone or tank mixed with flumioxazin compared to other treatments at 15.5 WAT. Total weed biomass was significantly reduced in all treatments compared to untreated plots with some difference among treatments. For example, higher weed biomass was recorded in glyphosate applied alone or in a tank mix with indaziflam at 0.065 lb/acre or flumioxazin compared to other tank mix treatments.  

In the vineyard trial, there was few weed control differences among residual herbicides tank mixed with glyphosate although by early summer, most were slightly better than glyphosate applied alone. For example, panicle willowherb (Epilobium ciliatum) control 2 WAT was poor in all treatments (< 32%), except glyphosate tank mixed with flumioxazin; however, later in the season (20 WAT) willowherb control was better with a tank mix of glyphosate plus penoxsulam at 0.03 lb/acre, flumioxazin or rimsulfuron compared to other treatments. All the treatments reduced weed biomass compared to untreated plots (150 g m-2) in the vineyard trial with no differences among tank mix partners. Herbicides were applied about two months later than the recommended time; therefore it is likely that earlier applications would have improved weed control. Panicle willowherb is not well controlled with glyphosate and additional research is needed on pre- and post-emergence options for this weed in California orchards and vineyards.

 




NEW HERBICIDES FOR WEED CONTROL IN POTATO. C. J. Swanton, K. Chandler*; University of Guelph, Guelph, ON (46)

ABSTRACT

Potato growers in Canada rely on a very limited number of herbicides for broadleaf weed control. Metribuzin and linuron are two of the most important herbicides used by growers to control these weeds. Throughout Canada, weed resistance has been reported in several potato growing areas to both herbicides. Field research has been conducted in Ontario to obtain new herbicide registrations with the assistance of the Agriculture and Agri-Food Canada minor use program. This research has identified several new herbicides that will be of benefit to growers once registration has been achieved.




NATURAL PRODUCT HERBICIDES FOR FRUIT AND VEGETABLE CROPS. R. Van Acker, J. O'Sullivan*, R. Grohs, R. Riddle; University of Guelph, Simcoe, ON (47)

ABSTRACT

Control of weeds remains the most significant agronomic problem associated with the production of organic fruits and vegetables. Studies were conducted to evaluate several biological or low- risk herbicides for crop safety and efficacy in controlling weeds common in the organic production of peaches, tomato, sweet corn and pepper.  The objective of these studies was to provide enhanced weed management in organic fruit and vegetable production. In vegetable crops, Green Match EX plus one cultivation gave the best overall weed control with a final rating of 91%. Green Match EX alone gave a final rating of 71%, while Matratec AG (49%) and Weed Zap (44%) were intermediate, depending on the weed species involved. While level of control varied with weed species, all postemergence treatments gave early-season control that was superior to the standard treatment of 30% acetic acid. Manuka Oil gave the poorest control, ranging from 0 to 54%, averaged over five weekly ratings from June 25 to July 26. Green Match EX with one cultivation gave the highest yields across all crops. Yields from this treatment were equivalent to yields from the weeded control. Green Match EX alone gave excellent tomato and sweet corn yields. Matratec AG and Weed Zap yields were lower while yields with 30% acetic acid were low despite providing adequate weed control. This was likely due to poor early control. Manuka Oil gave significantly reduced yields. There was no effect from any treatment on peach tree diameter, tree height or injury. Weedphyter (RTU) gave the best weed control with a final total weed control rating of 90%. Control, averaged over five weekly ratings from June 25 to July 26, ranged from 46 to 92%. Matratec AG gave excellent control of 88% (range 41-88%) while Green Match EX (15%) gave control of 78% (range 55-91%). Weed Zap gave weed control of 75% (range 24-75%) while Green Match EX (10%) gave control of 56% (range 35-76%).  This research on novel uses of bioactive natural products will lead to improved weed control options that organic growers could potentially use and provide these growers and the public with environmentally and economically sustainable alternatives to synthetic chemical herbicides. This helps in fulfilling society’s desire for reduced dependence on chemical inputs which will reduce risk to human and environmental health.



TOLERANCE OF SEED RADISH TO CLOPYRALID: EFFECT OF VARIETY, TIMING AND RATE. E. Peachey*, A. Greco; Oregon State University, Corvallis, OR (48)

ABSTRACT

Greenhouse and field experiments in 2010 measured the effect of clopyralid on radish grown for seed. In the greenhouse study, 13 male, female, or open pollinated radish varieties were planted in pots, and clopyralid was applied at 0.14 and 0.28 kg ai/ha to radish with 2 to 3 leaves or when radish was about to bolt. Clopyralid caused slight visual symptoms on 3 varieties, but visual injury did not correlate well with effects on shoot and root yield. Clopyralid rate was the primary factor influencing shoot yield; application timing was the main factor influencing root yield. Clopyralid at 0.28 kg ai/ha reduced growth of 2 varieties by 12 and 17% but enhanced growth of another by 41%. The remaining 10 varieties were unaffected by clopyralid. In the field study, clopyralid was applied at 0.14 and 0.28 kg ai/ha to radish at the 4 to 6 leaf stage or just as radish began to flower. Clopyralid caused very little visual injury to radish except when applied at 0.28 kg ai/ha to radish male lines that had just begun to flower. This treatment caused minor injury to the female rows but dry matter and seed yield at harvest were 21 and 31 % less, respectively, than the untreated check. Three different seed germination tests indicated a potential increase in germinability of seeds when clopyralid was applied at 0.28 kg ai/ha to radish that had just begun to flower.




WEED SUPPRESSION UTILIZING MULCH AND ORGANIC HERBICIDE COMBINATIONS. M. A. Rowley*1, C. V. Ransom2, J. Reeve2, B. L. Black2; 1Utah State University, Eureka, UT, 2Utah State University, Logan, UT (49)

ABSTRACT

Abstract- Weed suppression using mulch and organic herbicide combinations

Multiple trials were established to evaluate combinations of mulches and organic herbicides for weed control.  Sites were located at the Greenville Research Station, Logan, UT and Kaysville Research Station, Kaysville, UT.  Plots were prepared in mid-summer of 2009 by disking the ground multiple times and then roller packing a few weeks later to create a firm seed bed.  A third location was started in Kaysville, UT in early summer of 2010.  Mulch treatments included straw, wood chips, paper and no mulch.  Herbicide treatments included two organically certified herbicides; lemon grass oil (14% v/v) and clove oil (8% v/v).  Additional treatments included two rates of acetic acid (10% v/v and 15% v/v), pelargonic acid (7% v/v) and glyphosate (0.88 kg ae/ha).  Acetic acid does not contain a label but was included in the study because of wide spread use.  Mulches were applied July 15, 2009 at Logan and July 22, 2009 and April 19, 2010 at the Kaysville site for trial one and two, respectively.  Mulches were applied to an area 1.2 m wide by 42.7 m long.  Straw was applied at 15 cm thickness.  Wood chips were applied to a thickness of 6 cm.  Paper mulch was applied using a modified hydro seeder.  Paper was applied at 2178 kg/ha or 1 cm thickness.  Herbicides were applied using a CO2-pressurized backpack sprayer to 1.5 m wide and 6.1 m long sub-plots within each mulch.  All herbicide treatments except gylphosate were delivered at a spray volume of 561 l/ha at 278 KPa pressure through 8004 flat fan nozzles.  Glyphosate was applied in a spray volume of 187 l/ha except for 2 applications dates where it was applied at 561 l/ha.  Individual herbicides treatments were applied according to weed pressure, determined every 7 to 10 days.  Determination of which herbicides required additional applications was evaluated prior to spraying.  Herbicide applications were made two and three times in 2009 at Logan and Kaysville, respectively.  The following 2010 season herbicide treatments were applied a maximum of four times during the season at all three locations.  Percent weed control evaluations were made once a month.  Weed population densities were evaluated at the beginning of the season and at the end.  Weed biomass and weed percent cover were collected at the end of the 2010 season.  The straw mulch provided among the highest weed control and the least weed biomass at the end of the season in all locations.  Paper mulch provided the best weed control during the initiation year at all locations.  Paper mulch decreased in weed control effectiveness as the mulch would crack between wet and dry cycles that would allow weed seedlings to emerge.  Glyphosate and pelargonic acid gave near 100% weed control with all mulch treatments.  Wood chip mulch provided adequate weed control until late summer.  Late season weed control ratings in wood chip mulch provided little control compared to the no-mulch no-herbicide control treatment.  The two registered organic herbicides (lemon oil and clove oil) displayed the same weed control ratings and the same biomass results as the none-herbicide treatment in the three mulches (straw, wood chip, and paper).  Lemon oil and clove oil provided little weed control when applied without mulch.  While organically certified herbicides did not provide sufficient weed control alone, combinations of mulches with organic herbicides can provide adequate weed suppression. 




DETERMINE THE BENEFITS OF CANE BURNING TO RED RASPBERRY IN THE PACIFIC NORTHWEST. Y. Duan*1, T. W. Miller2; 1Washington State University, Pullman, WA, 2Washington State University, Mount Vernon, WA (50)

ABSTRACT

Chemical primocane management has become a common practice among Pacific Northwest raspberry growers. Given changes in cultivars, herbicides, and machine harvesters since its development during the 1970s, a study was initiated in 2010 to determine whether cane burning current Pacific Northwest raspberry cultivars still is a useful practice to improve berry harvest. The first trial was conducted with ‘Coho’ and ‘Meeker’ near Bow, WA and the second trial with ‘Meeker and ‘Cascade Bounty’ at the Washington State University Mount Vernon NWREC.

In the first trial, weed control with terbacil ranged from 88.8% to 97.4% in August, while control with oxyfluorfen or carfentrazone ranged from 51.3% to 70.3%. Carfentrazone initially suppressed primocane regrowth more than oxyfluorfen, but this became less obvious over time. In the second trial, oxyfluorfen suppressed initial primocane regrowth more in ‘Cascade Bounty’, while carfentrazone reduced primocane growth more in ‘Meeker’. There was a trend toward higher yield when a given cultivar was treated with carfentrazone or oxyfluorfen in either trial, but the increases were not statistically significant. However, when cultivar yields from the first trial were analyzed together, raspberries treated with oxyfluorfen alone or mixed with terbacil produced significantly more fruit (5402 and 5581 kg/ha, respectively) than non-treated raspberries (3989 kg/ha). Similarly, when cultivar yields were analyzed together in the second trial, both oxyfluorfen and carfentrazone increased berry yield (8000 kg/ha and 7321 kg/ha) compared to non-treated raspberries (6142 kg/ha). ‘Meeker’ was the top yielding cultivar overall, producing 5737 kg/ha berries in the first trial and 8107 kg/ha in the second trial, compared to 4369 kg/ha for ‘Coho’ and 6214 kg/ha for ‘Cascade Bounty’.




WEED MANAGEMENT OPTIONS FOR ORGANIC CANTALOUPE PRODUCTION. J. W. Shrefler1, C. L. Webber*2, M. J. Taylor1, B. Roberts1; 1Oklahoma State University, Lane, OK, 2USDA-ARS, Lane, OK (51)

ABSTRACT

Organic cantaloupe producers need weed control practices that will enable production of suitable yields of a quality crop.  Research was conducted in 2010 in southeast Oklahoma (Atoka County, Lane, OK) to compare several possible weed management strategies for growing cantaloupe.  Treatments included black plastic mulch, black woven landscape fabric, cultivation, flaming, Greenmatch herbicide as a directed spray, corn gluten meal applied in a band along side of the row, and Matran herbicide applied as a directed spray. The primary weeds included smooth crabgrass (Digitaria ischaemum  (Schreb.) Schreb. ex Muhl.), cutleaf groundcherry  (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus  L.) and yellow nutsedge (Cyperus esculentus L.).  At the 3 leaf crop stage vigor was assessed and all weed species were counted in all plots.  Yellow nutsedge was counted a second time 5 weeks later.  Crop vigor was greatest in the mulch, landscape fabric, and corn gluten meal treatments (85 to 90%) and ranged from 68 to 80% for other treatments.  The mulch and landscape fabric treatments reduced the populations of all weed species significantly.  Melons were harvested 4 times over a three week period.  Combined marketable yields across harvests ranged from 4500 to 8000 fruit per acre.  At the first harvest, yields were significantly greater in the mulch and fabric treatments, likely due to the soil warming effects of these treatments.  In summary, mulch and landscape fabric treatments provided best weed control, best early crop vigor, and greatest early yields.

 




TURF, WEED OR WEEDY TURF ? -- MY VIEW ON THE WEED TRANSFORMED FROM UNWANTED TURF GROWING IN CULTIVATED GOLF'S TURF. X. Guang*; East China Weed Technology Institute, Nanjing, Peoples Republic (52)

ABSTRACT

One kind of turf invaded into cultivated turf in golf course can be considered as an “invader” weed. The weed was a trouble to both golfer and superintendence of lawn maintenance. There were 15 kinds of the weed were found through 102 GOLF plots of China investigated during 1999 and 2009. 1) Weedy turf in bermudagrass (degeneration bermudagrass), 2) Bermudagrass in seashore paspalum, 3) Bermudagrass in zoysia grass, 4) Tall fescue in bermudagrass, 5) Seashore paspalum in bermudagrass, 6) Ryegrass in seashore paspalum, 7) Ryegrass in bermudagrass, 8) Seashore paspalum in zoysia grass, 9) Kentucky bluegrass in tall fescue, 10) Bentgrass in bermudagrass, 11) Tall fescue in kentucky bluegrass, 12) Bermudagrass in tall fescue, 13) Bentgrass in seashore paspalum, 14) Tall fescue in seashore paspalum and 15) Bentgrass in kentucky bluegrass. The weed was a kind of turf originally, but later became invasive and weedy. Therefore the weedy turf was transformed from unwanted turf growing in cultivated turf in golf plots. The author analyzed 5 aspects to which the weedy turf maybe harmful: public health (to add herbicide application), the appearance of golf course (color spot appeared in flush fairway and carpetlike green), performance of the golfer (to let golfer make mistaken in design of game-shots), cost of turf maintenance (to made weed control more difficulty) and turf lifespan (to renew the cultivated turf frequently). Meanwhile the author proposed 5 possible factors which may have caused the occurrence of weedy turf in golf: biological invasion, competition between unwanted and cultivated turf, herbicide resistance, climate change and improper application of herbicide. Seven strategies were proposed for controlling the weed: maintenance control, quarantine control, biological control, substitute control, predicting control and chemical control.

 

Nomenclature: Bentgrass:Agrostis stolonifera L.; Bermudagrass:Cynodon actylon×C.transvaalensis; Kentucky bluegrass:Poa pratensis L.; Ryegrass:Lolium perenne L.; Seashore paspalum:Paspalum viginatum Swart.; Tall fescue:Festuca arundinacea Schreb.; Zoysiagrass:Zoysia spp.

 




CORN GLUTEN MEAL RATE AFFECTS BROWN PATCH SEVERITY IN TALL FESCUE. A. Smith*, D. S. McCall, S. Askew; Virginia Tech, Blacksburg, VA (53)

ABSTRACT

Corn gluten meal (CGM) is a popular organic pre-emergent herbicide for crabgrass control. The by-product of corn processing, CGM is applied as a granular product in early spring. CGM suppresses root formation in germinating weeds, causing emerged weeds without developed root systems to die under moisture stress. The recommended application rate is 975 kg/ha, resulting in approximately 58% weed control.  However, for some, 58% control is insufficient and can lead to subsequent CGM applications later in the summer. Overapplication is a concern because CGM is 9% N by weight, and at the recommended rate of 975 kg/ha, provides approximately two times the maximum recommended spring N rate for cool-season turf. Excessive N can potentially promote turfgrass disease, such as brown patch (Rhizoctonia solani). Brown patch is considered one of the most troublesome turfgrass diseases in the United States and associated damage to turfgrass can decrease turfgrass competition with weeds by thinning the canopy. Research was conducted on tall fescue to determine if CGM rates affect brown patch severity. Trials were initiated in Blacksburg and Richmond, VA. Five rates of CGM [244 kg/ha, 488 kg/ha, 975 kg/ha, 975 kg/ha applied twice, and 975 kg/ha applied three times] were compared to identical N rates of a non-soluble synthetic N fertilizer and to no fertilizer to determine 1) brown patch response to N rate and 2) if CGM had any additional effect on brown patch severity. Disease severity, lesion counts, and turf color were recorded. Overall disease pressure was more severe in Richmond, VA where visual disease cover and lesion counts were higher. No differences were seen between CGM and synthetic N fertilizer. At both sites, there were no differences in lesion counts among treatments. In Richmond, differences were significant in disease severity ratings between the nontreated plots and plots receiving the highest amount of N. Nontreated plots had 30% brown patch cover, while plots receiving 975 kg/ha CGM applied three times had 51% brown patch cover. Turf color increased with increasing N rates in Richmond, but not in Blacksburg. These data suggest that the overuse of CGM for weed control can increase brown patch cover when conditions are favorable for disease and the disease-causing organism is present. Increased nitrogen likely resulted in more plant tissue growth, contributing to disease severity. The lack of differences in lesion counts, in contrast with the visual differences seen in disease ratings, may be due to an increased color contrast between the turf and brown patch. Moreover, highly fertilized plots may have had larger lesions with increased plant growth, thus accounting for differences in visual ratings.      



FIRE AND GRAZING INCREASE INVASIVE OPPORTUNITIES FOR SALT CEDAR IN THE PRAIRIE POTHOLE REGION. S. A. Clay*, M. Ohrtman, A. Smart; South Dakota State University, Brookings, SD (54)

ABSTRACT

Saltcedar (Tamarix spp.) typically colonizes freshly exposed moist soils following disturbances including overgrazing, fire, or flooding.  Although the seasonally wet conditions associated with the prairie pothole region (PPR) in the Northern Great Plains (NGP) appear uniquely suited for saltcedar, this area, unlike some areas of western South Dakota, has few infestations of this pervasive non-native.  Controlled burns and grazing are use to manage other invasive species (e.g. smooth brome, Bromus inermis and Kentucky bluegrass, Poa pratensis) in NGP rangelands.  These management techniques may inadvertently promote saltcedar invasion by opening the vegetative canopy.  Saltcedar establishment was investigated in fire, clipped (simulated grazing), and control (nonburned/nonclipped) treatments in NGP PPR soils.  Three soil cores per treatment were collected in spring immediately after fire treatment from three sites (one containing paired footslope and summit positions) in eastern South Dakota.  Cores were seeded with 100 saltcedar seeds in the greenhouse and subirrigated to maintain high soil water conditions typical near potholes during late spring/early summer.  In addition, a set of control cores were taken, seeded, and then burned under conditions (temperature and duration) that were typical of field burns.  Seedlings were counted every two d for 3 weeks to determine establishment. More saltcedar seedlings established in fire treatments (clipped or no clipped) (average 36 seedlings/core) compared with no fire/no clip controls (average of 11 seedlings/core).  Clipping without fire also increased seedling establishment (average 24/core) over the control treatment.  Burning after seed deposition resulted in few (<5 seedlings/core).  These results suggest that opening the canopy with fire or grazing increases the potential for saltcedar invasion.  Areas adjacent to viable saltcedar seed sources should be managed to maintain canopy cover to limit further saltcedar establishment. 




ECONOMIC ASSESSMENT OF INTEGRATED WEED MANAGEMENT PRACTICES USED TO IMPROVE FORAGE PRODUCTIVITY IN PASTURES. J. Tolson, J. Green*, K. Burdine, W. Witt, G. Schwab; University of Kentucky, Lexington, KY (55)

ABSTRACT

     Livestock producers with tall fescue based pastures often depend on mowing as the primary method for weed control.  In recent years interest in other weed management tools such as herbicide applications have increased.  Field research studies were initiated in 2008 and continued through 2010 on three grazed pasture sites within Kentucky to assess the economic value of mowing, herbicide treatment, and added fertility relative to the weed control and forage biomass produced.  Eight different treatments compared untreated plots with each main factor alone of mowing, herbicide application, and added fertility; and a combination of each of these factors including all three factors combined. At all locations, mowing was performed each year in July, herbicide treatment in mid-August, and added fertilizer in September.  Three subsample areas per plot were harvested in the spring 2009 and 2010 and botanically separated to determine treatment differences in forage grass yields, clover when present, and weed biomass. 

     Highest forage grass yields were obtained with herbicide plus fertilizer and the combination of mowing with herbicide and fertilizer.  At two of three sites total forage yield was also significantly higher with weed management practices that included herbicide alone or in combination with added fertilizer, or mowing with herbicide plus fertilizer.  Mowing alone increased forage yield compared to the untreated control at one location, was not different at another site, and produced less forage biomass at the third site. 

     At two of three sites the value of the forage produced for all treatments that included mowing, herbicide, added fertilizer, or any combination of these factors was equal or exceeded the forage value of untreated plots at two of three sites.  Furthermore, mowing alone, herbicide alone, and herbicide with fertilizer resulted in equal or higher net returns at these two sites. A positive net return was also obtained at one site with treatments that consisted of mowing with herbicide or mowing with herbicide and added fertilizer. At all sites the added value of forage produced by fertilizer alone was not enough to offset the cost of fertilizer.  At site three the net return was negative for all treatments since the added value of the forage produced relative to the untreated plots was less than the cost associated with added inputs.




ECOLOGY OF CUTLEAF TEASEL SEEDS. S. D. Eschenbach, G. O. Kegode*, D. B. Vlieger; Northwest Missouri State University, Maryville, MO (56)

ABSTRACT

Cutleaf teasel (Dipsacus laciniatus), a dicotyledonous forb commonly classified as a biennial and perennial, is present in twenty states and is deemed to be a noxious weed in Missouri, Iowa, Colorado, and Oregon. Cutleaf teasel is a rapidly-spreading invasive species, and often colonizes low-maintenance areas, such as roadsides. It has been suggested that early-maturing cutleaf teasel seeds germinating in the fall could achieve adequate rosette size (30 cm in diameter) to overwinter and bolt the following growing season, thus behaving as a winter annual. Preliminary data indicated a difference between the emergence rates of early and late maturing seed. This study was conducted to investigate the possibility of a difference in maximum percentage emergence between seed harvested in the months of August and November. Seeds were harvested from mature inflorescences at six locations of different mowing frequency across northwest Missouri during the months of August and November in 2008 and 2009. There was a total of 24 seedlots. Three repetitions of twenty seeds from each seedlot were sown in flats containing potting media, placed in a climate-controlled greenhouse (27 ± 2 C), and monitored for emergence during a period of approximately four weeks after seeding. The experiment was conducted twice. Statistical analysis detected highly significant effects for mowing frequency and mowing frequency by year interaction. Average cutleaf teasel emergence was 59, 69, and 65% for the not mowed, infrequently mowed, and frequently mowed regimes, respectively, for the 2008 harvested seeds, whereas it was 28, 39, and 57% for the 2009 harvested seeds, respectively. Averaged across locations, cutleaf teasel emergence was 88 and 54% for 2008 and 2009 August harvested seed, respectively, and was 40% and 28% for November harvested seed, respectively. The decreased dormancy demonstrated by the populations that were mowed frequently is especially apparent in the August seeds. This suggests that mowing may have led to the selection or development of populations of cutleaf teasel with decreased seed dormancy and potentially improved fitness to spread.




INCREASING NATIVE WARM SEASON GRASSES WITH FIRE, HERBICIDE, AND NITROGEN. S. M. Waughtel*; South Dakota State University, Brookings, SD (57)

ABSTRACT

Increasing Native Warm Season Grasses with Fire, Herbicide, and Nitrogen

S. Waughtel, S.A. Clay, A. Smart, D.E. Clay, and L.C. Schleicher

Plant Science, South Dakota State University, Brooking, SD

 

Native tallgrass prairie historically covered 260 million acres in the United States. The prairie has been reduced to only 3% of the original acreage due to farming practices, introduction of exotic plants, and loss of natural interactions with buffalo and fire. Native species are often outcompeted for nutrients, water, and light by non-native plants causing a loss in diversity of the remaining prairie. This study examines the use of prescribed burns, glyphosate, and nitrogen application at specific stages of plant growth to reinvigorate native species and suppress invasive species. Two South Dakota locations containing a mix of native [big bluestem (Andropogon gerardii) and blue grama (Bouteloua gracilis)] and exotic, non-native species [smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis)]. Plots were treated then evaluated twice at the height of growth for cool-season and warm-season grasses. Prescribed burn plots had double the warm-season biomass and cool-season grass biomass was reduced by 50% when glyphosate and April nitrogen were applied. Photosynthetic capacity was also measured by crop scan. Continued field work includes a second year treatment and evaluation.

Organisms: big bluestem (Andropogon gerardii), sideoats (Bouteloua curtipendula ), smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis)

Herbicides: glyphosate (32 oz./acre fall treatment, 8 oz./acre spring rate)




RUSSIAN KNAPWEED MANAGEMENT IN SOUTHWESTERN ABANDONED PASTURES. W. B. McCloskey*1, K. McReynolds2, E. Foster3, D. Arthun4; 1University of Arizona, Tucson, AZ, 2University of Arizona, Willcox, AZ, 3NRCS USDA, Safford, AZ, 4BLM, Safford, AZ (58)

ABSTRACT

The efficacy of herbicide treatments on Russian knapweed was investigated in infested abandoned pastures in 2009 and 2010 in Kansas Settlement and Duncan in Southeastern Arizona. The experiments utilized a randomized complete block design; at Kansas Settlement plot size was 6.6 m by 58 m with three replications and at Duncan the plot size was 6.6 m by 12.2 m with four replications. A second, smaller experiment at Duncan was replicated 4 times with a plot size of 3 m by 6 m. The plots in Kansas Settlement and Duncan were subsampled 40 and 8 times, respectively, using either a 0.16 m square or 0.25 m square depending on the date to determine the density of Russian knapweed shoots. At Kansas Settlement, herbicides were applied on June 22, 2009 when the mean number of shoots was 11.8 green shoots/m2 and on December 18, 2009 when the mean was 9.7 dormant shoots/m2. The herbicides, aminopyralid at 87 and 122 g/ha, aminocyclopyrachlor plus chlorsulfuron at 70 plus 26 g/ha, respectively, and 140 plus 52 g/ha, respectively, picloram at 560 g/ha and chlorsulfuron at 93 g/ha were applied with a methylated seed oil at 1% v/v using a tractor mounted sprayer travelling at 3 MPH and TeeJet TT1103 nozzles at 25 PSI resulting in a carrier volume of 20 GPA. Russian knapweed shoots were counted again on May 13, 2010 and phytotoxicity was visually assessed on September 13, 2010. Russian knapweed shoot densities in the order of the herbicides listed above in plots treated on June 22, 2009 were 1.53, 0.80, 0.04, 0.07, 0.66, and 2.09 shoots/m2 on May 13, 2010 compared to 14.6 shoots/m2 in the untreated control 11 MAT (months after treatment). The corresponding visual phytotoxicity ratings on September 13, 2010 were 90, 94, 99, 99, 93, and 0% compared to the untreated control (0%) 15 MAT. Similarly, Russian knapweed shoot densities in the order of the herbicides listed above in plots treated on December 18, 2009 were 0.07, 0.0, 0.0, 0.0, 0.1, and 0.04 shoots/m2 on May 13, 2010 compared to 14.6 shoots/m2 in the untreated control 5 MAT. All of the herbicide treatments were statistically different than the untreated control plots but were not different from one another with the exception of the chlorsulfuron treatment where the Russian knapweed population recovered from the initial suppression. In the Duncan experiment, herbicides were applied on December 17, 2009 when the mean number of shoots was 37.7 shoots/m2. The herbicides, aminopyralid at 87 and 122 g/ha and picloram at 560 g/ha were applied with a methylated seed oil at 1% v/v using a tractor mounted sprayer as described for the Kansas Settlement experiment. Russian knapweed shoot densities in the aminopyralid at 87 and 122 g/ha and picloram at 560 g/ha treatments were all 0.0 on May 14, 2010 compared to the untreated control density of 31 shoots/m2. Similarly, the visual phytotoxicity ratings were 100% on June 29, 2010 compared to the untreated control (0%). In the smaller Duncan experiment, imazapyr was applied at 0.56 and 0.84 kg ae/ha with a CO2 pressurized backpack sprayer using parameters similar to the tractor mounted sprayer on December 17, 2009 when the initial Russian knapweed stem density was 39 shoots/m2. The following spring the stem densities were 0, 0 and 68 shoots/m2 in the imazapyr at 0.56 kg ae/ha, imazapyr at 0.84 kg ae/ha and the untreated control treatment, respectively. These data indicate the aminopyralid, aminocyclopyrachlor, picloram and imazpyr were all effective as dormant (i.e., preemergence) herbicide treatments for Russian knapweed during the winter of 2009-2010 in Southeastern Arizona. It should be noted that the 2009-10 winter was characterized by above normal rainfall, particularly in the spring. Additional herbicide treatments were applied in the spring of 2010 and all of the treatments applied to date will be reassessed again in 2011.




INFLUENCE OF SPRING APPLICATIONS OF AMINOPYRALID PLUS METSULFURON ON FORAGE CHARACTERISTICS AND BEEF STEER PERFORMANCE IN MISSOURI PASTURES. T. R. Legleiter*, J. Sexten, C. Roberts, K. W. Bradley; University of Missouri, Columbia, MO (59)

ABSTRACT

Spring applications of some metsulfuron-containing herbicides are known to cause stunting and yield reductions in tall fescue pastures. However, little research has been conducted to investigate the potential for spring treatments of metsulfuron-containing herbicides to reduce tall fescue seedhead production and ergovaline content and thus increase average daily gain in cattle grazing tall fescue pastures. Grazing experiments were conducted near Columbia, Missouri during the summer of 2010 to investigate the effects of spring treatment of aminopyralid plus metsulfuron plus 2, 4-D on forage yields, tall fescue seedhead production, and beef steer performance. On April 1, either aminopyralid plus metsulfuron plus 2, 4-D at 0.09 plus 0.01 plus 1.1 kg/ha, respectively, or 2, 4-D at 1.1 kg/ha were applied to 3 endophyte-infected and 3 endophyte-free 1-ha paddocks.  Five 217 ± 17.9 kg crossbred steers were turned out to graze each paddock for 78.4 ± 5.5 days following treatment. Grazing began when 2,242 kg dry matter per ha was available to steers as estimated with a rising plate meter.  Resulting grazing initiation was 9.3 days later for pastures treated with aminopyralid plus metsulfuron plus 2, 4-D.  Monthly forage yields, forage grass seedhead production, and average daily gain (ADG) of beef steers were determined for three months following application. Forage yields were reduced in response to applications of aminopyralid plus metsulfuron plus 2, 4-D compared to applications of 2, 4-D alone at all monthly intervals after application. Across all three months of the research, cumulative forage yields were reduced by 52% in pastures treated with aminopyralid plus metsulfuron plus 2, 4-D compared to 2, 4-D alone. Aminopyralid plus metsulfuron plus 2, 4-D reduced tall fescue seedhead density by 61% compared to 2, 4-D alone but had no affect on orchardgrass or Kentucky bluegrass seedhead density. There was no effect of herbicide treatment (P=0.47) or endophyte infection level (P=0.07) on average daily gain of beef steers. However, the percentage of cattle exhibiting a slick hair coat was 28.6% greater in cattle grazing paddocks treated with aminopyralid plus metsulfuron plus 2, 4-D compared to 2, 4-D alone. By September, paddocks treated with aminopyralid plus metsulfuron plus 2, 4-D contained approximately 3 and 5 times more yellow foxtail and large crabgrass, respectively, than paddocks treated with 2, 4-D alone. Results from this experiment revealed that treatment with aminopyralid plus metsulfuron plus 2, 4-D delayed the onset of grazing, reduced forage and tall fescue seedhead production, increased invasion of summer annual grass weeds, improved coat shedding, and resulted in similar individual ADGs compared to 2,4-D alone when stocked at a set stocking rate. 

 




THE SAFETY AND EFFICACY OF MESOTRIONE IN LONGLEAF PINE SEEDLINGS. M. A. Czarnota*; University of Georgia, Griffin, GA (60)

ABSTRACT

Reforesting with longleaf pine (Pinus palustris) is becoming very popular in the Southeast. Longleaf pine establishment is much better if plug plants are used in place of bare-root seedlings. Producing longleaf pine in a soilless media, however, creates new weed control challenges. One of the biggest concerns is herbicide damage to the seedling pines. To address these concerns, an experiment was initiated in April of 2010 to evaluate select herbicides on longleaf pines in a soilless media. Callisto® (mesotrione) and GoalTender® (oxyfluorfen) and were evaluated. Callisto was applied at 1, 2, 4, and 8 oz pr/A, and GoalTender was applied at 1, 2, 4 pt pr/A and sequentially at 1 and 2 pt/A. Herbicides were applied at seeding, and the sequential application of GoalTender was applied after seedlings had hardened off. At 16 WAT, no significant injury was seen on the longleaf pines with any of the treatments. Also, there was no significant reduction in germinated pines with any of the treatments of Callisto and GoalTender at 16 WAT. Spotted spurge (Euphorbia maculate) was the only weed present in the study, and control was significantly better with all treatments of Callisto and GoalTender 16 WAT. More research is needed to determine the safety of both Callisto and GoalTender to different pine species, and to determine the timing and rates that these herbicides can be applied.




USING A PLANT DISPERSAL MODEL FOR YELLOW STARTHISTLE FOR LANDSCAPE LEVEL WEED MANAGEMENT PLANNING. L. W. Lass*1, T. Prather1, B. Shafii1, S. Cook1, T. Venn2, W. Chung2, S. R. Radosevich3, P. Aracena2, W. J. Price1, C. Crabtree4, P. Green5, S. Kesoju1; 1University of Idaho, Moscow, ID, 2University of Montana, Missoula, MT, 3Oregon State University, Corvallis, OR, 4Idaho County Weed Superintendent, Grangeville, ID, 5USFS, Grangeville, ID (61)

ABSTRACT

Managing multiple invasive species across extensive areas is challenging and would benefit from a landscape-level decision support tool. This project develops tools to forecast the optimal type of treatment and spatial placement (cost) into the future, allowing the comparison to other strategies including no treatment. Forecasting five years into the future also requires predicting changes to the invasion process. The project explores a short-distance dispersing weedy species, yellow starthistle, a long-distance wind dispersing weedy species, rush skeletonweed and a short-distance dispersing insect, balsam woolly adelgid. The specific research objectives are: 1) Model dispersal of three invasive species using network models that utilize species occurrence, plant community biomass and climate data; 2) Estimate fixed and marginal costs of alternative invasive species management programs, and market and non-market damages (costs) of invasive species; 3) Expand an existing decision-support system to integrate ecological and economic information, so that optimal invasive species management programs may be determined. Logistic Regression models were developed to predict the likelihood of occurrence for these three pests in Idaho. Development of spatial network models for yellow starthistle and balsam wooly adelgid were developed to predict short-distance dispersal. Improved wind dispersal modeling for rush skeletonweed is in progress. These models will estimate spread rates in order to allow economic evaluation of management strategies. Results will assist in landscape management of invasive species.




USE OF ENDOTHALL FOR CONTROL OF EURASIAN WATERMILFOIL IN IRRIGATION CANALS. J. D. Vassios*1, S. J. Nissen1, C. J. Gray2; 1Colorado State University, Fort Collins, CO, 2United Phosphorous, Inc., Peyton, CO (62)

ABSTRACT

Although Eurasian watermilfoil (Myriophyllum spicatum) (EWM) is commonly found in lakes and ponds, it can prove especially difficult to control in flowing water systems. Endothall is labeled for EWM control, and in 2010 two endothall formulations, dipotassium salt (DPSE) and the mono(N,N-dimethlalkylamine) salt (MSE), were approved for use in irrigation canals.  While DPSE will only provide control of aquatic weeds, MSE can also provide algae control.  While these herbicides have been shown to provide good control of sago pondweed (Stuckenia pectinata) in flowing water systems, little work has been done to examine EWM efficacy in these situations.  During Summer 2010, two field-scale demonstration studies were conducted.  The first site was the Leggett Canal near Boulder, CO, which contained EWM, sago pondweed, and elodea (Elodea canadensis).  The second site was the Minnequa Canal that originates outside of Florence, CO, which contained only EWM.  Herbicides combinations were to the Leggett Canal (2.75 ppm DPSE + 0.25 ppm MSE for 8 hours) and the Minnequa Canal (1.8 ppm DPSE + 0.2 ppm MSE for 12 hours).  Water samples were taken during treatment to confirm application rates.  Following herbicide applications, both canals were monitored with visual ratings and photographs over 28 DAT.  EWM control was >80% at both sites and nearly 100% control of sago pondweed and elodea was observed at the Leggett Canal.  Both sites will continue to be monitored during 2011 to evaluate residual control.




WATER LETTUCE AND WATER HYACINTH CONTROL USING SAFLUFENACIL. J. D. Vassios*, S. J. Nissen; Colorado State University, Fort Collins, CO (63)

ABSTRACT

Water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes) are floating aquatic species that occur mainly in the southern United States.  These species can negatively impact water quality, water flow, light infiltration and provide habitat for pest insects.  There are many systemic and contact herbicides that can be used for control of both species.  Saflufenacil is a new herbicide currently registered primarily for broadleaf weed control in agricultural systems.  During the summer 2010, a greenhouse study was conducted at Colorado State University to evaluate safluenacil (25 and 50 g ai/ha) applied alone and in combination with labeled aquatic herbicides for water hyacinth and water lettuce control.  Other herbicides included were: glyphosate (2,214 g ae/ha), imazamox (140 g ai/ha), triclopyr (840 g ae/ha) and 2,4-D amine (2,130 g ae/ha).  Three plants of each species were placed in 18 L containers and foliar treatments applied using a 187 L/ha application volume.  Following treatment, plants were maintained in the greenhouse for 58 days.  Visual control ratings were taken at 3, 8, 16, 30, and 58 DAT.  In addition to visual evaluations, photos were taken at 58 DAT.  Saflufenacil (50 g ai/ha) applied alone provided 52% and 80% control 58 DAT for water lettuce and water hyacinth, respectively.  Saflufenacil tank mixed with glyphosate provided the best control of water lettuce.  Glyphosate applied alone and saflufenacil tank mixed with glyphosate or 2,4-D amine resulted in the best water hyacinth control; however, treatments containing saflufenacil exhibited faster burndown than glyphosate or 2,4-D amine applied alone.  When glyphosate was applied with saflufenacil (50 g ai/ha), 90% control was reached by 16 DAT, compared to 30 DAT with glyphosate only.




THE EFFECT OF SELECTED HERBICIDES ON GROWTH AND HYDROCARBON CONTENT OF BOTRYOCUCCUS BRAUNII K¨šTZING BERKELEY STRAIN (VAT. SHOWA). L. Deng*, S. A. Senseman, T. Gentry, D. Zuberer, T. Weiss, T. Devarenne, E. R. Camargo; Texas A&M University, College Station, TX (64)

ABSTRACT

Botryococcus braunii, one of the potential renewable resources for production of liquid hydrocarbons cultures, was used for testing the effect of different herbicides on the growth and hydrocarbon content. Diuron was the most toxic herbicide for algal growth, whereas hydrocarbon content increased to 42% in a 0.1 mg/L concentration of diuron. Diquat was inhibitory on growth of B. braunii, and the effect increased with increasing concentration. The hydrocarbon content was 26% in 0.1 mg/L diquat, and 43% in 5 mg/L diquat. S-metalochlor at 0.1, 1, and 5 mg/L decreased hydrocarbon content to 16, 14 and 6% respectively. S-metalochlor reduced algal growth and algal oil yield. Fluridone at 0.1 mg/L did not affect algal growth, but decreased hydrocarbon from 35% to 13%. Thiobencarb at 0.1 mg/L did not affect algal growth and oil content, but at 1 mg/L inhibited algal growth and reduced hydrocarbon decreased from 35% to 8%. Dinoterb at 0.1 mg/L reduced algal biomass and hydrocarbon content. Accelerated Solvent Extraction (ASE) was used to extract oil from algae and was effective for extracting algal oil with optimized temperature at 50°C and 1 extraction cycle with hexane.




MONOECIOUS HYDRILLA CONTROL WITH ENDOTHALL OVER TWO YEARS. S. Meadows*, J. J. Nawrocki, R. J. Richardson; North Carolina State University, Raleigh, NC (65)

ABSTRACT

Field research was conducted on a 620 ha North Carolina impoundment to quantify the effect of endothall and herbicide combinations containing endothall on monoecious hydrilla.  In 2009, herbicide treatments were applied (later than desired) to topped-out hydrilla during late August. Five treatments were applied through four weighted trailing hoses to 3.08 ha m-1 sections of separate coves of the impoundment.  Herbicide placement was approximately 0.75 m below the water surface.  Treatments included endothall alone at 2 and 3 mg ai l-1, endothall at 1 mg ai l-1  plus diquat at 0.368 mg ai l-1, endothall at 2 mg ai l-1  plus diquat at 0.368 mg ai l-1, and endothall at 2mg ai l-1  plus copper at 0.5 mg ai l-1. A nontreated cove was also monitored during the study for comparison.  In 2010, herbicide treatment was more timely and applied to 0.5 m tall hydrilla during late June.  Due to the efficacy observed in 2009, each herbicide treatment was applied at 50% of the application rate used in 2009.  In both years, biomass samples were collected pretreatment and at 2, 4, and 8 weeks after treatment (WAT) using a weed harvest rake with a collection area of 700 cm2.  Soil core samples were also collected pretreatment and at the end of the growing season in each experimental area to determine any treatment effects on subterranean turion (tuber) density.  A 10 cm diameter core sampler was used to extract samples to a depth of 20 cm.  Samples were then sifted to separate tubers from sediment and allow quantification.  In 2009, all treatments reduced hydrilla biomass by at least 95% at 8 WAT from that of the nontreated dry weights, but no differences were present between herbicide treatments.  However, tuber numbers were not reduced after treatment.  In 2010 at 8 WAT, all treatments again reduced hydrilla biomass by at least 95% from that of the nontreated  and tuber numbers were also generally not lower than pretreatment levels.  In conclusion, endothall alone or in combination with diquat or copper was extremely effective in reducing hydrilla biomass whether applied in a timely manner or not.  The reason for lack of treatment effect on tuber numbers is unknown, but future research should evaluate the temporal formation of tubers by hydrilla in relation to application timing.



MULTI-YEAR SURVIVAL, GROWTH AND MATURATION OF INVASIVE SWALLOW-WORT JUVENILES (VINCETOXICUM SPP.) ACROSS A HABITAT GRADIENT. L. R. Milbrath1, A. DiTommaso*2, J. Biazzo1, S. H. Morris2; 1USDA-ARS, Ithaca, NY, 2Cornell University, Ithaca, NY (66)

ABSTRACT

Vincetoxicum rossicum, pale swallow-wort [PSW], and V. nigrum, black swallow-wort [BSW] are two non-native perennial vines that are increasingly problematic in many regions of the northeastern US and southern Canada.  The two species can grow in full sun or shaded forest understories, and infest a variety of habitats from agricultural to natural areas. Seedling establishment and growth may be an especially critical phase in the life cycle of plants and may be targeted for control of invasive species if this stage is important for population growth. We established a long-term field experiment in fall of 2007 to assess survival and growth of early-stage swallow-worts in three different habitat types: an old field [high light], a forest edge [transition zone] and forest understory [low light] at a central New York State location where both species are present in the region although not at the experimental site.  The two swallow-wort species were established from seed in a split plot design with habitat type as the whole plot treatment, swallow-wort species as the subplot treatment, and 10 blocks for a total of 60 subplots.  From an initial cohort of 40 seedlings per subplot, survival and growth (i.e. height, time to first flower, seed production) of these seedlings have been monitored annually.  After the third season of growth (2010), survival of black swallow-wort (31±4%) was greater than pale swallow-wort (6±2%). Survival of juvenile BSW plants was greater in the forest edge habitat (77±5%) than forest understory (49±6%) but not the old field (58±6%). Survival of PSW plants was similar among the forest edge (42±6%), old field (34±6%) and forest understory habitats (37±6%).  Juvenile BSW plants remained 2.5-3.5 times taller than PSW in all habitats with the greatest differences in height between the species observed in the old field habitat. Since the start of the field study, only four BSW plants have flowered (one in 2009 and three in 2010), but none of the plants produced seed.  The relatively low seedling establishment levels observed in this study especially for PSW are surprising given that this species typically thrives in high light, open habitats in the region.  However, the dense cover of resident vegetation in the old field may have suppressed PSW establishment and growth more than the larger seeded BSW.  Also, this research confirms the suitability of forest-old field transition zones (ecotone) for establishment and growth of these two swallow-wort species and suggests that management tactics be especially targeted in this habitat.




SMALL MAMMAL RESPONSE TO CHINESE PRIVET REMOVAL FROM RIPARIAN FORESTS IN NORTHEAST GEORGIA. M. S. Murphy*, S. B. Castleberry; University of Georgia, Athens, GA (67)

ABSTRACT

     

Chinese privet (Ligustrum sinense) is an invasive plant commonly found along riparian forests throughout Northeast Georgia.  Its dense evergreen foliage often creates a monoculture by outcompeting other vegetation.  Our objective was to determine if small mammal populations differed among two privet removal treatments and a control.  Removal treatments were applied in 2005 and consisted of 1) mulching followed by glyphosate application, and 2) felling followed by a glyphosate application.  Each treatment and control were applied at four locations.  We sampled small mammals in 2006 and 2010 using Sherman collapsible live traps and compared relative abundance among treatments.  We captured 134 unique individuals representing three species in 2006 and 50 unique individuals representing five species in 2010.  In 2006, captured species included the white-footed mouse (Peromyscus leucopus), golden mouse (Ochrotomys nuttalli), and house mouse (Mus musculus).  In 2010, in addition to the white-footed and golden mice, we captured rice rats (Oryzomys palustris) , hispid cotton rats (Sigmodon hispidus), and short-tailed shrews (Blarina brevicauda).  We found no significant differences in relative abundance (captures / 100 trap nights ±SE) among treatments, seasons, or the treatment x season interactions for either year, although capture numbers were higher in the treated plots.  From these findings, the treatments did not have a negative effect on populations of small mammals. 




NATIVE AND INVASIVE RUBUS HYBRIDIZE TO PRODUCE APOMICTIC OFFSPRING. L. V. Clark, M. Jasieniuk*; University of California, Davis, Davis, CA (68)

ABSTRACT

 Microsatellites distinguish sexual versus apomictic reproduction in spontaneous blackberry (Rubus) hybrids.

Lindsay V. Clark and Marie Jasieniuk

Department of Plant Sciences, University of California - Davis

Reproductive mode plays an important role in the evolution of new invasive species following hybridization events.  Asexual reproduction can maintain the high fitness associated with heterosis, whereas sexual reproduction produces a greater number of novel genotypes and allows for local adaptation to occur.  In previous work, we identified spontaneous hybrids between the native California blackberry (Rubus ursinus) and invasive Himalayan blackberry (R. armeniacus) and between California blackberry and the non-native Pennsylvania blackberry (R. pensilvanicus). California blackberry is a sexual, outcrossing species and is the female parent of these hybrids, whereas Himalayan blackberry and Pennsylvania blackberry, the male parents, are pseudogamous apomicts (producing approximately 90% of seed asexually but requiring pollination to do so).  In the present study, we determine the reproductive mode of the spontaneous hybrids by analyzing genotypes of seeds and seedlings at five microsatellite loci.  Each offspring was assigned a score based upon extra or missing alleles with respect to the mother plant, and the distribution of scores was used to distinguish sexual and asexual progeny.  Most seeds produced by R. ursinus x pensilvanicus are produced asexually, whereas seeds of R. ursinus x armeniacus are produced by approximately equal amounts of sexual reproduction and apomixis.  However, in both cases, a disproportionately high number of the seeds that germinated were sexually produced, indicating a low viability for apomictic seed.  Fixed heterosis is therefore unlikely to contribute to invasiveness in these hybrids, but hybrid populations may continue to evolve by sexual recombination.  Blackberry populations containing hybrids of native and non-native species should be periodically monitored in case management becomes necessary to prevent the spread of new invasive forms.
 
mjasien@ucdavis.edu




HYBRIDIZATION AND INVASION: USING MOLECULAR PHYLOGENETIC METHODS TO REVEAL THE ORIGINS OF NORTH AMERICAN FRENCH BROOM INVASIONS. A. C. Kleist*, M. Jasieniuk; University of California, Davis, Davis, CA (69)

ABSTRACT

Evidence of hybridization among ornamental plants and naturalized populations is important because such hybridization can increase invasiveness and make management, particularly biological control, difficult.  French broom, hypothesized to be Genista monspessulana, was introduced into California by the horticultural industry and has caused serious environmental damage throughout the state.  It is no longer available commercially, but its close relative, sweet broom, is a popular ornamental and may be contributing to invasive populations.  The goals of this research are to: i) identify the cultivated sources of invasive broom populations in California, and ii) determine whether hybridization between ornamental plants and naturalized populations has occurred.  To address these objectives, we collected samples from invasive French broom populations throughout California, landscape plantings, horticultural outlets, and botanical gardens and arboreta from its native range.  These samples were used to reconstruct a phylogeny of brooms using two chloroplast and two nuclear DNA regions.  We also cloned nuclear ITS sequences to confirm parentage and assess hybrid origin.  ITS sequences are non-coding DNA regions that occur several hundred times throughout the genome.  The copies are usually homogenized so that only a single sequence is found within an individual.  However, this homogenization process may not be complete in recent hybrids.  Thus, analyzing multiple copies of ITS from suspected hybrids can give information about parentage and hybrid origin. 

Phylogenetic analyses revealed a well-supported group containing G. monspessulana samples from its native range and the majority of invasive French broom samples from California.  ITS phylogenetic analysis including the additional sequences from cloning experiments revealed an ornamental sweet broom group containing sequences from seven invasive French broom populations.  Our results suggest that the majority of invasive French broom in California originated from G. monspessulana but that ornamental sweet broom can contribute to invasive populations directly and via hybridization.  




MANAGEMENT OPTIONS FOR JAPANESE STILTGRASS (MICROSTEGIUM VIMINEUM) IN NATURAL AREAS. T. L. Mervosh*1, J. S. Ward2, J. P. Barsky2; 1Connecticut Agricultural Experiment Station, Windsor, CT, 2Connecticut Agricultural Experiment Station, New Haven, CT (70)

ABSTRACT

Japanese stiltgrass (JSG) is an annual grass species native to eastern Asia.  A serious invasive plant problem in the eastern United States, JSG has expanded its range greatly in southern New England in recent years.  Because JSG grows well in low light conditions, it tends to invade and dominate the ground layer of forests.  We conducted a study in a woodland along the Connecticut River in East Haddam, CT.  The site is infested with JSG, which is displacing native plant seedlings.  In Connecticut, JSG seedlings begin to emerge in April, and plants typically produce seeds in September. 

We evaluated several non-chemical and herbicide treatments for efficacy in controlling JSG and impacts on other vegetation.  Four blocks of eighteen 3- by 4-meter plots were established in May 2008.  Each treatment was assigned randomly to one plot per block.  Treatments were applied on June 11, July 25 and August 29, 2008, and on June 10, July 23 and August 20, 2009.  Each plot was treated once per year, with the same treatment applied in the same month both years.  Treatments included flaming with a propane torch (directed heat) [June and July timings], pulling JSG by hand [July], and cutting with a string trimmer [July and August].  In addition to foliar application of household vinegar (5% acetic acid content, undiluted) [June and July], the following herbicides were applied at doses according to product labels:  ammonium salt of imazapic (0.14 kg acid equivalent [ae] per hectare) [June], pelargonic acid (11.8 kg ae ha-1) [June and July], and pelargonic acid (11.8 kg ae ha-1) + pendimethalin (3.36 kg active ingredient [ai] ha-1) [June].  The following herbicides were applied at labeled doses and at one-fourth labeled doses:  fenoxaprop-p-ethyl (0.18 and 0.045 kg ai ha-1) [July], glufosinate-ammonium (0.56 and 0.14 kg ai ha-1) [August], and isopropylamine salt of glyphosate (0.56 and 0.14 kg ae ha-1) [August].  Not all of these herbicides are registered for use in natural areas (check product labels for approved sites).  Herbicides were applied with a calibrated, three-nozzle spray boom (8003VS flat-fan tips) pressurized with CO2.  Spray volume was 234 liters per hectare, except 468 L ha-1 for vinegar and pelargonic acid treatments.  A non-ionic surfactant (0.25% v/v) was added to each spray bottle. 

Plots were evaluated periodically for JSG stand density (% area covered), height and vigor, in addition to JSG seed production and effects on other plants.  Above-ground JSG parts, including seeds, were collected from sample points within plots in October 2008 and 2009.  Final evaluations were taken in June 2010.  End-of-season JSG stand density in untreated plots was about 90% in 2008 and 2009.  All treatments reduced JSG coverage and seed production.  The least effective treatments were hand-pulling, pelargonic acid, and vinegar in July.  Flaming, string trimming, and vinegar in June reduced seed production by more than 90%.  All treatments containing imazapic, pelargonic acid + pendimethalin, fenoxaprop, glufosinate and glyphosate completely prevented JSG seed production in 2008 and 2009.  Plots in which no seeds or very few seeds were produced in 2008 had much lower emergence of JSG seedlings in 2009 compared to untreated plots, suggesting most seedlings originated from seeds shed the previous year.  Preventing seed input into the soil is a key component to a successful JSG management program.  In June 2010, native plant cover data was collected; plots that had been string trimmed or sprayed with vinegar in June, pelargonic acid (alone) or fenoxaprop treatments in previous years had the highest percentage of native plants.  Several non-chemical and herbicide treatments are effective at controlling JSG.  Ecological, economic and site-use issues must be considered in determining a management strategy for Japanese stiltgrass.




CHANGES IN THE WEED SPECIES COMPOSITION OF THE SOUTHERN US: 1995 TO 2010. T. M. Webster*1, R. L. Nichols2; 1USDA-ARS, Tifton, GA, 2Cotton Incorporated, Cary, NC (71)

ABSTRACT

Changes in the weed flora of crops reflect not only the influx and loss of propagules in the soil reserve, but also the management impacts of the crops grown, the tillage employed, and the herbicides applied.  This analysis documents the changes in the weed flora of the 14 contiguous states comprising the Southern Weed Science Society (SWSS) since the advent of transgenic, herbicide resistant crops, and relates these changes to management factors using the available data.  Each year the SWSS solicits data from expert weed scientists from their respective states on the common and difficult-to-control weeds that occur in their crops.  The data are collected on a four-year rotation on weeds in broadleaf crops; grass crops; vegetable, fruit, and nut crops; aquatic environments, industrial areas, nursery and container ornamentals, and rights-of-way.  The data received are complied and reported in the Proceedings of the SWSS Annual Meeting. National statistics for crop hectares are collected annually by the U. S. Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) and reported for crops by state at www.nass.usda.gov.  Data for herbicides are collected annually, but only selected crops reported each year http://USDA.mannlib.cornell.edu.  We evaluated changes in applications by area for each crop between 1990 and 2005 (wheat), 1990 and 2006 (corn and soybean), and 1990 and 2007 (cotton). The SWSS surveys of 1994 and 2008 were compared for corn and wheat and surveys of 1995 and 2009 compared for cotton and soybean.  The relative ranking of each species was weighted based on the number of states listing it among the 10 most troublesome weeds, as was previously done when comparing the changes in species composition between 1974 and 1994/1995.

 

In soybean (Glycine max), morningglories (Ipomoea spp.), nutsedges (Cyperus spp.), and sicklepod (Senna obtusifolia) were among the top five weed species in 1995 and 2009. Palmer amaranth (Amaranthus palmeri) and horseweed (Conyza canadensis) were the second and fourth most troublesome weeds of soybean. Horseweed, Florida pusley (Ricardia scabra), Benghal dayflower (Commelina beghalensis), and groundcherries (Physalis spp.) had the largest increases in troublesomeness.   Acetolactate synthase (ALS) inhibiting (up to 89% of the hectares treated) and dinitroaniline DNA’s (up to 58%) herbicides were the dominant classes before transgenic cultivars. Glyphosate was applied to 96% of  soybean hectares in 2006, while ALS (5%) and DNA (1%) applications substantially declined.

 

In cotton (Gossypium hirsutum), morningglories and nutsedges were among the top five most troublesome weeds in 1995 and 2009. Palmer amaranth, pigweeds (Amaranthus spp.), and Florida pusley were also listed among the five most troublesome species in 2009. The weeds with the largest increase in importance were Benghal dayflower, Florida pusley, and common ragweed (Ambrosia artemisiifolia).  Before glyphosate-resistant cotton, Photosytem II (PSII)-inhibitors (up to 93%) and DNA’s (up to 83%) were the dominant herbicide classes applied to cotton. While they are still applied to 37 to 46% of cotton hectares, glyphosate was applied to 93% of the cotton area.

 

In corn (Zea mays), the top five weeds in 2008 were morningglories, Texas millet (Urochloa texana), broadleaf signalgrass (Urochloa platyphylla), johnsongrass (Sorghum halepense), and sicklepod. These same weeds were the top five in 1994, but johnsongrass was the most troublesome. The species with the greatest increase in corn were Palmer amaranth, smartweeds (Polygonum spp.), and goosegrass (Eleusine indica).  PSII-inhibitors continue to be the dominant herbicide class used in corn, though glyphosate applications increased to include over 30% of the corn area in 2006 and estimates suggest this value approached 60% in 2010.

 

In wheat (Triticum aestivum), the top four weeds in 2008 were the same as in 1994 and include Italian ryegrass (Lolium perenne ssp. multiflorum), wild garlic (Allium vineale), wild radish (Raphanus raphanistrum), and henbit (Lamium amplexicaule). The number five weed and species that increased most in importance was annual bluegrass (Poa annua). Phenoxy (up to 72%) and PSII (46%) herbicides remain the predominant tools used in wheat, though glyphosate use has increased to 20% of the area as of 2006.




CREATING A PHOTOGRAPHIC GUIDE TO IDENTIFY HERBICIDE DRIFT IN RICE. J. B. Hensley*1, E. P. Webster1, B. Schultz2; 1LSU AgCenter, Baton Rouge, LA, 2LSU AgCenter, Crowley, LA (72)

ABSTRACT

Four studies were conducted at the LSU AgCenter Rice Research Station near Crowley, Louisiana to evaluate the physiological effects of simulated herbicide drift on ‘Cocodrie’ rice. The objective of these studies was to observe and photographically document the visual symptoms expressed in susceptible rice when exposed to sub-lethal doses of the herbicides glyphosate, imazethapyr, glufosinate, and imazamox. It was observed that the translocated herbicides glyphosate, imazethapyr, and imazamox resulted in differing visual symptoms when applied at vegetative compared with reproductive growth stages. The herbicide glufosinate, with more contact activity, generally resulted in only foliar injury near the site of droplet deposition, regardless of plant growth stage at time of application. Since imazethapyr and imazamox are chemically similar, the two could not be differentiated based on visual observation of symptoms.

Key symptoms were observed allowing for differentiation between glyphosate and imazethapyr or imazamox at vegetative and reproductive growth stages; however, at the reproductive growth stages, these herbicides expressed similar visual symptoms. The injury symptoms observed on plants treated with glyphosate during vegetative growth were a general chlorosis in the uppermost leaves to plant death. If the plant survives the herbicide treatment the newest leaf to emerge following treatment often emerged tightly rolled. 

The injury symptoms observed with imazethapyr or imazamox on plants treated during vegetative growth were interveinal chlorosis in the uppermost leaves to plant death. Leaves of treated plants often exhibited small, narrow reddish-brown leaf lesions similar to those associated with leaf blast disease of rice. Subsequent tillers on recovering treated plants often emerged along a single plane resulting in a flat, fan-shaped appearance in plants.

Visual symptomology observed on plants treated with glyphosate and imazethapyr or imazamox at reproductive growth stages were various forms of foliar and inflorescence malformations. Foliar symptoms were plants having multiple shoots arising from the secondary nodes of the main stem. The flag leaf on the main stem and secondary shoots would often appear wrinkled, contorted, or rolled. In some instances secondary shoots were stunted or both stunted and malformed. At maturity some panicles failed to fully exert beyond the flag leaf sheath or emerged from the side of the sheath. Often with imazethapyr or imazamox panicles failed to initiate emersion from the flag leaf sheath and decomposed in the leaf sheath causing necrosis of the flag leaf if the plants were treated at the boot growth stage. Individual florets malformations that were observed were florets that were void of a developing grain with only a bleached lemma and palea remaining with glyphosate, and individual florets with tips of the lemma excessively curved toward the palea with glyphosate and imazethapyr or imazamox causing an appearance often referred to as “parrot-beaked” when observed in association with the straighthead physiological disorder of rice.

Foliar symptoms observed on rice plants treated with glufosinate begin as small reddish-brown lesions within 2 days after treatment (DAT) becoming irregularly shaped chlorotic lesions within 7 DAT on affected leaves. By 14 DAT, new leaf growth had initiated in plants with chlorotic lesions increasing in size on the lower leaves ultimately resulting in necrosis of the leaf. By 28 DAT, visual symptoms were often undetectable, compared with nontreated plants.

Based on the symptomology observed in these studies a LSU AgCenter Extension publication was developed to assist growers, consultants, and extension personnel with identification of a herbicide drift event occurring to rice.




INVASIVE PLANT ECOLOGY AND MANAGEMENT. S. L. Young*; University of Nebraska-Lincoln, North Platte, NE (73)

ABSTRACT

Invasive plant species can establish in diverse environments and with the increase in human mobility, they are no longer restricted to isolated pockets in remote parts of the world. Cheat grass (Bromus tectorum L.) in rangelands, purple loosestrife (Lythrum salicaria L.) in wet lands and Canada thistle (Cirsium arvense (L.) Scop.) in wild lands are examples of the most common invasive plant species that are plaguing many regions in the US by creating dense monocultures over many thousands of hectares. Across the world, invasive plant species like water hyacinth (Eichhornia crassipes (Mart.) Solms), cogon grass (Imperata cylindrica (L.) Beauv.), and mile-a-minute (Mikania micrantha Kunth) have choked waterways, altered fire regimes or caused the abandonment of farmland due to their dominating and persistent presence.

 

Clearly, the effects of invasive plant species have reached global scales and their related costs have been estimated in the billions of dollars. The question that has not adequately been addressed is whether landowners and managers are making significant progress in managing invasive plant species populations. Control techniques are widely available and include biological, chemical, cultural, and mechanical, yet invasive plant species continue to threaten many ecosystems on local and regional scales, particularly rangelands, wild lands, and grasslands.

 

One way to indirectly address the rapid advancement of invasive plant species is through awareness and education. Opportunities are needed to provide land owners and managers with the basic principles and practices related to invasive plant ecology and management. In addition, policy makers and the public need to be made aware of the seriousness of invasive plant species. Several short courses that focus on or include invasive plant species have been developed recently and could play a major role in educating individuals with broad backgrounds and experiences.

 

This poster will summarize these courses and speculate on their far-reaching effects. The most successful programs have started with awareness and then education. Maybe it is time to take a page out of one of the most successful public service announcements from the US Forest Service, which reminds us that "only you can prevent forest fires”.




EFFICACY OF A LOW VOLUME, LOW PRESSURE GLYPHOSATE APPLICATION COMPARED TO A TRADITIONAL APPLICATION. G. R. Kruger*1, R. N. Klein1, J. A. Golus1, T. J. Dorr1, J. A. Eastin2; 1University of Nebraska-Lincoln, North Platte, NE, 2Kamterter Products, LLC., Lincoln, NE (74)

ABSTRACT

Most glyphosate applications are made using 7 to 20 gallons per acre using between 20 and 60 psi. However, if a sprayer system can deliver similar efficacy at lower spray volumes, the water and time savings that would result could change the way we look at making spray applications. An efficacy study was conducted using a factorial arrangement of treatments which included four rates of glyphosate and two different sprayer systems. In this study, a traditional sprayer was used to deliver glyphosate at 10 GPA and 40 psi and a no liquid flow pressure sprayer with a 1 to 2 psi air pressured atomizer at 2 GPA. Glyphosate was applied at 4, 8, 16 and 32 oz/acre with each of the two sprayer systems. Applications were made to 15 ft. wide and 45 ft. long plots. Control of kochia and volunteer wheat were recorded at 2 and 4 WAT. Visual estimations of control did not differ between the two spray systems.



ADJUVANT CERTIFICATION THROUGH THE CHEMICAL PRODUCERS AND DISTRIBUTORS ASSOCIATION. M. L. Bernards1, G. K. Dahl*2; 1University of Nebraska-Lincoln, Lincoln, NE, 2Winfield Solutions, LLC, Minneapolis, MN (75)

ABSTRACT

The Chemical Producers and Distributors Association (CPDA) has instituted a certification program for adjuvants. This program was developed to address issues including adjuvants not being registered like pesticides, customer confusion and frustration from lack of standardized definitions, undefined functionality claims, safety and handling concerns, inconsistent composition, variable performance and use of incorrect products or rates. The adjuvant certification program is voluntary. The applicant submits an application, including the company address, contact information, product name, product type, product label, toxicity studies, and the MSDS. CPDA reviews the application information for accuracy, completeness, and compliance with CPDA labeling and performance standards. After the review is completed and certification fees are paid the product is designated as a “CPDA Certified Adjuvant”. The CPDA Certified Adjuvant program has improved understanding of adjuvants.  CPDA developed and adopted “Labeling and Performance Standards for Spray Adjuvants and Soil Conditioners”. Adjuvant terminology has been standardized using terminology and in ASTM Designation E 609 and E 1519. The CPDA Certified Adjuvant Program is is gaining recognition in the industry and now includes several dozen products.




ALTERNATING TEMPERATURE ALTERS THE TRANSCRIPTOME OF LEAFY SPURGE SEEDS AFTER PRETREATMENT AT CONSTANT TEMPERATURE. M. E. Foley*, W. S. Chao; USDA-ARS, Fargo, ND (76)

ABSTRACT

Seeds of the noxious perennial weed leafy spurge (Euphorbia esula) did not germinate when imbibed at a constant temperature of 20°C for 21 d, but transfer of these seeds to an alternating 20:30°C (16:8 h) temperature induced germination. No germination was observed in 21 d imbibed seeds after exposure to alternating temperatures for 1 d, but exposure to alternating temperatures for 3 d resulted in 20% germination. Final germination rates of 65% were observed after imbibed seeds were exposed to 21 d of alternating temperature. In this study, alternating temperature was essential for germination. Changes in seed transcriptomes were compared under four conditions: A) seeds incubated for 21 d at 20°C (imbibed but germination incompetent); B) 21 d imbibed and 1 d at 20:30°C (pre-germination); C) 21 d imbibed but not germinated after 3 d at 20:30°C; and D) 21 d imbibed but germinated between 2 and 21 d at 20:30°C. Using seeds imbibed for 21 d at constant 20°C (A) as a baseline, transcriptome analysis revealed that 597, 1491, and 1329 genes were differentially-expressed (P<0.05) when compared with pre-germinating seeds after 1 d at 20:30°C (A vs. B); non-germinated seeds after 3 d at 20:30°C (A vs. C); and germinated seeds between 2 and 21 d at 20:30°C (A vs. D), respectively. Functional classifications based on gene ontology and subnetwork analyses were performed to identify genes related to the aforementioned treatments. Subnetwork analysis identified key genes involved in glucose, sucrose, abscisic acid, and auxin signaling soon after transferring imbibed seeds (21 d at 20°C) to alternating conditions (1 d at 20:30°C). Further incubation under alternating conditions identified genes involved in oxygen, gibberellin, glucose, ethylene, and light signaling.



RESPONSE OF NEBRASKA KOCHIA (KOCHIA SCOPARIA) POPULATIONS TO DICAMBA. R. J. Crespo*1, M. L. Bernards1, G. R. Kruger2, R. G. Wilson3, D. J. Lee1; 1University of Nebraska-Lincoln, Lincoln, NE, 2University of Nebraska-Lincoln, North Platte, NE, 3University of Nebraska, Scottsbluff, NE (77)

ABSTRACT

Kochia [Kochia scoparia (L.) Roth] is a problematic weed in field crops, rangeland, and waste areas in semiarid regions of the Great Plains and western United States and Canada. Biotypes of kochia have evolved resistance to several herbicide modes of action, including ALS-inhibitors, PSII-inhibitors, synthetic auxins and glycines. Soybean genetically modified to resist dicamba is being developed to provide a new mode of action to help manage some glyphosate-resistant weeds. A risk assessment that estimates the potential for key weeds to develop resistance to new technologies should be made prior to commercialization and should serve as the basis of stewardship programs to protect the sustainability of that technology. The objective of this study was to measure the response of eleven kochia populations to dicamba dose. Kochia populations were collected in southeast Nebraska in 2009. Experiments were conducted in greenhouses at the University of Nebraska-Lincoln. Kochia seed was planted in potting media in 0.9 l plastic pots. When plants reached 10 cm in height they were treated with one of eleven doses of dicamba (0, 17, 35, 68, 105, 140, 420, 560, 1,120, 2,240 and 4,480 g ae ha-1) applied in a chamber sprayer equipped with a TP8001E nozzle. The carrier rate was 193 L ha-1 and the spray pressure was 207 KPa. Visual ratings were taken 7, 14, 21 and 28 days after treatment (DAT). Plants were harvested 28 DAT, dried and dry weights were recorded. The percent dry weight reduction was calculated relative to the control treatment. Data from the 28 DAT visual ratings and percent dry weight reduction were fit to a four parameter log-logistic model for each population. The most susceptible and most tolerant populations differed depending upon the metric used. When the ED90 was calculated for the percent dry weight reduction data, population 53 was 6.3 fold more tolerant to dicamba than population 80. The ED90 of population 53 was 7422 g ha-1 and the ED90 of population 80 was 1179 g ha-1. When the ED90 was calculated for the 28 DAT visual control ratings population 91 was 3.5 fold more tolerant than population 73. The ED90 of population 91 was 4979 g ha-1, and of population 73 was 1441 g ha-1. The common use rate of 280 g dicamba ha-1 would not achieving 90% control in any of the populations evaluated. Two replications of populations 45 and 73 were not harvested for dry matter and were observed for an additional 3 months. All plants treated with a rate of 1120 g ha-1 or less survived and set seeds.




DOES THE DORMANCY OF WEED SEEDS BREAK BY THE PASSAGE THROUGH DIGESTIVE TRACT IN HOLSTEIN CATTLE? S. Rahimi1, H. Rahimian Mashhadi*2, M. D. Banadaki1; 1University of Tehran, Karaj, Iran, 2University of Tehran, Tehran, Iran (78)

ABSTRACT

Does the dormancy of weed seeds break by the passage through digestive tract in Holstein cattle?

Salman Rahimi*, Hamid R. Mashhadi, and Mehdi D. Banadaky

* Department of Agronomy and Plant Breeding, and Department of Animal Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

Dormancy is a trait that has been acquired during evolution by selection for the ability to survive in adverse environments. An understanding of dormancy fluctuations when seeds are exposed to different biological factors is of ecological importance. Study was carried out to test the effect of digestive tract of four Holstein cattle groups(Lactating cows, Feedlot male calves, Dry cows and Growing heifers) on change in germination rates of four weed species (Cuscuta campestris Yuncker., Polygonum aviculare L. and Sorghum halepense (L.) Pers(hight dormancy), and Rumex crispus L.(non-dormant)). One thousand five hundred seeds of each species were fed per each Kg of the their dry matter intake. Germination of seeds recovered 1, 2, 3, and 4 days after seed intake were determined. Befor seed intake, seed germination rates of C.campestris, P.aviculare, S.halepense, and R.crispus were 3%, 0%, 87%, and 3%, respectively. When averaged over all excretion intervals, dry cows significantly reduced germination of R.crispus compared to other cattle groups. P.aviculare seed germination rate was not affected by passage through the digestive tract of all cattle groups. Germination rates of C.campestris and S.halepense were maximum in the recovered seeds in the third day after seed intake in all cattle groups. These values were 10% and 10.5% for S.halepense and C.campestris in lactating cows and feedlot male claves, respectively. S.halepense and C.campestris seeds recovered from lactating cows and feedlot male claves had significantly higher germination rates compared to their rates befor seed intake.

*Corresponding author’s E-mail: s.rahimi@live.com

 

 

 

 

 

 

 

 

 

 

 

 

 

Baskin, J. M. and C. C. Baskin. 2006. A classification system for seed dormancy. Seed. Sci. Res. 14:1-16

Batlla, D. and R. L. Benech-Arnold. 2004. Cahnges in the light sensitivity of buried Polygonum aviculare seeds in relation to cold-induced dormancy loss: development of a predictive model. New Phytologist. 165: 445-452.

Bradford, K. J. and H. Nonogaki. 2007. Seed development, dormancy and germination. Annual Plant Review :Books, Vol 27.

Gardner, C. J., J. G. McIvor. and A. Jansen. 1993. Passage of legume and grass seeds through the digestive tract of cattle and their survival in faeces. J. Appl. Ecol. 30: 63–74.

Harmon, G.W. and F.D. Keim. 1934. The percentage and viability of weed seeds recovered in the feces of farm animals and their longevity when buried in manure. J. Amer. Soc. Agron. 26: 762-767.

Illius, A. W. and I. J. Gordon. 1991.Prediction of intake and digestion in ruminants by a model of rumen kinetics: integration animal size and plant characteristics. J. Agri. Sci. 116:145-157.

Jones, R. M. and Simao Neto, M. 1987. Recovery of pasture seed ingested by ruminants 3. The effects of the amount of seed in the diet and of diet quality on seed recovery from sheep. Aus. J. Exp. Agri. 27(2): 253 – 256

Kelly, K. M., J. Van Staden. and W. E. Bell. 1992. Seed coat structure and dormancy. Plant Growth Regulation. 11:201-209.

Kennedy, P. M. and M. R. Murphy. 1988. The nutrional implications of differential passage of particles through the ruminant alimentary tract. Nut. Res. Rev. 1:189-208

Ocumpaugh, W. R., C. R. Tischler. and L. S. Valle. 1995. Post-harvest seed dormancy effects on Kleingrass germination following simulated digestion by cattle. Crop Sci. 32:260-263.

Van Klinken. R. D. and L. Flack. 2005. Wet heat as a mechanism for dormancy release and germination of seeds with physical dormancy. Weed Sci. 53:663-669.

Whitacre, M. K. and C. A. Call. 2006.Recovery and germinability of native seed fed to cattle. Western North American Naturalist. 66(1): 121-128.




PREFERENTIAL PREDATION OF COOL-SEASON GRASS SEED BY THE COMMON CRICKET (ACHETA DOMESTICUS). R. D. Williams*1, P. W. Bartholomew2; 1USDA-ARS, Oklahoma City, OK, 2USDA-ARS, Langston, OK (79)

ABSTRACT

In field experiments we noted that one of the main predators of tall fescue (Festuca arundinacea Schreb.)  and Italian ryegrass (Lolium multiflorum Lam.) seed was the field cricket (Gryllus sp.).  To determine if there might be a seed predation preference among forage grasses a laboratory study was conducted using the common cricket (Acheta domesticus L.).  Six cool-season grasses were selected and feeding studies were conducted over a three day period. The study was designed as a randomized complete block and repeated in time to provide six replications.  Overall average consumption cool-season grass seed was 77%.  Among the cool-season grasses timothy (Phleum pratense L.), Kentucky bluegrass, and orchard grass (Dactylis glomerata L.) had the greatest predation (96 to 100%).  Predation was related to seed size with the smaller seeds being consumed in greater numbers than the larger seeds.  One could hypothesizes is that the greater consumption of the smaller seed was due to more seed being required to provide the same caloric intake of a fewer larger seed.  To see if there might be selective predation a series of feeding trials were preformed where the crickets were provide with single grass seed or a combination of  two different grass seeds.  Preliminary results indicate that there was no difference between tall fescue and Italian ryegrass predation when seed were provided separately.  However, when seeds of both grasses were offered there was a preference for the tall fescue seed as expressed in more seed being consumed.    This preference did not appear to be due to seed size.  When Italian ryegrass was pared with orchard grass, a much smaller seed, the predation smaller orchard grass seed was much greater than that of the ryegrass.  Other preferences among the other species examined will provided.



MICROSCOPIC CHARACTERIZATION OF RUBBER PARTICLES IN PRICKLY LETTUCE (LACTUCA SERRIOLA). J. L. Bell*, I. C. Burke, M. M. Neff; Washington State University, Pullman, WA (80)

ABSTRACT

Prickly lettuce contains high molecular weight polyisoprene and has potential as an alternative source of natural rubber. Rubber producing plants synthesize and store polyisoprene in sub-cellular rubber particles. To further characterize prickly lettuce rubber producing capabilities, rubber particles were isolated and measured by scanning electron microscopy. Latex from greenhouse grown plants was collected into ice cold buffer containing 100mM Tris-HCl, 5mM MgSO4, and 5mM DTT in de-ionized water at pH 7.5. Latex was centrifuged to pellet particles, and supernatant was decanted. Particles were washed three times then stored in buffer at 4°C as washed rubber particles (WRPs). WRPs were initially fixed with 3% glutaraldehyde in 50mM sodium cacodylate and 1% tannic acid at room temperature for 1 h. Fixed particles were washed three times in 50mM sodium cacodylate then post fixed in 1% osmium tetroxide (OsO4) for 18hrs. Fixed particles were washed and stored in distilled water. Suspended particles were placed on a cover glass mounted on a stub and allowed to air dry. Samples were gold coated before viewing by Field Emission Scanning Electron Microscopy (FESEM). Most of the observed WRPs had an average diameter of 0.288 µm (SE ±0.005) and ranged in size from 0.88 µm to 0.443 µm. Fewer, larger particles were also observed ranging from 0.575 µm to 4.9 µm. Prickly lettuce particles have a similar size range as Brazilian rubber tree (Hevea brasiliensis).




ANALYZING CROP, SOIL, AND TERRAIN IMPACTS ON WEED SEED BANKS USING RANDOM FORESTS REGRESSION. R. Unger*1, D. R. Huggins1, I. C. Burke1, E. Gallandt2, S. Higgins1; 1Washington State University, Pullman, WA, 2University of Maine, Orono, ME (81)

ABSTRACT

Managing the weed seed bank is key to reducing weed seed accumulation and overall weed populations. Understanding how crop rotation, soil characteristics, and terrain influence the weed seed bank may help identify field-related factors that contribute to greater weed pressure. A multi-year cropping systems study in a no-till regime with six different three year rotations of spring wheat (SW) – winter wheat (WW) – alternative crop rotation (winter or spring plantings of barley, canola, or pea) was initiated in 2001 on the Washington State University Cook Agronomy Farm near Pullman, WA. One objective for this study was to better understand how conservation tillage and crop rotation practices affect weed species composition and distribution across the landscape. Each of the six rotations was represented by a farm-scale plot. A baseline for the weed seed bank was established in 1999 by taking soil cores from 369 1 m2 quadrats. In 2007 the soil seed bank was sampled at 369 georeferenced points by taking two 10.16 cm soil samples down to 12.7 cm. The cores were germinated for eight weeks before being homogenized in 8 cm2 plastic trays and germinated for an additional eight weeks. This was done to ensure exhaustive germination of the samples. Samples were watered regularly. Weed germination was recorded by species on one week intervals over the course of the study. Every four weeks the samples were re-randomized on the greenhouse benches. Initially, nonmetric multidimensional scaling (NMS) ordinations using PC-ORD software (version 5.0) were conducted to examine compositional differences in the weed seed bank community among rotations over the two sampling intervals. Due to low weed abundance, only two-thirds of the field site was analyzed using NMS. Over the area analyzed, wild oat (Avena fatua L.) and common lambsquarters (Chenopodium album L.) abundance decreased while Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] and mayweed chamomile (Anthemis cotula L.) increased when the rotation was WW - SW - spring alternative crop rotation. Weed species composition in winter canola or barley alternative crop systems changed from wild oat and common lambsquarters to prickly lettuce (Lactuca serriola L.), while weed species composition in winter pea changed depending on field position, becoming dominated by Italian ryegrass or prickly lettuce. The data were then analyzed using Random Forest Regression to attempt to address the entire field. Between 15.87% and 22.2% of the variation in the appearance of Italian ryegrass was explained by the crop rotation, soil, or terrain. Elevation was the largest contributing factor, but global irradiation, flow direction, flow accumulation, and specific catchment area also influenced Italian ryegrass populations. Terrain, environmental, and soil attributes were not contributing factors for the distribution of the remainder of the weed species, confirming the results of the NMS ordinations. The observed changes in weed species composition agree with the changes that have occurred in management practices on the site, particularly the repeated use of herbicides for wild oat control.




SEED DEVELOPMENT ON WEEDS CONTROLLED PRIOR TO MATURITY. E. C. Taylor*, C. L. Sprague, K. A. Renner; Michigan State University, East Lansing, MI (82)

ABSTRACT

Seed production by escaped weeds is a concern in both conventional and organic farming systems. Each plant that goes uncontrolled can produce hundreds to thousands of seeds that will emerge over several growing seasons. Weed control measures, such as hand hoeing, mowing, and herbicide applications aim to control these weeds before seed maturity is reached; however, sometimes weed control measures fail. Information is currently lacking on the appropriate time of late season weed removal to prevent the after-ripening of weed seeds (i.e. immature seed matures on the drying plant) and inputs to the seed bank. To determine the reproductive growth stage at which summer annual weeds can be terminated and still produce viable seed we conducted a two year field experiment in East Lansing, MI at the Michigan State University Agronomy Farm. Common lambsquarters, velvetleaf, and giant foxtail plants were collected from soybean fields at three phenological growth stages 1) first appearance of open flowers, 2) formation of immature (green/white) seed, and 3) first appearance of mature seed. Whole plants were collected either by pulling (root attached) or cutting at the base (no root). Once collected, plants were placed in residue bags and the bags placed between rows in a soybean field. Residue bags were recollected in November of each year and the number of mature and immature/damaged seeds recovered from the bags recorded. Plants cut or pulled at the flowering stage did not produce mature seed. However, when plants with immature seed were cut or pulled, all three weed species produced some mature seed, suggesting that seed continued to develop on the weeds left to die in the field.




ENDOPHYTE STATUS OF TALL FESCUE (LOLIUM ARUNDINACEUM) AFFECTS SEED PREDATION. P. W. Bartholomew1, R. D. Williams*2; 1USDA-ARS, Langston, OK, 2USDA-ARS, Oklahoma City, OK (83)

ABSTRACT

In a preliminary study seed of a tall fescue (Festuca arundinacea Schreb.) variety ‘Jesup’ without endophyte were consumed at a slightly higher rate by common cricket (Acheta domesticus L.) in a standard feeding trial than the same fescue variety with the endophyte.  Although, the preference for the endophyte-free tall fescue was consistent among studies, there was no statistical difference between the Jesup free and the Jesup infected seed.  To examine this question further we obtained seed of four tall fescue varieties: two varieties that were infected with endophyte and two varieties that were endophyte free.  Using these varieties it was demonstrated that the endophyte free varieties consistently had higher, statistical different predation (78% and 42 % consumption over a 48-h period) as compared to the endophyte infected varieties (23% and 18% consumption over a 48-h period).  These results combined with earlier results for the Jesup tall fescues indicate that the endophyte infected seed are avoided by crickets when feeding.  The possibility that the presence of the endophyte provides seed with predator avoidance will be discussed.




EFFECTS OF VEGETATIVE COVER AND FOOD LOAD ON WEED SEED PREDATION IN THE UPPER MIDWEST. G. G. Gramig*; North Dakota State University, Fargo, ND (84)

ABSTRACT

Recently, evolution of herbicide resistance and increasing concerns about economic, social, and environmental costs associated with herbicides have led to renewed interest in managing weeds via cultural practices, even in conventionally managed (non-organic) cropping systems. These trends in agricultural production have spurred research to evaluate ecologically based methods of regulating weed population dynamics. Survival of newly dispersed weed seed is the most important phase of the plant’s life cycle for determining future population size. Invertebrate and vertebrate animals remove and destroy large quantities of dispersed weed seed. Understanding and manipulating these natural processes could therefore provide an important tactic for integrated weed management approaches. To explore the potential impact of weed seed predation in the Upper Midwest, field experiments were installed on September 30th, 2009 and September 16th, 2010 at the Central Research Extension Center in Carrington, ND. The objective of these experiments was to develop methodology for future experiments and to estimate the effect of vegetative cover type (wheat stubble vs. organic mixed-species cover crop) on weed seed removal rates via invertebrate and vertebrate seed predators. Petri dishes containing 25 yellow foxtail (Setaria glauca L.) seeds pressed into finely sieved field soil were installed at 12 seed feeding stations spatially arranged in a grid in a field of spring wheat stubble and an adjacent field containing a species-diverse organic cover crop mix. Two Petri dishes were placed at each station: one accessible to all animals and one accessible only to invertebrate animals. Insect pitfall traps were also installed at each feeding station. Game cameras were installed at a subset of feeding stations to digitally “trap” vertebrate predators for identification. During the study period, Petri dishes of seeds were recovered and replaced with full dishes approximately weekly. Prior to installation of the experiment, ¼ m sq quadrats were placed near each feeding station and standing vegetation was removed to determine vegetative cover biomass. During 2010 only, these quadrats were carefully swept to sample crop and weed seeds lying on the soil surface. These samples provided an estimate of the ambient food load in each field. Preliminary results indicated that the removal rate for seeds accessible only to invertebrates was less than the removal rate for seeds accessible to all animals, across years and field types. Vegetative cover biomass did not differ between study years or field types. In 2010, the cover crop field contained much greater weed seed mass on the soil surface compared to the wheat stubble field. However, total seed mass (weed + wheat) did not differ between field types. Pooled across field types and seed dish access types, seed removal rates were much greater in 2010 than in 2009. These differences were most likely due to the weather; in 2009 the study period was unusually cold and wet whereas in 2010 the study period was unusually warm and dry. In 2009, overall seed removal rates were slightly greater in the wheat stubble field than in the cover crop field. Conversely, in 2010, this pattern was reversed. Two factors may have caused these contradictory results. In 2009, the cover crop species mix contained hairy vetch, which created a tangled mat of vegetation near the soil surface which possibly interfered with animal movement. Also, though data is unfortunately lacking to test this idea, the cover crop in 2010 appeared to be more heavily infested with weeds than in 2009. Thus, in 2010, the cover crop field may have had a greater ambient seed load than in 2009, thereby supporting larger numbers of predators and leading to greater seed removal rates than were measured in the wheat stubble field.




INHERITANCE OF EPSPS GENE AMPLIFICATION IN PALMER AMARANTH. D. A. Giacomini*1, S. Ward1, T. A. Gaines2, P. Westra1; 1Colorado State University, Fort Collins, CO, 2University of Western Australia, Crawley, WA, Australia (85)

ABSTRACT

The evolution and inheritance of glyphosate resistance in Palmer amaranth (Amaranthus palmeri) is a major concern for farmers and weed managers.  Previous research has shown resistance to be due to an increased copy number of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene through gene amplification, but the stability of this resistance trait is not yet known.  The relative EPSPS copy numbers of F1 offspring were determined by running quantitative PCR (qPCR) reactions on F1 hybrid plants produced from crosses between resistant and susceptible Palmer amaranth.  The twenty crosses included susceptible by resistant, resistant by susceptible, and resistant by resistant, creating twenty F1 populations.  At least ten plants from each of these F1 populations were sampled and tested with qPCR.  Preliminary data have shown a wide spread of copy numbers for the majority of F1 populations (in the general range of 1-80 EPSPS copies), indicating an unstable transmission of copy number, though no F1 copy numbers have exceeded the copy number of the most resistant parent.  One population had very low copy number in all but one individual, suggesting the influence of either apomixis or maternal effects.  However, subsequent genotyping of the F1s and parents of this population ruled out apomixis as a cause of similar copy numbers.  Initial results have also shown a strong correlation between high copy number and level of resistance, as was expected.  More research on the EPSPS gene is needed to confirm these results and to gain an idea about how glyphosate resistance transmission occurs across generations at the molecular level.  It may be that a genetic mobile element with low stability may be partially responsible for the increased EPSPS copy numbers in Palmer amaranth.




PERSISTENCE AND SURVIVAL OF HOARY ALYSSUM (BERTEROA INCANA (L.) DC). G. J. Stopps, M. K. Upadhyaya*; University of British Columbia, Vancouver, BC (86)

ABSTRACT

Hoary alyssum (Berteroa incana (L.) DC) is a serious weed of pastures and rangelands in British Columbia, Canada. Knowledge of vulnerable links in the persistence strategy of this weed is necessary for its effective cultural management. We studied the size and distribution of hoary alyssum soil seed banks, its seed dormancy and germination dynamics, allelopathic potential, and the response of this weed to mowing and nitrogen (urea) fertilization. Distribution of seeds in the soil seed bank was studied by taking soil cores, seed dormancy and germination dynamics by establishing artificial soil seed banks as well as Petri dish assays, alleopathic influence of water-soluble leaf leachates on seed germination and seedling elongation of associated forage grasses using Petri dish and in-soil bioassays, and effects of timing of mowing and nitrogen fertilization in greenhouse pot-culture experiments. The results showed that 94% of hoary alyssum seeds were confined to the top 4 cm of the soil profile, the size of its soil seed banks ranged between 0 to 132.4 million seeds/ha, seeds did not exhibit long-term primary dormancy but buried seeds in artificial seed banks showed some enforced as well as induced dormancy. Hoary alyssum leaf leachate strongly inhibited seed germination of a variety of grassy species in Petri dish assays and species differed in this regard. This inhibition was however not consistently observed in in-soil experiments. Hoary alyssum shoot biomass as well as bolting increased with increasing rate of nitrogen fertilization in pot culture studies. Mowing of flowering shoots resulted in production of new shoots due to release of apical dominance. Mowed plants produced nearly the same number of shoots per rosette as that present prior to mowing. Delay of mowing following bolting increased plant mortality and decreased fecundity by limiting the time available for seed production by the regenerated shoots. However this enhanced mortality cannot be exploited to control this weed because the delay required may allow the weed to produce a significant number of seeds prior to mowing.




WEED SEEDBANK DYNAMICS IN FOUR CONTRASTING ORGANIC FEED AND FORAGE PRODUCTION SYSTEMS. R. G. Smith*1, D. A. Mortensen2, M. E. Barbercheck2, D. J. Sandy2; 1University of New Hampshire, Durham, NH, 2The Pennsylvania State University, University Park, PA (87)

ABSTRACT

An improved systems-level understanding of how different approaches to weed and soil quality management affect weed population and community dynamics is necessary to develop effective weed management practices in organic production systems.  We assessed the density, composition and diversity of the readily germinable fraction of the soil weed seed bank in the spring and fall each year (2007-2010) following organic certification in four replicated feed and forage production systems in central PA.  The four systems differed in the intensity of tillage during the three-year transition period prior to organic certification (full or minimum-till), weed population densities at the end of the transition period (low densities in full-till; high densities in minimum-till), and the subsequent approach to weed and soil management implemented during the three years following organic certification.  Following organic certification, germinable weed seed bank densities increased more than four-fold by the final year of the study in system 1 (high initial weed densities due to minimum tillage during the transition period, and tilled only in the first of the three years following organic certification).  In contrast, seed bank densities and species richness in the final year of the study were lowest in the system that employed the most intense tillage practices over the first two years post-certification (system 3), despite this system also having high initial weed densities due to minimum tillage during the transition period.  Relative to the effect of the four management systems, the timing of seed bank sampling (spring versus fall) was a strong determinant of weed seed bank community composition.  Smartweed (Polygonum spp.) and wild buckwheat (Polygonum convolvulus L.) were strongly associated with the spring seed bank, while purslane speedwell (Veronica peregrina L.) and field pennycress (Thlaspi arvense L.) were the most consistent indicators of the fall seed bank.  Results from this study suggest that rotating minimum tillage practices (for soil quality improvement) with tillage-intensive practices (aimed at reducing weed populations) may be a viable approach to managing the readily germinable fraction of the weed seed bank.  However, more work will be necessary to determine the optimal balance between full and minimum tillage phases over an organic rotation and how initial seed bank density and composition may dictate the periods of time within each phase (full or minimum tillage) required to realize desired goals for weed management and soil quality over the longer-term.



WEED EMERGENCE AND GROWTH IN STRIP-TILLED SYSTEMS: SEPARATING THE EFFECTS OF TILLAGE, COVER CROPS, AND CROP COMPETITION. E. Haramoto*, D. C. Brainard; Michigan State University, East Lansing, MI (88)

ABSTRACT

Strip tilled (ST) fields, particularly those with a cover crop, are heterogeneous environments—in-row (IR) areas have a crop, tilled soil, and incorporated cover crop residue, while the between-row (BR) areas have no crop, no tillage, and a cover crop surface mulch.  Learning more about how weeds respond to these different environments will provide information that farmers can use to better manage weeds by manipulating tillage and cover cropping.   We hypothesized that ST systems would have lower weed emergence (due to the lack of tillage-induced germination stimuli) and growth (because of lower nitrogen content), with enhanced effects with a cover crop.  A fully factorial field experiment was designed to separate the effects of three different factors on weed emergence and growth.  The factors were tillage (ST or chisel plow followed by field cultivation (CT)), cover crop (spring-planted oat (Avena sativa L.) or none), and crop competition (cabbage or no cabbage).  To measure weed emergence, quadrats of Powell amaranth (Amaranthus powellii S. Wats.) and common lambsquarters (Chenopodium album L.) seeds were established in both IR and BR locations immediately following tillage and again nine days later following cabbage planting; emerged seedlings were counted and pulled daily.  To assess individual weed growth, Powell amaranth seedlings were transplanted in and between each crop row (or in the corresponding location when no crop was present) and sampled both at mid-season and at cabbage maturity.  Post-tillage, there were 68% fewer Powell amaranth seedlings emerging BR in ST plots compared to CT plots, regardless of whether a cover crop was present.  Post-planting, in plots without cabbage, both BR and IR Powell amaranth emergence in ST plots was higher with oat residue compared to no cover crop; in cover cropped plots, emergence was higher in ST compared to CT.  Common lambsquarters emergence was similar in all treatments at both times.  In the growth portion of this experiment, mid-season Powell amaranth biomass was 75% lower BR and 25% lower IR when cabbage was present, but neither tillage nor cover crop significantly affected mid-season growth.  In contrast, final Powell amaranth biomass was often influenced by tillage, with results varying based on crop and location.  In-row, when cabbage was present, tillage did not affect Powell amaranth biomass.  However, when cabbage was not present, IR Powell amaranth plants grown in ST plots were 50% smaller than those grown in CT plots.  Between-row, the opposite trends were observed: when cabbage was present, BR weeds were 50% larger in ST compared to CT.  Total final cabbage biomass (plants and heads) at harvest was not affected by treatment.  In the absence of cabbage, tillage had no effect on BR weeds.  These results suggest that there are complex interactions between these factors and that their impacts on weed emergence and growth may not always be as expected. 




DEVELOPING A HYDROTHERMAL MODEL TO PREDICT EMERGENCE OF ANNUAL WEED SPECIES IN IOWA. R. Werle*1, L. D. Sandell1, M. L. Bernards1, J. L. Lindquist1, D. D. Buhler2, R. G. Hartzler3; 1University of Nebraska-Lincoln, Lincoln, NE, 2U.S. Department of Agriculture / Agricultural Research Service, Ames, IA, 3Iowa State University, Ames, IA (89)

ABSTRACT

Seed banks in agricultural lands contain many weed species.  Knowledge of when these species are likely to emerge is important in planning effective weed control programs. Hydrothermal time models have been used to predict weed emergence based upon soil temperature and water potential in relation to base temperature and soil water potential thresholds. Field experiments were conducted between 1996 and 1999 at Iowa State University`s Johnson Farm (41.98º N, 93.64º W) in Story County, Iowa, to develop empirical models based on hydrothermal time to predict emergence of four summer annual weed species in Iowa.  The soil was a Clarion loam with 4.6% organic matter and a pH of 6.7. A randomized complete block design with four species (common lambsquarters, green foxtail, redroot pigweed and velvetleaf), two initiation dates (1996 and 1997) and three replicates was used. Each experimental unit contained 1000 seeds of a single species. An experimental unit was composed of a 20 by 20 by 15 cm deep plastic crate in 1996 and 30 cm diameter by 15 cm deep polyvinylchloride cylinders (PVC) in 1997. In November of 1996 and 1997, seeds were buried by removing the upper 5 cm of soil within a frame, placing it in a bucket, adding the seeds of an individual species, mixing the seeds with the soil, and then returning the soil to the frame and packing it by hand. Seedling emergence counts started on April 1, 1997 and April 3, 1998 for the first and second initiation dates, respectively, and were conducted weekly for a two year period within each initiation date to evaluate first and second year seed bank emergence. Emerged plants were counted and removed weekly until no additional emergence was observed in each year. Daily maximum and minimum air temperature were measured at 1.5 m height during the growing season with an in situ sensor connected to a data logger and precipitation data were obtained from a weather station within 2.2 km of the experimental site. Daily soil water potential and temperature at 2 cm deep was estimated using the STM2 software based upon the daily maximum and minimum air temperature, precipitation and soil characteristics. Emergence data were converted from weekly counts to a cumulative fraction emergence based on the total plants that emerged each year. The values for Tbase and Ψbase for each species were based on the published literature. The models were created by regressing the two year cumulative fraction emergence from the first initiation date (1996) of each species against the calculated cumulative hydrothermal time using the Weibull function. The models were validated using the first (1998) and second (1999) year cumulative fraction emergence from the second initiation date (1997). Root-mean-square error values comparing observed and predicted cumulative fraction emergence were calculated to estimate model accuracy, and ranged from 8.60 to 20.80% for common lambsquarters, 11.76 to 13.92% for green foxtail, 19.50 to 19.95% for redroot pigweed, and 10.23 to 21.96% for velvetleaf.




GROWTH AND DEVELOPMENT OF ARTEMESIA ANNUA IN EASTERN WASHINGTON. H. C. Malone*, I. C. Burke, B. Pan; Washington State University, Pullman, WA (90)

ABSTRACT

Artemisia annua L. (sweet wormwood), a member of the Asteraceae family, produces the antimalarial sesquiterpene lactone endoperoxide, artemisinin. Artemisinin (ART) is effective for the malaria causing parasite, Plasmodium spp., some cancers, and against other human and animal parasite diseases such as Coccidia spp., Babesia spp., and Leishmania spp. Malaria has developed a resistance to most drugs currently used, making ART one of the last known modes of treatment and leading to high worldwide demand. ART has been recommended by the World Health Organization as a component of artemisisin-combination therapy (ACT) for malaria. However, to date, artemisinin cannot be produced in large amounts synthetically due to its complex structure, requiring extraction from A. annua. As yields of ART are very low (0.01%-0.80%), development of new cultivars and understanding the biosynthesis and conditions influencing artemisisin yield are essential. A recently funded project to assess ART for cancer therapy included an effort to assess and potentially develop an ART production industry alongside the mint and hop industry in eastern Washington. Therefore, the objective of the study was to examine the growth and development of A. annua in eastern Washington to identify production practices that will maximize biomass accumulation and ART yield. An open-pollinated biotype of A . annua was transplanted on three dates, May 10, June 10, and June 16, 2010, at Central Ferry, WA. Planting density was 1 m between plants within rows and 2.4 m between rows. The plants were irrigated with underground drip lines. From July to October, weekly height, above ground biomass, and ART concentration was measured. At anthesis, plants transplanted on May 10 had a mean height 142 cm (+/- 2.1) and dry biomass was 674 g (+/- 49.2). When transplanted on June 6, the mean height at anthesis was 143 cm (+/- 1.7) and dry biomass was 820 g (+/- 79.1). When transplanted on June 6, the mean height at anthesis was less than the previous planting dates, 117 cm (+/- 2.4), and dry biomass was also lower, at 357 g (+/- 28.5). At anthesis 572 g ha-1 (+/- 103.9) of ART can be harvested. ART yield from the earliest planting date was 1029 g ha-1(+/- 135.5), and the latest 2 planting dates were 488 g ha-1 (+/- 102).Planting early in the season resulted in the largest accumulation of biomass and height, and as a consequence, achieved the highest ART yield, when compared to the last planting date.




THE SIGNIFICANCE OF SORGHUM EXUDATES ON THE GERMINATION OF THE PARASITIC WEED, STRIGA HERMONTHICA. L. C. Andresen*1, J. C. Streibig1, B. W. Strobel2, A. M. Rimando3, T. H. Nielsen1, V. Leth1; 1University of Copenhagen, Taastrup, Denmark, 2Univesity of Copenhagen, Frederiksberg, Denmark, 3USDA-ARS, Oxford, MS (91)

ABSTRACT

Striga spp. (Witchweed) is considered the largest biological constraint on crop production in sub-Saharan Africa. The subterranean life of the parasitic weed Striga hermonthica is complex, and the chemical interaction between Striga seed germination and Sorghum is subject for our study.

Root hairs of the host Sorghum (Sorghum bicolor) deposit compounds into the rhizosphere, which stimulate germination of Striga seeds at low concentrations. Bioassay evaluation of these compounds may eventually lead to identification of varieties of Sorghum that are stimulant or inhibitory of Striga germination. We have developed a simple 12-well plate bioassay that allows direct application of samples on Striga seeds: Seeds are exposed to root extract, TLC fractions of the root extracts or pure compounds, and germination is recorded after 48 hours. Our ultimate goal is to isolate and test the effect of isolated compounds on Striga hermonthica seed germination using this assay.

In the current study, we tested 15 varieties of Sorghum landraces. Stimulant activity was observed with TLC fractions of the root extracts of ‘dobbs’, ‘SX 17’, and ‘brown streibig’. The fractions were located below sorgoleone on the TLC plate. This is confirmatory of a previous study1, where the TLC fraction below sorgoleone distinguished between susceptible and resistant Sorghum varieties. Our results further confirm that the compound that stimulates germination of Striga hermonthica seeds is not sorgoleone but a compound that has a longer retention time on the silica gel TLC plate developed with 35% hexane in propanol. We are currently pursuing identification of the stimulatory compound(s) and further aim to use these as chemical marker to screen Sorghum varieties.

 

Louise C. Andresen: loand@life.ku.dk and landrese@olemiss.edu

 

I) European Weed Research Society “Parasitic Weeds” Working Group Inauguration Meeting; cost action 849.  23-24 November 2006. Instituto de Tecnologia Quimica e Biologica Oeiras, Lisabon, Portugal.

 




EFFECT OF STORAGE CONDITIONS AND CORN COMPETITION ON SEED GERMINATION OF JIMSONWEED AND COCKLEBUR. F. Kordbacheh*1, H. Rahimian Mashhadi2, H. Alizadeh1, R. Tavakol Afshari1; 1Tehran University, Karaj, Iran, 2University of Tehran, Tehran, Iran (92)

ABSTRACT

Effect of storage conditions and corn competition on seed germination of jimsonweed (Datura stramonium) and cocklebur (Xanthium strumarium). Farnaz Kordbacheh, Hamid Rahimian-Mashhadi, Hassan Alizadeh, Reza Tavakol-Afshari. University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

The ambient condition to which the parent plant is subjected may influence the subsequent germinablity of seeds. Seeds may experience different microenvironments depending on the crowdness of neighbors, therefore, may show variation in germination response to such environments. This hypothesis was examined by conducting field and laboratory experiments on jimsonweed (Datura stramonium) and cocklebur (Xanthium strumarium) in 2007. Both weed species were planted in pure stand and in competition with corn at densities of 4,8,12 and 16 plants m-2. Light intensities and the R/FR ratios were measured in each treatment. Seeds from both weed species were collected in each plot. All seeds were kept at room temperature, and also buried in soil at 10 and 20cm depths for six months. Jimsonweed seeds had high initial germination
(75%) after harvesting. In freshly harvested seeds of jimsonweed, germination of weed seeds increased with increasing jimsonweed density in both monoculture and in competition with corn treatments. This can be explained by R/FR ratios and light intensity data within the canopy in different treatments. While, in cocklebur, germination decreased with increasing density in both monoculture and competition with corn. As expected in lower densities, higher R/FR ratio and higher light transmission was observed under the canopy. There was no significant difference between inter-specific competition treatments in jimsonweed seed germination kept under different conditions for six months; however, jimsonweed seed germination significantly decreased under intra-specific competition with increasing densities. An increase in germination of cocklebur seeds kept in different conditions for six months was observed, with increasing cocklebur density. During six months under room temperature conditions the peak of jimsonweed seed germination occurred 45 days after being kept at this condition and then significantly declined to day of 180. In cocklebur, no seed germination was observed during six months under room temperature conditions except day 45th, when a germination of 5% was recorded. Under both soil depths, germination of jimsonweed increased with time and peaked at 90 days after burial. Tetrazolium chloride test indicated that jimsonweed seed dormancy was 75% and 55% in 10 and 20cm soil depths at beginning of the burial treatments respectively; However, seeds buried under 10 and 20cm soil depths for six months showed 22.5% and 18.0% germination respectively. Fnz_kordbacheh@yahoo.com.

 Bello, I. A., M. D. Owen, and H. M. Hatterman-Valenti. 1995. Effects of shade on velvetleaf (Abutilon theophrasti) growth, seed production, and dormancy. Weed Technol. 9:452-455.

Braniard, D. C, R. R. Bellinder, and A. DiTommaso. 2005. Effect of canopy shade on the morphology, phenology, and seed characteristics of powell amaranth (Amaranthus powellii). Weed Sci. 53:175-186.

Fenner, M. 1985. Seed ecology. Chapman and Hall, London, UK.

Gill, N. 1938. The variability of weed seeds at various stage of maturity. Ann. Appl. Biol. 25:447-456.

Holm. L., J. Doll, E. M. Holm J. Pancho, and J. Herberger. 1997. World weeds: Natural histories and distribution. John Wiley & Sons, Inc.
Nurse, R. E., and A. DiTommaso. 2005. Corn competition alters the germinablity of velvetleaf (Abutilon theophrasti) seeds. Weed Sci. 53:479-488.
Norsworthy, J. 2004. Soybean canopy formation effects on pitted morningglory (Ipomoea lacunosa), common cocklebur (Xanthium strumarium), and sicklepod (Senna obtusifolia) emergence. Weed Sci. 52:954-960..




EFFECTS OF SOIL WATER LEVEL ON DORMANCY, GERMINATION AND MORTALITY OF WEED SEED. T. Imaizumi*, M. Asai, H. Watanabe, A. Uchino; National Agricultural Research Center, Tsukuba, Japan (93)

ABSTRACT

The effects of soil water levels on seed dormancy and viability of soybean weed species were evaluated. Experiments were conducted on seeds of barnyardgrass (Echinochloa crus-galli var. crus-galli), devil's beggartick (Bidens frondosa), southern crabgrass (Digitaria ciliaris), ladysthumb (Polygonum persicaria), curlytop knotweed (P. lapathifolia), common lambsquarters (Chenopodium album), divine nightshade (Solanum nigrescens), slender amaranthus (Amaranthus viridis), smooth pigweed (A. hybridus), livid amaranthus (A. blitum), Powell's amaranthus (A. powellii) and redroot pigweed (A. retroflexus). In February 2010, the seeds were placed on the soil surface or buried at a depth of 7.5 cm in pots of 25 cm diameter ×30 cm depth. The pots were subjected to different soil water level treatments: moist (the groundwater level of the pots was 10 cm below the soil surface), submerged (the pots were kept submerged with 7.5 cm of water) and control (upland condition pots) treatments. The seeds were retrieved from the pots in April, May, June and July 2010, and dormancy and viability were determined by germination and tetrazolium tests. The soil water level treatments reduced viability of seed retrieved from the soil surface more than retrieved from the 10 cm depth. Seed of several weed species retrieved from the soil surface were less viable in the submerged and/or moist treatments than in the control treatment. Viability of seed retrieved from the 10 cm depth were same among the treatments, except for common lambsquaters. The effects of soil water levels on dormancy were not detected, except for common lambsquaters seed retrieved from the 10 cm depth. Dormancy of the common lambsquaters seed in the submerged treatment was deeper than in the moist and control treatments.



DISTRIBUTION OF GLYPHOSATE-RESISTANT AND -SUSCEPTIBLE HAIRY FLEABANE (CONYZA BONARIENSIS) AND THEIR PHENOLOGY IN CENTRAL CALIFORNIA. A. Shrestha*1, B. D. Hanson2, M. L. Moretti1; 1California State University, Fresno, CA, 2University of California, Davis, Davis, CA (94)

ABSTRACT

Hairy fleabane (Conyza bonariensis) is a common weed in orchards and vineyards of Central California.  In 2007, the presence of a glyphosate-resistant (GR) biotype of hairy fleabane was documented at a site in Central California.  While another GR Conyza species, horseweed (Conyza canadensis), was found to be widely spread throughout the region, the distribution of GR hairy fleabane is unknown.  A previous study also found differences in the phenological development of GR and glyphosate-susceptible (GS) horseweed.  The GR horseweed developed more rapidly and produced seeds almost a month earlier than the GS horseweed. However, it is not known if such differences exist in the case of GR and GS hairy fleabane.  Therefore, the objective of this research was to determine the distribution of GR hairy fleabane and to determine the phenology of the GR and GS hairy fleabane.  Preliminary results indicate that, similar to horseweed, GR hairy fleabane is also fairly widespread in Central California.  Phenology of GR and GS hairy fleabane collected from 10 locations in Central California is being monitored and a degree day model for these biotypes is being developed. 




ELUCIDATING THE INHERITANCE OF EVOLVED RESISTANCE TO GLYPHOSATE IN POPULATIONS OF PALMER AMARANTH (AMARANTHUS PALMERI) FROM NORTH CAROLINA. A. Chandi*1, S. Mila-Lewis1, D. L. Jordan1, J. D. Burton1, A. York1, J. Whitaker2, A. S. Culpepper3; 1North Carolina State University, Raleigh, NC, 2University of Georgia, Statesboro, GA, 3University of Georgia, Tifton, GA (95)

ABSTRACT

ELUCIDATING THE INHERITANCE OF EVOLVED RESISTANCE TO GLYPHOSATE IN POPULATIONS OF PALMER AMARANTH (Amaranthus palmeri S. Wats.) FROM NORTH CAROLINA. A. Chandi *£, S. Milla-Lewis£, D. L. Jordan£, J. D. Burton£, A. York£, J. Whitaker¥, A.S. Culpepper¥

ABSTRACT

Glyphosate is world’s most widely used herbicide. Being non-selective, it is used to control wide array of weed species including both grasses and broad leaf weeds. Many populations of Palmer amaranth have developed resistance to glyphosate in recent years because of repeated applications of this herbicide. Although appearance of glyphosate resistant Palmer amaranth biotypes has been documented very well but not enough information is available about the mode of inheritance of resistance. Research was conducted to study inheritance of glyphosate resistance in a Palmer amaranth population from North Carolina. Plants from a glyphosate resistant (R) and a susceptible population (S) were used to make reciprocal crosses and generated 16 F1 families (RxS and SxR eight of each kind). A dose response study was carried out on F1 families along with R and S parents. Selected surviving males from each of the F1 families were back crossed with S females to form 16 BC1F1 families. I50 values for R, S, RxS and SxR were 1735, 51, 1388, and 1159, respectively. Dose response behavior of F1 progeny showed lower resistance when compared with R parent population indicating that resistance was not fully dominant over susceptibility. Lack of significant difference between reciprocal F1 families suggested that genetic control of glyphosate resistance is governed by nuclear genome and there is no maternal or cytoplasmic inheritance involved. Further, segregation of the resistance trait in backcross families is currently being analyzed to determine if it is consistent with single gene mechanism of inheritance.

£ North Carolina State University Raleigh

 ¥ University of Georgia, Tifton




PARAMETERIZATION OF THE BARNYARDGRASS RESISTANCE SIMULATION MODEL FOR RICE. M. V. Bagavathiannan*1, J. K. Norsworthy1, K. L. Smith2, P. Neve3; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Monticello, Monticello, AR, 3University of Warwick, Wellesbourne, England (96)

ABSTRACT

Parameterization of the barnyardgrass (Echinochloa crus-galli) resistance simulation model for rice. Muthukumar V. Bagavathiannan*, Jason K. Norsworthy, University of Arkansas, Fayetteville, AR; Kenneth L. Smith, University of Arkansas, Monticello, Monticello, AR; and Paul Neve, University of Warwick, Wellesbourne, United Kingdom.

Barnyardgrass is the most important weed of Arkansas rice, and currently, herbicide-resistant barnyardgrass (resistant to propanil and quinclorac) is widespread in rice production systems in this region.  In addition, barnyardgrass biotypes resistant to imazethapyr have been documented in Arkansas rice. Extensive use of chemicals with insufficient rotation has aided the evolution of multiple resistant barnyardgrass populations. A mathematical model is being developed to simulate the simultaneous evolution of barnyardgrass resistance to acetyl-CoA carboxylase- and acetolactate synthase-inhibiting herbicides in rice. The model is being used i) to understand the risks of evolution of resistance under current management practices, and ii) to identify proactive strategies that will help slow the evolution of resistance. The modeling framework consists of three integral components: biology, genetics, and management. The emergence pattern of barnyardgrass observed in Arkansas was used to assign emerging seedlings into different cohorts according to the timing of management operations. Efficacies were defined for each management option for each cohort. The model represented a 60-ha rice field with a background barnyardgrass seedbank of 2000 viable seeds m-2. For each run, the initial frequency of resistant alleles was varied between 5e-8 and 1e-7. The initial composition of different biotypes (SS, Rr, and rr) were calculated based on Hardy-Weinberg equilibrium. The outputs for 250 model runs for a 30-year period were summarized and analyzed. Resistance is considered to have evolved if the proportion of resistant seeds is >20% of the total seedbank. The poster contains more details on model parameterization. At this stage, the model does not account for new mutations, seed immigration, and crop rotation.  Future efforts will continue to refine the model and test different scenarios in order to understand the influence of management strategies on the evolution of resistance. muthu@uark.edu




IS THE BIOFUEL SWITCHGRASS AN INVASION RISK IN CALIFORNIA? J. N. Barney*1, J. M. DiTomaso2; 1Virginia Tech, Blacksburg, VA, 2University of California, Davis, Davis, CA (97)

ABSTRACT

To meet mandated energy demands for liquid transportation fuels and biomass-based electricity, dedicated energy crops will soon be planted on millions of hectares of US land. Switchgrass (Panicum virgatum L.), non-native to the western US, is a leading contender as a biomass crop due to its high yields, broad adaptability, and tolerance of poor growing conditions-traits that typify many of our worst invasive species. We have conducted a series of experiments to evaluate the probability of switchgrass escaping the cultivated environment and becoming an invasive species in California. The standard Weed Risk Assessment suggests that switchgrass has a high invasive potential in California unless a sterile cultivar is used-suggesting that the invasive potential lies in seed production and dispersal. A greenhouse study demonstrated that switchgrass is tolerant of both very dry (-11 MPa) and flooded soils, which increases the environments switchgrass can survive in moisture-limited California. However, a modeling study shows that riparian areas are the habitats of most concern as dryland areas are too dry for switchgrass, though we have demonstrated that roots can reach nearly 3m deep in the establishment year. An ongoing field experiment is evaluating the survival and establishment potential of switchgrass using a controlled introduction in a local stream. Survival is low in upland (rain-fed) conditions with or without competition from resident vegetation. Survival and establishment is much higher in lowland conditions with most individuals growing large and flowering. Switchgrass appears to be a minor threat in dryland California due to limited soil moisture availability. However, riparian areas may serve as propagule reservoirs as switchgrass is capable of germinating, surviving, and establishing when water is not limiting. If sterile cultivars are introduced for biofuel production the invasive potential of switchgrass appears very low. 




INTRA- AND INTER-SPECIFIC INTERFERENCE BETWEEN RICE AND HERBICIDE-RESISTANT AND -SUSCEPTIBLE ECHINOCHLOA PHYLLOPOGON. L. G. Boddy*1, M. S. Bhullar2, J. C. Streibig3, A. J. Fischer1; 1University of California, Davis, Davis, CA, 2Punjab Agricultural University, Ludhiana, India, 3Royal Veterinary and Agricultural University, Thovarldsenvej, Denmark (98)

ABSTRACT

Late watergrass (LWG) is an important weed of paddy rice in temperate regions, and in California has evolved resistance to most available herbicides. We studied the ecological fitness of herbicide-resistant (R) and –susceptible (S) LWG biotypes, as well as the nature of interference between these biotypes and rice, using both an additive design and a response surface approach combined with treatments to isolate root and shoot interference. Inter-specific interference on rice from both R and S biotypes was 8 and 11 times more intense than intra-specific interference between rice plants, respectively. Although R biotypes were shorter, had less leaf area and above-ground biomass than S biotypes, strong below-ground interactions enabled R plants to be equally suppressive of rice growth as S plants. R plants deployed a greater proportion of their root biomass (0.63 ±0.02 vs. 0.56 ±0.02 for S) in the upper 3.5 cm of soil, which is where most rice roots were placed. Analysis of relative yield totals (RYT ≥ 1) did not detect antagonistic interactions, and since pots were water saturated, we infer that interference was due mostly to competition for soil nutrients. In spite of similar interference abilities between R and S plants and between both biotypes and rice, a comparison of two R and two S biotypes found that R plants exhibited a significant fitness disadvantage by producing a 48-73% lower seed output than S plants. However, a separate comparison of six biotypes found that R plants shattered their mature seed 23-31 days before S plants, which should enable better seed bank replenishment through partial escape of seed removal by harvest operations. Therefore, since R plants are equally damaging of rice yields as S plants, they will require similar levels of weed control; however, their reproductive fitness disadvantage provides opportunities for management if early shattering can be prevented.



APPLYING THE CONCEPT OF HYDROTHERMAL TIME TO MODEL DORMANCY AND GERMINATION IN ECHINOCHLOA PHYLLOPOGON. L. G. Boddy*, K. J. Bradford, A. J. Fischer; University of California, Davis, Davis, CA (99)

ABSTRACT

Rice in California is seeded and grown under flooded conditions, mostly to control weeds. Yields are threatened by the emergence and spread of herbicide resistant (R) late watergrass (LWG), an aquatic rice mimic that has evolved multiple resistance to virtually all available selective grass herbicides. Among the limited number of control alternatives, the most promising is the stale seedbed method of recruiting weeds and removing them with a broad spectrum herbicide for which resistance has not yet evolved. Since the planting season is limited, the effectiveness of this method hinges on the ability to accurately forecast weed emergence patterns, which depend on the dual processes of dormancy and germination. Seed stratification levels are a major determinant of germination rates and percentages, and responses differ between R and herbicide–susceptible (S) seed. We used population based threshold models to describe and predict dormancy and germination patterns for R and S LWG; in particular we adapted the hydrothermal model, previously developed to predict germination, to predict dormancy release across a range of stratification temperatures and moisture levels.




GROWTH AND DEVELOPMENT AMONG PRICKLY NIGHTSHADES FROM SOUTHEASTERN UNITED STATES. C. T. Bryson*1, K. N. Reddy1, J. D. Byrd2; 1USDA-ARS, Stoneville, MS, 2Mississippi State University, Mississippi State, MS (100)

ABSTRACT

Native and non-native prickly nightshades (Solanum) are troublesome weeds of pastures, feed lots, right-of-ways, croplands, and natural areas.  In agricultural settings, many prickly nightshades interfere with crop growth, quality, and harvest efficiency.  Research was conducted in greenhouse studies at Stoneville, MS, to determine the comparative growth and development among 11 native and non-native species of prickly nightshades found in the southeastern United States:  buffalobur (Solanum rostratum Dun.); horsenettle (S. carolinense L.); Jamaican nightshgade [S. jamaicense P. Mill.]; nipplefruit nightshade (S. mammosum L.); red soda apple (S. capsicoides All.); silverleaf nightshade (S. eleaegnifolium Cav.); sticky nightshade (S. sisymbriifolium Lam.); tropical soda apple (S. viarum Dun.); turkeyberry (S. torvum Sw.); western horsenettle (S.dimidiatum Raf.); and wetland nightshade (S. tampicense Dun.).  Plants were established from seed in 26-cm diam plastic pots filled with potting media and soil and maintained in the greenhouse at 30/22 C (± 3 C) day/night temperature.  Plant heights and number of leaves were recorded weekly.  Plants were harvested at 10 wk after emergence (WAE) and dry weights recorded.  The experiment was repeated.  At 10 WAE emergence, average plant height was 24 cm for horsenettle, 26 cm for Jamaican nightshgade, 47 cm for turkeyberry, and western horsenettle, 57 cm for tropical soda apple, 62 cm for red soda apple, 85cm for nipplefruit nightshade, 97 cm for  buffalobur and silverleaf nightshade, 100 cm wetland nightshade, and 105 cm for sticky nightshade, respectively. By 10 WAE, the average number of leaves per plant ranged from < 10 for horsenettle and turkeyberry to > 40 leaves per plant for buffalobur and western nightshade.  Average dry weights were greatest for buffalobur, nipplefruit nightshade, and red soda apple (>17 g) and least for horsenettle (1 g).  Based on these data, nightshade growth rates and dry weight were variable among species and these rates may be a result of reproductive phenology, annual or perennial. charles.bryson@ars.usda.gov




KOCHIA WITH ALS (AHAS) MUTATIONS: MORE ON THE MANITOBA CONUNDRUM. A. Legere*1, H. G. Beckie1, B. Hrynewich1, C. Lozinski1, E. N. Johnson2, S. Warwick3, C. Stevenson4; 1Agriculture and Agri-Food Canada, Saskatoon, SK, 2Agriculture and Agri-Food Canada, Scott, SK, 3Agriculture and Agri-Food Canada, Ottawa, ON, 4Private Consultant, Saskatoon, SK (101)

ABSTRACT

Growth of kochia (Kochia scoparia L.) biotypes from Manitoba, Saskatchewan and Alberta resistant to acetolactate synthase (ALS/AHAS) inhibitor herbicides (HR) with mutations at either Pro197-Gln or Trp574-Leu was compared to herbicide susceptible (HS) biotypes under greenhouse conditions. Growth of Manitoba (MB) accessions differed from that of Saskatchewan and Alberta accessions, with MB HS plants growing poorly compared to MB HR plants, regardless of mutation, and to HS plants from other provinces. The Manitoba HR and HS biotypes were grown again in the greenhouse to confirm inter/intra-population differences. MB kochia plant architecture and biomass allocation varied with population and biotype. Results were more consistent across experiments when HS biotypes were compared with HR biotypes with the Trp574-Leu than with the Pro 197-Gln mutation. Trp574-Leu HR plants produced more shoot and root biomass than HS plants, whereas Pro 197-Gln HR plants produced more root biomass than HS plants in the first experiment only. In the first experiment, HS plants reached the flowering stage (BBCH 60) earlier than HR plants and consequently produced more seed biomass than HR plants in spite of less shoot and root biomass. In an attempt to explain the unique growth pattern of the MB HS biotype, kochia accessions were checked for resistance to other modes of action (groups 4, 5, 9), but none was found. To this day, we have no explanation for the poor growth and different architecture of MB HS plants compared to other HS and HR kochia populations from the Canadian prairies.



SPURRED ANODA, TALL MORNINGGLORY, AND WRIGHT’S GROUNDCHERRY ARE NOT AFFECTED BY MELOIDOGYNE INCOGNITA AND VERTICILLIUM DAHLIA CO-INFECTION. J. Schroeder*1, C. Fiore1, S. Thomas1, J. Trojan1, S. Sanogo1, L. Liess1, N. Schmidt1, L. Murray2; 1New Mexico State University, Las Cruces, NM, 2Kansas State University, Manhattan, KS (102)

ABSTRACT

In 2007 the three predominant annual weed species encountered in chile pepper (Capsicum annuum) fields in Luna County, NM were all found to be infected with Verticillium dahliae (= VERT). These weeds included spurred anoda (Anoda cristata), Wright’s groundcherry (Physalis wrightii) and tall morningglory (Ipomoea purpurea), none of which expressed symptoms of Verticillium wilt that were prevalent in surrounding chile plants.  All three weeds are also known hosts of southern root-knot nematode (M. incognita, = Mi), with symptoms of nematode infection being evident on roots of tall morningglory and chile in some of the affected fields.  The limited expression of symptoms of VERT infection among weeds led us to hypothesize that, in addition to their competitive impact on chile, weeds may serve as refugia that maintain or enhance populations of certain pathogens that can be injurious to chile.  Greenhouse experiments were conducted during the summers of 2008 and 2009 to determine the effects of Mi and VERT, alone and in combination, on growth of spurred anoda, Wright’s groundcherry, tall morningglory, and chile compared to non-inoculated control plants.  Meloidogyne incognita reproduction determined by egg production, V. dahliae infection confirmed by culturing stem sections and roots, and plant shoot and root growth proportional to that of non-inoculated control plants were measured six weeks post-inoculation.  Shoot, root, and total biomass of the three weed species was not affected by the pathogens, alone or combined, in 2008 or 2009 experiments.  However, in 2008, total root and shoot biomass of chile was reduced 48% and 74% by VERT or the combination of VERT and Mi, respectively.  In 2009, chile biomass was reduced 69% by VERT only. Overall, Mi reproduction levels were similar among chile, tall morningglory and Wright’s groundcherry in both studies.  Reproduction factors (nematode populations 45 days post-inoculation divided by inoculum level) ranged from 60 to 83 in 2008, but declined to less than one tenth of that level in 2009, possibly due to differences in plant size at time of inoculation.  Spurred anoda was a poorer host for Mi than the other species in both experiments.  Co-infection with VERT had little effect on nematode reproduction in these experiments. These results demonstrate that all three weeds will support both pathogens, alone or in combination, without suffering pathogenic effects, and that tall morningglory and Wright’s groundcherry support levels of M. incognita reproduction similar to those found in highly-susceptible chile plants.  Effective management of these weeds may help reduce populations of both pathogens in future crops.




THE EFFECT OF LIMITED IRRIGATION ON WEED EMERGENCE AND SEED PRODUCTION IN CORN AND SUNFLOWER. L. Wiles*1, D. Remucal2, W. Bausch3, T. Trout3, D. L. Shaner2; 1USDA-ARS, Fort Collins, CO, 2USDA, Fort Collins, CO, 3USDA-ARS, Water Management Research Unit, Fort Collins, CO (103)

ABSTRACT

Deficit irrigation (DI) is a potential strategy to sustain irrigated crop production in the Great Plains in the face of increased competition between urban and agricultural uses of declining water supplies.  Less water is supplied than is needed to meet the full evapotranspiration demand of the crop and the timing of irrigation may also be changed so water stress occurs when it will have the least impact on crop yield. Changing the amount and timing of irrigation will influence weed establishment and population growth and could potentially lead to weed shifts. We studied emergence and seed production of selected weeds in a DI corn experiment as the first step in predicting weed problems with DI.  Seedlings of lambsquarters (Chenopodium album L.), pigweed (Amaranthus retroflexus L.), barnyardgrass (Echinochloa crus-galli (L.) Beauv. ), toothed spurge (Euphorbia dentata Michx.) and Venice mallow (Hibiscus trionum L.) were counted in the crop row approximately every ten days in 2009 and 2010, and biomass and seed production of toothed spurge and lambsquarters, grown between rows, were measured in 2010. Irrigation treatments were full irrigation, 70% of full irrigation at each application, and 70% and 55% of full irrigation with applications staged to stress the crop more during vegetative than reproductive growth. The irrigation scheduling resulted in DI of 81, 68 and 51% (2009) and 82, 72 and 61% (2010) of full irrigation during weed emergence. The amount and pattern of emergence was not affected by DI in 2009 because irrigation was not needed until after most weeds emerged. In 2010, DI reduced emergence of all species, except Venice mallow.  The period of emergence was longer for barnyardgrass with 61% compared to 100% irrigation, but shorter for the other species. Lambsquarters produced the most seeds with the least irrigation. Crop canopy in this treatment peaked at 70% ground cover compared 93% cover with full irrigation. Predicting weed problems with DI requires understanding the influence of the amount and timing of the deficit directly (less water) and indirectly (reduced crop canopy) on weed population dynamics.  




EFFECT OF SAFLUFENACIL ON GLYPHOSATE-RESISTANT AND -SUSCEPTIBLE HORSEWEED (CONYZA CANADENSIS) BIOTYPES. A. Shrestha*, M. L. Moretti; California State University, Fresno, CA (104)

ABSTRACT

Horseweed (Conyza canadensis) is a common weed in orchards and vineyards in the San Joaquin Valley (SJV) of California.  Glyphosate has been an herbicide of choice for postemergence control of horseweed in these perennial cropping systems.  However, with the discovery of a glyphosate-resistant (GR) biotype of horseweed in many locations of the SJV, growers are actively seeking for alternative controls.  Saflufenacil (Treevix®) is being registered by BASF for postemergence weed control in orchards in California. However, the effect of saflufenacil on GR horseweed is unknown. A greenhouse study was conducted to study the effect of saflufenacil-alone at 70 g ha-1 or with glyphosate (Roundup Weathermax) at various combination rates (70, 140, 280, 560 g ha-1 of saflufenacil + glyphosate 0.87, 1.73, 3.47, or 6.94 kg ae ha-1) on a previously confirmed population of GR and a glyphosate-susceptible (GS) horseweed.  A glyphosate-alone (0.87 kg ae ha-1) was also included. Applications were made with a flat fan 8002 XR nozzle at a volume of 182 l ha-1 at the 5- to 8-leaf and at the rosette stage of horseweed.  None of the GR or the GS horseweed survived any of the rates of saflufenacil either alone or in combination with glyphosate at any of the growth stages.  However, the GR plants survived the glyphosate alone treatment. Therefore, saflufenacil alone has the potential to control GR horseweed in the orchards of SJV but broad-spectrum weed control may be obtained if it is tank-mixed with glyphosate.   




FACTORS AFFECTING GERMINATION OF SPANISHNEEDLES (BIDENS BIPINNATA L.). A. M. Ramirez*, M. -. Singh; University of Florida, Lake Alfred, FL (105)

ABSTRACT

Spanishneedles (Bidens bipinnata L.) is a native annual weed commonly found in many citrus groves in FL. Three laboratory experiments were conducted to determine the effect of seed age, light, and temperature, seed age and depth of burial and osmotic potential of germination medium on the germination of Spanishneedles. The first study was on the effect of seed age, temperature and light. Day/Night temperatures used were 15/10, 20/15, 25/20, 30/25, 35/30, 40/45 and 45/40 °C while light settings were complete exposure to light and no light. Seeds used were from Fellsmere collected in 2007 and Lake Alfred collected in 2010. The second experiment was on the effect of depths of burial and seeds were sown at the surface (0 cm) or at 1, 2, 4, 6, 10 cm. Solutions with osmotic potentials of 0, -0.3, -0.4, -0.6, -0.9 and -1.3 mPa were used for the third experiment. In all experiments twenty five seeds of Spanishneedles were placed in petri dishes lined with filter paper and treatments were arranged in a randomized complete block with four replications. Germination of Spanishneedles was affected by seed age, temperature, light, depth of burial and osmotic potential of the germination solution. Higher germination was observed (>95%) in old seeds grown under dark condition at a temperature range of 20-30°C. Germination increased as temperature increased to 30°C and started to decrease at temperature of 40°C. Zero to minimal germination occurred at 45°C regardless of seed age and light conditions. Germination decreased as depth of burial increased with greatest germination occurring at the surface regardless of seed age. No germination was observed when seeds were buried at 10 cm. Germination decreased as the osmotic potential of the solution increased. ahmramirez@ufl.edu




NOVEL USE OF TRINEXAPAC-ETHYL TO STUDY REQUIREMENT OF GIBBERELLINS FOR SEED DORMANCY BREAKAGE. H. R. Huarte*, M. L. Zapiola; Universidad Católica Argentina, Buenos Aires, Argentina (106)

ABSTRACT

Seed dormancy breakage requires an increment in GAs content and/or sensitivity to GAs. Lower germination of seeds incubated in solutions containing compounds that reduce GAs synthesis provides evidence that GAs is required to break seed dormancy. Trinexapac-ethyl (TE), a GAs synthesis inhibitor, is frequently used as a growth regulator in seed production. However, to the best of our knowledge, TE has not been used to prove involvement of GAs in seed dormancy breakage. We conducted germination studies using dormant seeds of artichoke thistle (Cynara cardunculus L.) and common teasel (Dipsacus fullonun L.) under a range of TE concentrations (0-500 µM TE), and a combined solution of 125µM TE + 100µM GA3 for artichoke thistle and 250µM TE + 100µM GA3 for common teasel. Germination tests were conducted at 20/10C (12 h thermoperiod) in darkness for artichoke thistle and 15C with 12h light for common teasel. Germination of artichoke thistle in 125µM TE was reduced to 42.6 % when compared to the check (98.3 %), but the combined TE + GA3 solution restored germination to 88.1 %. Germination of common teasel in 250µM TE was reduced to 13.3% when compared to the check (96 %) and the combined TE + GA3 solution restored germination to 68.3%. These results provide evidence about the utility of using TE to study the role of GAs in braking seed dormancy. robertohuarte@uca.edu.ar




BREAKING SEED DORMANCY IN COMMON TEASEL. H. R. Huarte, M. L. Zapiola*; Universidad Católica Argentina, Buenos Aires, Argentina (107)

ABSTRACT

Seed dormancy is a characteristic found in many weeds and non-domesticated species. Common teasel (Dipsacus fullonum L.) is a very aggressive, biennial, prolific, exotic species capable of colonizing natural and improved pastures. Populations from USA and Germany were reported to germinate promptly when exposed to seed dormancy release factors, such as fluctuating temperatures and light. The objectives of this study were to determine the effect of light (12h photoperiod and darkness) and temperature (fluctuating 20/10C for 12h, and constant 15C) on breaking seed dormancy of a population collected at Buenos Aires, Argentina, and demonstrate that the response to light and fluctuating temperatures in breaking seed dormancy is mediated by gibberellins (GAs). We included a GA synthesis inhibitor, trinexapac-ethyl (TE), and water incubation treatments. Germination tests were conducted using 30 seeds x 3 replications for each treatment combination. Either light or fluctuating temperatures was enough to induce germination in common teasel. For those incubated in water, there was no difference in germination between the light + 20/10C (95.5%), light + 15C (96.4%), and dark + 20/10C (100%) while the dark + 15 C had lower germination (12.0%). The effect of GAs on inducing germination was confirmed by the blockage of germination by TE regardless of the light and temperature conditions. Also, the exposure of seeds to an increasing concentration of GA3 (0, 50 and 250μM) increased the germination under dark and constant temperatures for the 250μM GA3 treatment (95.6%). Understanding how the environment affects seed dormancy and germination is useful for designing adequate weed management practices. robertohuarte@uca.edu.ar




A GENOMIC APPROACH TO INVESTIGATE THE WEEDINESS OF JOINTED GOATGRASS (AEGILOPS CYLINDRICA). E. Sanchez Olguin*, A. Liston, C. Mallory-Smith; Oregon State University, Corvallis, OR (108)

ABSTRACT

Jointed goatgrass (Aegilops cylindrica Host) is a widespread weedy species that mainly inhabits wheat fields but also is found in dry disturbed sites, fencerows, and roadsides. In wheat production, Ae. cylindrica reduces yield and decreases wheat grain quality. Ae. cylindrica is difficult to control in the field because hexaploid wheat (Triticum aestivum L.; 2n = 6x = 42; AABBDD genomes) and Ae. cylindrica are close relatives and share a progenitor species. Ae. cylindrica is an autogamous, allotetraploid species (2n = 4x = 28; CCDD genomes) of the Triticeae tribe. The diploid species Ae. markgrafii L. (2n = 2x = 14, CC) has been identified as the donor of the C genome and Ae. tauschii (2n = 2x = 14, DD) as the donor of the D genome.  The geographic distribution of Ae. cylindrica extends beyond the areas where the diploid progenitors are found. In addition, neither of the progenitor species is considered an important weed. The weediness of Ae. cylindrica and its ability to adapt and compete in wheat fields could be a gain in plasticity due to the alloploidization or the result of selection in favor of competitive genotypes. A comparison between the C and D genomes of Ae. cylindrica  to the ancestral species can provide signs of selection in Ae. cylindrica genome.  A cDNA library was constructed from leaf tissue from one accession each of Ae. cylindrica, Ae. tauschii and Ae. markgrafii.  Between 6.5 and 7.2 million sequences of 36 base pairs were recovered from the samples and used for the data analysis. The sequences were aligned to a collection of wheat expressed sequence tags (ESTs). The EST collection included 216,196 sequences with a mean length of 700 base pairs. Single point mutations (SNPs) were recorded and compared among the three species. A total of 64,459 SNPs were observed, 74.2% were present only in one species, 10.2% in two species and 15.6% in all three species.  Aegilops cylindrica had the greatest number of SNPs, almost double those of Ae. markgrafii and Ae. tauschii. A total of 3,394 SNPs were present in Ae. cylindrica and Ae. markgrafii but not in Ae. tauschii. In contrast, 1,131 SNPs were present in Ae. cylindrica and Ae. tauschii but not in Ae. markgrafii. The number of SNPs per EST varied from 1 to 30, with a mean of 1.86 and 2.26 SNPs per EST respectively in Ae. margrafii and Ae. tauschii and a mean of 2.57 for Ae. cylindrica.  The greater number of SNPs was observed in genes such as: phosphorylase, two-pore calcium channel, methionine S-methytransferase and a heat shock factor protein. Further analysis of these genes will help to define their role in the adaptive and competitive ability of Ae. cylindrica

 




POTENTIAL ALLELOPATHIC EFFECTS OF RUZI GRASS (BRACHIARIA RUZIZIENSIS) LEAF AND STEM TISSUES ON WEED SPECIES. E. L. Ishii-Iwamoto*1, R. S. Oliveira Jr.1, J. Constantin1, A. A. Silva2, K. A. Kern Cardoso2, F. A. Rios2, M. S. Mito2, M. Foletto2; 1Universidade Estadual de Maringá, Maringá, Brazil, 2University of Maringá, Maringá, Brazil (109)

ABSTRACT

Potential allelopathic effects of ruzi grass (Brachiaria ruziziensis) leaf and stem tissues on weed species.

 

Ishii-Iwamoto, E.L.*,  Oliveira Júnior, R.S.,  Constantin, J.,  Silva, A.A., Rios, F.A, Mito, M.S.,  Foletto, M., Rocha, M., Kern Cardoso, K.A.,

Department of Biochemistry, University of Maringá, 87020900, Maringá, Brazil.

 

The intercropping of corn and soybean with tropical forages under no-tillage in Brazilian agriculture has been demonstrated to benefit the conservation of natural resources. The plant species used to produce the residues can decrease weed incidence through the release of allelopathic compounds. This work aimed to investigate the sensitivity of the selected weeds, poinsettia (Euphorbia heterophylla L.), morningglory (Ipomoea triloba L.) and beggarticks (Bidens pilosa L.), to residues of ruzi grass. The hydroalcoholic extract of ruzi grass leaves and stems was fractioned using solvents in order of increasing polarity, and the effects of the various fractions on germination, seedling growth and some biochemical parameters were examined. In the concentration range of 250 to 2000 ppm, the butanol fraction (BF) was found to have the most pronounced effect on the weeds. The effects of the other fractions were species dependent. The calculated ID50 for BF inhibitory action on primary root growth after 48 hr of treatment was 420 ± 36 ppm (poinsettia) and 370 ± 34 ppm (morningglory). At 500 ppm, the BF reduced the growth of primary roots of beggarticks by 60 % after 120 hr of treatment. The growth of morningglory seedlings was also reduced by the aqueous fraction (AF), whereas the beggarticks was sensitive to the ethyl acetate (EA) and AF. Increased respiratory activity was found in the primary roots of poinsettia and morningglory at 250 ppm BF and higher concentrations. This effect was consistent with an uncoupling action observed in mitochondria isolated from the primary roots of poinsettia. Changes in the activities of antioxidant enzymes, peroxidase (+184%), catalase (+262%), ascorbate peroxidase (+60%) and superoxide dismutase (-37%), were also found in the primary roots of poinsettia. Our experiments reveal that ruzi grass residues can release compounds that are phytotoxic to the assayed weed species. The active compounds may lead to toxicity by interfering with energy metabolism and inducing oxidative stress. High amounts of triterpene saponins and aconitic acid were found in the BF and AF fractions, respectively. Experiments are being conducted to identify other active compounds in these fractions and to determine the effects of pure compounds.   eliiwamoto@uem.br

 Financial support: Fundação Araucária do Estado do Paraná and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

 




RECRUITMENT BIOLOGY AND ECOLOGY OF LARGE [DIGITARIA SANGUINALIS L. (SCOP.)] AND SMALL [DIGITARIA ISCHAEMUM (SCHREB.) EX MUHL.] CRABGRASS IN TURF. F. A. Turner*1, R. Van Acker2; 1University of Guelph, Guelph, ON, 2University of Guelph, Simcoe, ON (110)

ABSTRACT

Large and small crabgrass have proven to be serious weeds in a broad variety of systems; including Canadian row crops, cultivated fields, and turfgrass.  Despite this, minimal research has been conducted on either of these species nation-wide and much of the existing knowledge has been derived from agriculturally focussed investigations.  In turf, crabgrass has previously been managed using herbicides, however, the Ontario-wide cosmetic pesticide ban has restricted their application on lawns, parks, school yards, and cemeteries since April, 2009.  Observation of turfgrass in southern Ontario has confirmed a high incidence of crabgrass in many areas.  As crabgrass has been noted as a dominant weed without the aid of herbicides and, the efficacy of bioherbicides is not yet sufficient, this trend is hypothesized to continue.  Crabgrass biotypes have been proven to exist in other research related to their emergence timing and flowering and may also act to explain some differences seen in separate studies.  Consequently, observational studies of crabgrass emergence timing in southern Ontario turfgrass are being conducted to better characterize crabgrass in this region.  Experimentation of crabgrass’ response to common residential cultural management techniques including fertilization and disturbance by raking is also being investigated.  Previous research has revealed a positive response of both large and small crabgrass seed to treatments of KNO3 by breaking dormancy prematurely and enhancing the rate of germination.  Growth chamber experimentation will reveal direct effects of various fertilization rates on local large and small crabgrass seed, while field experimentation will incorporate the effects of a representative turfgrass ecosystem under fall and spring fertilization, and disturbance treatments.  It is intended that a better understanding of southern Ontario’s existing large and small crabgrass populations in turf, as well as the implications that common cultural management practices have on their recruitment will contribute to their adequate management without the use of herbicides.



BIOLOGICAL CONTROL OF JOHNSONGRASS BY MEANS OF BIPOLARIS SORGHICOLA. H. A. Acciaresi*, G. A. Lampugnani, C. Abramoff, M. C. Stocco, M. S. Zuluaga, C. I. Monaco, N. Mercerat; Fac. Cs. Agrarias y Ftales (UNLP), La Plata, Argentina (111)

ABSTRACT

Johnsongrass is one of the ten most noxious weed in the world, causing great yield losses to crops through competition and allelopathy.

A target leaf spot was found on johnsongrass plants at different growth stages. A severity of 80 % was observed in adult plant.

In most diseased plants, the spots were well defined, delimited by the leaf veins, and elongated. Individual lesions ranged in lengh from small spots (2-3 mm) to large lesions (10-15 mm). Lesions sometimes coalesced to produce extensive areas of necrocis. Isolates identified as Bipolaris sorghicola grew slowly on PDA medium, producing a compact dark brown mycelium. Conidia were 40-80 mm long, slightly curved, golden brown, with three to seven pseudosepta. Although germination of conidia was mainly bipolar, lateral germination was observed in some instances.

Greenhouse inoculations with conidia from monoconidial isolates (105 conidia.cm-3) were used to confirm pathogenicity of B. sorghicola on 4 leaf stage johnsongrass plants. Typical lesions developed after 10 days.  A severity of 25% was observed at 5th unfolded leaf stage. The pathogen was re-isolated from lesions after 15 days. 





BIOCONTROL OF HEMP SESBANIA IN RICE WITH THE FUNGUS COLLETOTRICHUM GLOEOSPORIOIDES F. SP. AESCHYNOMENE FORMULATED IN AN INVERT EMULSION. C. D. Boyette*1, D. R. Gealy2, R. E. Hoagland3, K. C. Vaughn1; 1USDA-ARS, Stoneville, MS, 2USDA-ARS, Stuttgart, AR, 3USDA-ARS, CPSRU, Stoneville, MS (112)

ABSTRACT




WEED SUPPRESSION FROM FALL SEEDED BRASSICA COVER CROPS. D. Anderson, J. B. Masiunas*, J. DeDecker, M. Kushad; University of Illinois, Urbana, IL (113)

ABSTRACT

Alternative cropping systems are needed for reduced pesticide or organic farms. Short cycle cover crops such as fall planted oilseed radish, forage turnip, rapeseed, canola, Ida Gold and Pacific Gold either incorporated in late fall or winter killed may suppress early season weeds in plasticulture systems. We found that black plastic mulch applied immediately after fall incorporation of mustard species retained isothiocynates longer and provided better spring weed surpression than in bare ground systems. Tomato and pumpkin yields were directly related to weed control and were greatest in plastic mulch systems with mustard biomass and tillage between rows.



GLYPHOSATE DRIVEN SELECTION STRIKES AGAIN: INVESTIGATING THE MECHANISM OF RESISTANCE IN ECHINOCHLOA COLONA FROM CALIFORNIA. R. Alarcón-Reverte*, A. García, M. Jasieniuk, T. Lanini, B. D. Hanson, A. J. Fischer; University of California, Davis, Davis, CA (114)

ABSTRACT

Since the appearance of the first glyphosate-resistant weed, Lolium rigidum, in Australia in 1996, resistance to glyphosate has evolved in a total of 21 weed species and is present in 15 countries around the world. Two suspected glyphosate-resistant Echinochloa colona populations, ECHCOL1 and ECHCOL2, were collected in orchard fields of the Northern Sacramento Valley in California and tested for resistance to glyphosate using dose-response experiments and shikimic acid accumulation assays. The dose-response experiments showed that both populations, ECHCOL1 and ECHCOL2, were 6.6 and 4.4 times, respectively, more resistant to glyphosate than the susceptible standard.  The shikimic acid assays showed that the susceptible standard population accumulated 4.6 and 3.2 times more shikimic than ECHCOL1 and ECHCOL2, respectively. The EPSPS gene was amplified and sequenced in all three populations and two different amino acid changes were found in the resistant populations. In the resistant ECHCOL1 population an amino acid change at position 106 from proline to serine was identified, while an amino acid change at the same position from proline to threonine was identified in ECHCOL2. These mutations are potentially responsible for glyphosate resistance in both populations since mutations at this position have been found to confer resistance to glyphosate in other weed species. However, the different resistance levels in each population might indicate that more than one resistance mechanism is involved. Glyphosate translocation and EPSPS gene expression studies are currently being conducted.




CHARACTERIZATION OF GLYPHOSATE RESISTANT SOURGRASS IN BRAZIL. M. S. Melo*1, J. D. Vassios2, M. Nicolai3, S. J. Nissen2, P. J. Christoffoleti3, T. C. Banzato3; 1University of Sao Paulo, Piracicaba, Brazil, 2Colorado State University, Fort Collins, CO, 3Univeristy of Sao Paulo - ESALQ - Brazil, Piracicaba, Brazil (115)

ABSTRACT

Glyphosate resistance is an increasing worldwide issue and has been documented in at least 20 species. In Sao Paulo state, citrus producing areas rely on glyphosate as an important management tool in orchards, as do growers in California’s Central Valley.  This heavy reliance on glyphosate induces a strong selection pressure and increases the potential to select for glyphosate resistant biotypes. Field observations indicate putative resistant sourgrass (Digitaria insularis) biotypes.  Studies were conducted in order to characterize resistance in a biotype collected near Matao, Brazil. Susceptible plants were grown from seed collected in a horticultural area near Piracicaba, Brazil, where no glyphosate had been applied. Three dose-response studies were conducted at different growth stages; the first on seedling plants, the second on tillered plants, and the final on tillered plants that were clipped and allowed to regrow.  Plants were sprayed using an overhead track sprayer with glyphosate treatments ranging from 0 - 11,520 g ae/ha.  In addition to dose-response data, shikimate accumulation in susceptible and resistant biotypes was compared using an in vivo shikimate accumulation assay, with glyphosate rates from 0 – 8,000 mM.  Dose-response results indicate little difference between biotypes when sprayed at the seedling stage, but resistance when sprayed once plants have tillered.  Based on results of all studies, the predicted R:S ratio ranged from 3-4 regardless of plant growth stage; however, LD50 values increased for both biotypes at later growth stages.




GLYPHOSATE RESISTANCE IN SORGHUM HALEPENSE - CONTROL OPTIONS. L. Lorentz*1, A. Hopkins2, R. Beffa3, H. J. Strek4; 1University of Bonn, Frankfurt, Germany, 2Bayer CropScience, Research Triangle Park, NC, 3Bayer CropScience, Frankfurt am Main, Germany, 4Bayer CropScience, Frankfurt, Germany (116)

ABSTRACT

Sorghum halepense or Johnsongrass is an invasive weed species found worldwide and is primarily a problem in warm climates. It was introduced into the US from the Mediterranean region around 1800 as a grain or forage crop. It is a C4 perennial weed species which propagates by seeds or rhizomes. It is listed as one of the ten worst weeds in the US. The first confirmed case of glyphosate resistance was reported in Argentina in 2006 followed by a report in Arkansas in 2007 . Both were found in soybean fields.

We assessed the glyphosate resistance factor and the alternative herbicide options to control this weed. We compared the sensitivity of adult plants (BBCH 43) of several biotypes to glyphosate (EPSPs inhibitor) by assessing the fresh weight under greenhouse conditions. The adult plants were grown from rhizomes and cultivated for 3 months to obtain plants with well-developed rhizomes. Several herbicides with different MoAs were evaluated; tembotrione (HPPD inhibitor), glufosinate (glutamine synthethase inhibitor), nicosulfuron/prosulfuron (ALS inhibitor) and fluazifop-butyl (ACCase inhibitor). The 5-EnolPyruvylShikimat-3-Phosphatesynthase (EPSPs, EC 2.5.1.19) and Acetyl CoA Carboxylase (ACCase, EC 6.4.1.2) genes were checked for known single nucleotide mutations.

As previously described, the adult plants demonstrated a moderate degree of resistance to glyphosate with a resistance factor of 3.6. ALS-inhibitors still show a good level of control of this population despite reported cases of ALS resistance. Glufosinate is known to give generally weaker control of perennial grass species but is still an additional option in fields of row crops together with the LibertyLink® system. The ACCase inhibitor fluazifop-butyl failed completely to control this Arkansas biotype. Our study showed that tembotrione gave good control of this weed in greenhouse conditions.

The known mutation sites in EPSPs and ACCase were analyzed by pyrosequencing. We did not find any alterations in the G101, T102 and P106 mutations sites of EPSPs, thus glyphosate resistance is not based on target-site resistance. The analysis of the ACCase mutation sites 1781, 2027, 2041, 2078 and 2096 showed a mutation in 2027-Cys (GGA to GCA), explaining the poor performance of fluazifop-butyl observed. Our results strongly suggest that the S. halepense biotype found in Arkansas, which has resistance to both glyphosate and aryloxyproprionate ACCase herbicides can alternatively still be controlled by glufosinate and ALS-inhibitors and at least partially by tembotrione. Work to further clarify the glyphosate resistance mechanism is ongoing. (roland.beffa@bayer.com)

 

Acknowledgements

We thank especially JK Norsworthy and RC Scott of the University of Arkansas for sharing their glyphosate resistant plant material and data with us.

 




ASSIMILATE TRANSLOCATION CHANGES CAUSED BY GLYPHOSATE IN LOLIUM PERENNE BIOTYPES OF DIFERENCIAL HERBICIDE SENSITIVITY. M. E. Yanniccari*1, D. Gimenez2, H. A. Acciaresi2, A. M. Castro2; 1Instituto de FisiologĂ­a Vegetal (UNLP-CONICET), La Plata, Argentina, 2Fac. Cs. Agrarias y Ftales (UNLP), La Plata, Argentina (117)

ABSTRACT

Glyphosate is a systemic herbicide that is translocated to shoot and root apexes and underground organs of reserve. However, there are studies that characterize its movement with a "self-limitation" because this herbicide reduces net assimilation of CO2 in source leaves. The objective of the current research was to evaluate the effect of glyphosate on the transport of assimilates, during 6 days post-application of herbicide (DPA), comparing a susceptible and a glyphosate-resistant populations of Lolium perenne.

Plants growing in hydroponics were sprayed with glyphosate (1,080 g ae.ha-1) at tillering. Another set of plants remained as controls without herbicide. At 1, 3, and 6 DPA, the latest expanded leaves on the main tiller were labeled at the down side with glucose (14C (U)). Plants were dissected 24h after labeling and the samples were digested with NaOH (9 N). Finally, the percentage of labeled glucose in each organ was quantified in dpm, using a liquid scintillation counter.

Glucose uptake did not differ significantly between treatments over time in both populations. At 1 DPA, susceptible plants treated with glyphosate retained 53.2% more glucose in the labeled area than their controls reflecting a reduction on the transport. This retention was increased at 3 and 6 DPA. The reduction of assimilates transport did not affect differentially the different sources of the labeled leaf.

By comparing the control plants of both populations, the resistant ones holded more glucose in the labeled area. Otherwise, this biotype did not show differences in the assimilate transference under herbicide treatment compared to their controls, during 6 days DPA. Consequently, glyphosate significantly affected the phloem loading of assimilates in the susceptible population without damage in the resistant one




ABSORPTION AND TRANSLOCATION OF AMINOCYCLOPYRACHLOR IN FOLIAR AND BASAL APPLICATIONS. I. C. Burke*, J. L. Bell, H. C. Malone; Washington State University, Pullman, WA (118)

ABSTRACT

Aminocyclopyrachlor is a new auxin type herbicide proposed to control invasive weeds and brush in nonagricultural areas. To understand herbicide behavior on a woody species absorption and translocation were evaluated on quaking aspen (Populus tremuloides). Three formulations were studied using two application methods. The acid (DPX-MAT28) was applied as a foliar treatment. DPX-MAT28 was also formulated as an oil soluble liquid using the emulsifying agent didecyl dimethyl ammonium chloride and applied as a basal bark treatment. The methyl ester (DPX-KJM44) was formulated as an emulsifiable concentrate and applied basally for comparison. Dormant saplings approximately 0.5 m tall were obtain from a local grower. Saplings were grown in a greenhouse until new foliage had emerged. For the foliar application, the second fully expanded leaf on the lowest branch was marked and covered. Plants were treated with a non-radiolabeled mixture containing 210 g ai ha-1 of either herbicide and a nonionic surfactant at 0.25% v v-1 using a carrier volume of 300 l ha-1. Following application, marked leaves were treated with 5, 0.5µL spots of radioactive herbicide containing in total 29.29 kBq. For basal bark applications each plant stem was spotted with 10 µL of herbicide mixture containing non-radiolabeled and radiolabeled material and  oil carrier. Plants were dosed with 0.25 mg active ingredient and received 22.56 kBq radiolabeled herbicide. Plants were harvested at 2, 8, 24, or 72 h after treatment (HAT), divided into six parts for foliar treatment or four parts for basal treatments. Parts were dried, weighed, and larger samples ground. Sub-samples were then oxidized using a biological oxidizer. In quaking aspen, foliar applied DPX-MAT28 absorbed radiolabeled material less rapidly than either basal application, reaching a maximum of 9.9% at 72 HAT. Total translocation of applied radiolabeled herbicide was 2.0% at 72 HAT. When applied basally as an oil-soluble liquid, DPX-MAT28 absorption was 48.3% at 72 HAT. Translocation 72 HAT was 13.0% of applied material. The methyl ester basal bark treatment had the greatest absorption and translocation with 54.8% absorbed 72 HAT and 24.0% applied herbicide moving from treated area 72 HAT. Quaking aspen appears to be highly sensitive to aminocyclopyrachlor based on early herbicide symptomology and low absorption and translocation. Basal bark treatment may be a more effective application method for woody shrubs and trees as more herbicide is absorbed and translocated throughout the plant compared to foliar applications.



RESISTANCE OF CONYZA SPP BRAZILIAN BIOTYPES TO GLYPHOSATE. M. Nicolai*1, P. J. Christoffoleti1, J. D. Vassios2, M. S. Melo3, S. J. Nissen2, P. Westra2; 1Univeristy of Sao Paulo - ESALQ - Brazil, Piracicaba, Brazil, 2Colorado State University, Fort Collins, CO, 3University of Sao Paulo, Piracicaba, Brazil (119)

ABSTRACT

Horseweed (Conyza bonariensis) is a common weed in no-till crop production systems in Brazil; however it is becoming problematic because of frequent occurrence of glyphosate resistant (GR) biotypes, and its ability to complete its live cycle as a fall and winter annual weed. Therefore, fall herbicide applications have increased in popularity over the past several years since, among other advantages, allow growers control annual horseweed more effectively compared with spring applications by targeting the weed at a much earlier growth stage. Thus, a field study was conducted in Itapira, SP - Brazil from June 2009 to April of 2010. Sequential treatments were applied initiating immediately after “off season” corn harvest (autumn/winter treatment) with continuous fallow, glyphosate 1080 g ae/ha in association with 2,4-D at 1,005 g ae/ha plus metsulfuron-methyl at 3.6 g ai/ha or diclosulam at 25.2 ai/ha, or flumioxazin 100 g ai/ha, which were followed by spring/summer application of glyphosate 1080 g ae/ha 10 days before soybean seeding (DBS), alone and in association with 2,4-D at 750 g ae/ha or 1,005 or 1,340 g ae/ha plus paraquat + diuron at 450 g ai/ha (3 DBS) or diclosulam at 25.2 g ai/ha, and a check plot. At 27 days after soybean seeding (DAS) all treatments, but the check plot, were sprayed with glyphosate at 1,080 g ae/ha (POST). All the treatments tested controlled more than 95% of the horseweed, except the systems where the autumn/winter treatment was fallow (maximum control obtained 88%) with the spring/summer application of glyphosate at 1,080 g ae/ha + 2,4-D at 1,340 g ae/ha + diclosulam at 25.2 g ai/ha. Soybean yield was similar in all treatments (mean yield 3,473 kg/ha), except for the check treatment (2,003 kg/ha), and the treatment fallow during autumn/winter and glyphosate at 1,080 g ae/ha (10 DBS) (2,833 kg/ha). We believe that winter/fall application of alternative mechanism of action herbicide associated with glyphosate control effectively winter annual horseweed compared with spring applications.




TRANSPIRATION-USE EFFICIENCY COEFFICIENT OF EIGHT WEED SPECIES AS AFFECTED BY FRACTION OF TRANSPIRABLE SOIL WATER AND GROWTH STAGE. V. Mannam*, M. L. Bernards, J. L. Lindquist, T. J. Arkebauer, S. Z. Knezevic, S. Irmak; University of Nebraska-Lincoln, Lincoln, NE (120)

ABSTRACT

Transpiration-use Efficiency Coefficient of seven weed species as Affected by Fraction of Transpirable Soil Water and Growth Stage

Venkatarao Mannam, Mark L. Bernards, John L. Lindquist, Timothy J. Arkebauer, Stevan Z. Knezevic, and Suat Irmak.

Transpiration-use efficiency coefficient (Kc) describes the amount of biomass produced per unit transpiration at a given vapor pressure deficit. Kc values of several crop species are known, but Kc values for weed species have not been reported. A series of two-run greenhouse experiments were conducted at the University of Nebraska-Lincoln, to determine the Kc values of field pennycress, common lambsquarters, pinnate tansymustard and dandelion and how K­c­ values were affected by fraction of transpirable soil water (FTSW) level and plant growth stage. Experiments were conducted as a two-factor factorial design with 4 levels of water stress (0.3, 0.4, 0.7, and 1.0 FTSW) and two harvest times (first bloom and seed maturity). A polyethylene bag was placed in each plastic pot, filled with a predetermined mass of a soil mixture, and planted with one species per pot. After plants attained a predetermined size, polyethylene bag was tightly sealed at the base of each plant to ensure that water loss was occurred only through transpiration. A 5 ml syringe was inserted through the bag and the junction was taped to maintain the seal. Water was added to each pot to bring it to the desired FTSW level, and pots were subsequently weighed daily and brought to the required weight by watering through the syringe. Transpiration that occurred prior to bagging was back-calculated by fitting a polynomial function from 0 d to the first 20 d of measured daily transpiration. One set of plants was harvested at the time of first bloom (vegetative stage) and another set of plants was harvested at seed maturity (complete lifecycle). At harvest, plants were separated into roots and shoots and biomass was measured by oven drying the plant parts. Seasonal average daytime vapor pressure deficit was calculated using photosynthetically active radiation, temperature and relative humidity data from inside the greenhouse. Kc was calculated as the ratio of total biomass to the cumulative transpiration multiplied by the average daytime vapor pressure deficit. 

The effect of FTSW and growth stage (harvest time) on Kc values differed among the four weed species tested. Kc values increased as FTSW levels declined for field pennycress (vegetative growth), common lambsquarters and pinnate tansymustard suggesting that these species were relatively tolerant to water stress, at least during portions of their life cycle. Kc values decreased as FTSW levels declined for dandelion at both harvest times and for field pennycress at seed maturity. This suggests that dandelion is sensitive to drought stress at all growth stages, and that field pennycress is drought sensitive during reproductive growth stages. Growth stage did not affect Kc values for pinnate tansymustard or dandelion, but Kc values decreased between first bloom (vegetative growth) and seed maturity (complete life cycle) for field pennycress and common lambsquarters.  

 




RESISTANCE OF DIGITARIA INSULARIS BRAZILIAN BIOTYPES TO GLYPHOSATE. P. J. Christoffoleti*1, M. Nicolai1, M. S. Melo2, J. D. Vassios3, S. J. Nissen3, P. Westra3; 1Univeristy of Sao Paulo - ESALQ - Brazil, Piracicaba, Brazil, 2University of Sao Paulo, Piracicaba, Brazil, 3Colorado State University, Fort Collins, CO (121)

ABSTRACT

Managing glyphosate-resistant (GR) sourgrass (Digitaria insularis) in a soybean no-till cropping system and in citrus orchards is a growing challenge for Brazilian producers. Sourgrass is an aggressive weed that can reproduce from seed or from short rhizome segments that develop under mature plants. Greenhouse dose–response studies were conducted to determine the resistance level of seven sourgrass populations collected from six agricultural areas in Sao Paulo State, Brazil with a history of repetitive glyphosate use at recommended use rates (include the rate). One susceptible population was included in these studies. Four populations did not differ in their response to glyphosate, when compared to the susceptible population. However, two populations from citrus orchards establishment had an R/S ratio of approximately 7.5. A field study was conducted to determine if a range of post-emergence herbicides applied alone or in combination with glyphosate could provide sourgrass control. This study was initiated in a citrus plantation in September and October 2009.  Herbicides evaluated were clethodim, haloxyfop-methyl, fluazifop-butyl, clethodim + fenoxaprop-p-ethyl, tepraloxydim, diuron + paraquat, ammonium glufosinate, clethodim + glyphosate followed by paraquat + diuron and clethodim + glyphosate followed by ammonium glufosinate. The best control was provided by haloxyfop-methyl at 60 g ai/ha + glyphosate at 1920 g ae/ha, fluazifop-butyl at 125 g ai/ha, fenoxaprop-p-ethyl + clethodim at 100 g ai/ha and tepraloxydim at 100 g ai/ha. Based on biomass comparisons 35 days after application (DAA), control was 99, 98, 99 and 98%, respectively. Other treatments varied from 95% (glyphosate + sethoxydim) to 67% for ammonium glufosinate alone. Glyphosate alone provided only 68% control. Producers will be forced to utilize new herbicides to achieve commercial control of these glyphosate resistant sourgrass populations in the future.




GLYPHOSATE RESISTANCE IN ITALIAN RYEGRASS (LOLIUM MULTIFLORUM) BIOTYPES FROM BRAZIL. F. P. Lamego*1, M. Gallon2, Q. Ruchel2, T. E. Kaspary2, S. T. Peruzzo2, I. B. Pagliarini2; 1Universidade Federal de Santa Maria/Cesnors, Frederico Westphalen, Brazil, 2Federal University of Santa Maria/CESNORS, Frederico Westphalen, Brazil (122)

ABSTRACT

Glyphosate is a broad-spectrum, no selective herbicide widely used to control annual and perennial plant species. In Brazil, it has also been used in no-tillage systems for over 20 years. However, after years of glyphosate use, Italian ryegrass resistant biotypes have been detected in orchards and grain crops, which has forced farmers to search for alternative herbicides. The objectives of this research were (1) to confirm and quantify levels of Italian ryegrass resistance to glyphosate in two suspected biotypes (LOLMU1 and LOLMU2), when compared with a susceptible biotype (LOLMU3), (2) to verify alternative herbicides for glyphosate-resistant biotypes control, and (3) to compare the plant growth between resistant and susceptible Italian ryegrass biotypes. Seeds of LOLMU1 and LOLMU2 were collected in two crop fields located in Rio Grande do Sul state, southern Brazil. The susceptible seeds were collected from a field without herbicide application. Three experiments were conducted in a greenhouse at the Universidade Federal de Santa Maria/Cesnors, in 2010. Dose response curves to glyphosate were generated in a whole-plant assay. Plants at the three-leaf stage were sprayed with glyphosate equivalent to 0, ½, 1, 2, 4, 8 and 16x the full herbicide dose. In a second experiment, sethoxydim (184 g a.i ha-1) and paraquat (300 g a.i ha-1) were evaluated as alternative herbicides to control glyphosate-resistant Italian ryegrass biotypes. The plant height was measured every week up to 42 days after emergence (DAE) in two plants per pot in the greenhouse, when were sectioned into roots and shoots. Data confirmed the two suspected biotypes were resistant to glyphosate. LOLMU1 and LOLMU2 showed, respectively, 3.5- and 3.6-fold resistance to the herbicide. Paraquat and sethoxydim herbicides showed 100% of control for the resistant and susceptible biotypes. LOLMU3 showed superior plant height when compared with LOLMU1 and LOLMU2. However, there was no difference in shoot, root and biomass between LOLMU3 and LOLMU2 for up to 42 DAE. Experiments related to seed production and seed germination comparing glyphosate-resistant and susceptible Italian ryegrass biotypes are in progress.

 

 




INVOLVEMENT OF CYTOCHROME P450 IN BENSULFRONMETHYL RESPONSIVE PHOTON EMISSION FROM RICE CELLS. H. Nukui*, H. Iyozumi, K. Kato, C. Kageyama; Shizuoka Research Institute of Agriculture and Forestry, Iwata, Japan (123)

ABSTRACT

Living organisms generate ultraweak photon emission, so-called biophotons, in response to various stresses. Previously we reported that sulfonylurea (SU)  herbicide resistant weed biotypes generate more biophotons than susceptible ones when treated with SU herbicide (Inagaki et al., 2007; Inagaki et al., 2008). Though a precise molecular mechanism of biophoton generation is still unclear, it is considered that chemical reactions such as oxidation are the source of energy for biophoton generation. Application of cytochrome P450 monooxygenase inhibitors suppressed photon emission from bensulfronmethyl (BSM) treated leaf segments of rice. This suggests that detoxification of BSM by cytochrome P450 may be involved in BSM responsive photon emission from rice leaf segments (Inagaki et al., 2007).

To clarify the involvement of cytochrome P450 in BSM responsive photon emission, we made transgenic rice cultured cell line having suppressed gene expression of CYP81A6, a rice cytochrome P450 gene responsible for BSM tolerance, and treated the cells with BSM.

BSM treatment to rice cells induced two-peaked photon emission in dose dependent manner. In CYP81A6 suppressed line (CYP81A6i), BSM responsive photon emission was suppressed. Growth inhibition test revealed that CYP81A6i was about ten fold sensitive to BSM than control line. Though the application of branched chain amino acids (Val, Leu, Ile) to CYP81A6i recovered the cell growth inhibited by BSM, it had no effect on recovering the suppressed BSM responsive photon emission. These results indicate that it is not the enhanced inhibition of branched chain amino acids biosynthesis attributed to increased BSM sensitivity but reduced BSM detoxification by cytochrome P450 that caused suppression of BSM responsive photon emission.




INVESTIGATIONS INTO SUSPECTED GOOSEGRASS RESISTANCE TO GLYPHOSATE IN MISSISSIPPI. V. K. Nandula*1, W. Molin2; 1Mississippi State University, Stoneville, MS, 2USDA-ARS, Stoneville, MS (124)

ABSTRACT

Glyphosate-resistant goosegrass has been documented in Malaysia and Columbia. In 2009, a goosegrass population near Stoneville, Washington County, Mississippi, bordering a a field planted to glyphosate-resistant cotton for eight years, had survived repeated applications of glyphosate at 0.84 kg ae/ha. Seed from several plants was bulked and screened for resistance to glyphosate at 0.84 kg/ha. Plants that survived were taken to maturity and a glyphosate dose response experiment was conducted using the second generation seed. A susceptible biotype was included for comparison. Based on % control of 5- to 8-cm-tall treated plants measured 3 wk after treatment (WAT), the GR50 values for the resistant and susceptible biotypes were 0.66 and 0.48 kg/ha glyphosate. Further, an acid formulation of glyphosate at 0.84 kg/ha provided 85 and 100% control of the resistant and susceptible biotypes, respectively. Resistant and susceptible populations, obtained from a different section of the field, had GR50 values of 0.46 and 0.2 kg/ha (based on % control of 5- to 8-cm-tall treated plants 3 WAT) and 0.42 and 0.28 kg/ha (based on % shoot fresh weight reduction of 5- to 8-cm-tall treated plants 3 WAT), respectively. Efficacy of non-glyphosate mode of action herbicides on these resistant and susceptible populations was 93 and 95% with clethodim, 98 and 98% with fluazifop-P, 100 and 100% with paraquat, and 78 and 80% with glufosinate, respectively, on 5- to 8-cm-tall treated plants . An additional goosegrass population from a different location in Washington County, Mississippi is currently being screened for resistance to glyphosate.




LOCALIZATION OF AN ABC TRANSPORTER IN A GLYPHOSATE RESISTANT MUTANT OF CONYZA. R. E. Hoagland*1, W. Molin2, K. C. Vaughn2; 1USDA-ARS, CPSRU, Stoneville, MS, 2USDA-ARS, Stoneville, MS (125)

ABSTRACT




PANICLE CHANGES IN RICE RESULTING FROM MSMA APPLICATION. H. Belefant-Miller*; USDA, Stuttgart, AR (126)

ABSTRACT





GLYPHOSATE RESISTANCE CONFIRMED IN WATERHEMP FROM MISSISSIPPI. V. K. Nandula*1, C. H. Koger1, J. A. Bond1, R. C. Bond1, T. W. Eubank1, K. N. Reddy2, J. D. Ray2; 1Mississippi State University, Stoneville, MS, 2USDA-ARS, Stoneville, MS (127)

ABSTRACT

A waterhemp population in a glyphosate-resistant soybean field located in southern Washington County, Missisippi was suspected to be resistant to glyphosate. Seed from this population was collected in the summer of 2008 and 10-cm tall plants screened with glyphosate at 0.84 kg ae/ha. Plants that survived 3 wk after treatment (WAT) were allowed to randomly cross with each other to produce the second generation seed. Preliminary screening experiments indicated that the second generation plants survived a glyphosate treatment of 0.84 kg/ha. Dose response experiments were conducted on 5- to 8-cm tall waterhemp plants by treating with glyphosate at 0, 0.21, 0.42, 0.84, 1.68, and 3.36 kg/ha. Percent control ratings were recorded 3 WAT. A susceptible population was included for comparison. GR50 (glyphosate dose required to cause a 50% reduction in growth of treated plants) values of the resistant (R) and susceptible (S) populations were 1.28 and 0.28 kg/ha glyphosate indicating a five-fold level resistance in the R population compared to the S population. The S population accumulated more shikimate than the R population, measured via a leaf-disc assay. Among several non-glyphosate herbicide chemistries evaluated for efficacy on the R population, only 2,4-D and mesotrione provided more than 90% control 3 WAT.




COMPARISON OF BIOCHAR WITH ACTIVATED CHARCOAL ON SOIL ACTIVITY OF ATRAZINE AND METRIBUZIN. D. L. Shaner*1, R. A. Boydston2, L. Krutz3, H. Collins4; 1USDA, Fort Collins, CO, 2USDA-ARS, Prosser, WA, 3USDA-ARS, Stoneville, MS, 4USDA, Prosser, WA (128)

ABSTRACT

Biochar is a fine-grained, carbon enriched product created when biomass (e.g. wood waste, manures) is burned at relatively low temperatures and under an anoxic atmosphere.  Biochar is being added to soil help retain nutrients and increase water holding capacity. Biochar may also tie up herbicides similar to activated charcoal (AC), negating the herbicide’s efficacy.  In this study the effect of biochar was compared to AC on the binding and efficacy of atrazine and metribuzin in a Quincy Sand and a Warden Sandy Loam.  While biochar did increase the binding of both herbicides to both soil, it was not as effective as activated charcoal.  Even 22.5k kg ha-1 of biochar was less effective than 224 kg ha-1 of AC.  AC completely safened atrazine and metribuzin on oats in both soils at 1.12 kg ha-1 and 0.56 kg ha-1, respectively.  Biochar at 22.5k kg ha-1 decreased the pre-emergent activity of atrazine on oats by approximately 20-and 5-fold in the sand and sandy loam soils, respectively.  The pre-emergent activity of metribuzin was decreased approximately 10- and 2.5-fold at the same rate of biochar in the sand and sandy loam soil, respectively. 




RESPONSE OF PENNSYLVANIA NATIVE PLANT SPECIES, CORN AND SOYBEAN TO TANK MIXES OF DICAMBA AND GLYPHOSATE. D. Olszyk*1, T. Griffin2, A. Ramsower3, T. Pfleeger2, E. Lee2, M. Plocher4; 1US EPA, 97404, OR, 2US EPA, Corvallis, OR, 3EPA GRO Fellow, Yuma, AZ, 4Dynamac Corp., Corvallis, OR (129)

ABSTRACT

Crops such as soybean are being genetically modified to be tolerant to multiple herbicides, such as dicamba and glyphosate, in order to allow treatment with several herbicides to control the development of herbicide resistance in weeds. However, with increased use of multiple-herbicide tolerant plants, non-target plants may be subjected to aerial drift from two herbicides used in combination, instead of just one. Of particular concern are non-target native plants, although crops which have not been genetically modified for tolerance to both herbicides may also be at risk. We evaluated the response to herbicides for four species of native plants found in eastern and mid-western U.S, Andropogon gerardii, Oenothera biennis, Polygonum lapathifolium, and Tridens flavus and non-herbicide resistant soybean (Glycine max, Oregon cultivar14) and corn (Zea mays, Pioneer Pioneer 39J26); which may be at risk from drift of glyphosate and dicamba used on tolerant soybeans. Herbicide concentrations representing aerial drift were used, 0.1 and 0.03 or 0.01 x field application rates (FAR) of approximately 830 and 563 g HA-1 for glyphosate and dicamba, respectively. Plants were grown in small plots in the field to have more realistic plant growth and exposure conditions than may be found in a greenhouse. In general, glyphosate or dicamba at 0.1 x FAR individually reduced plant growth. Lower concentrations of the individual herbicides and herbicide mixes produce some, but inconsistent plant responses. This study indicated that levels of glyphosate and dicamba characteristic of potential herbicide drift concentrations can represent risks to growth of non-target crop and native plants.



DEGRADATION OF SAFLUFENACIL AS AFFECTED BY MOISTURE CONTENT AND SOIL CHARACTERISTICS. E. R. Camargo*1, S. A. Senseman1, R. Haney2, J. B. Guice3, G. McCauley4; 1Texas A&M University, College Station, TX, 2United States Department of Agriculture, Temple, TX, 3BASF Corporation, Winnsboro, LA, 4Texas AgriLife Research, Eagle Lake, TX (130)

ABSTRACT

Saflufenacil is a new herbicide for residual preemergence broadleaf weed control in corn and other crops. Experimental formulations of saflufenacil were tested in rice demonstrating effective control of dicotyledon weeds. However, before this herbicide can be used in production rice, environmental aspects associated with its behavior and fate in soil need to be investigated. No work has been published investigating degradation of saflufenacil in flooded conditions similar to those found in an irrigated rice field. The objective of this study was to evaluate saflufenacil persistence and degradation in soils from different rice regions under flooded and non-flooded conditions. Air-dried soil samples from Eagle Lake, TX (Nada fine sandy loam), Beaumont, TX (Morey loam), Crowley, LA (Crowley silt loam), and Gilbert, LA (Gilbert silty clay) were used in the study. Samples of each soil (10 g) were placed in a round bottom centrifuge tube, re-wetted to re-establish microbial activity, and pre-incubated in the dark for 15 days prior to herbicide addition. Stock solutions were prepared using technical grade saflufenacil dissolved in acetonitrile. Saflufenacil was applied in pre-incubated samples at the rate of 2000 g ha-1 (2.67 µg g soil -1). Before adding the water treatments, the saflufenacil solution was thoroughly mixed into the soil. The amount of water added in the non-flooded (field capacity) and flooded (saturation) treatments was determined using a water retention curve. In the flooded incubation, samples had a layer of water, simulating a flooded rice paddy. Tubes were then loosely caped and incubated at 24.8 C (± 0.5) in the dark. Upon experiment initiation, samples were removed at 0, 1, 3, 7, 14, 21, 30, 45 days. An accelerated solvent extraction (ASE) method was developed and used to extract saflufenacil from soil samples. Extractions from soil were analyzed with a liquid chromatography equipped with a photodiode array detector (LC-PDA). Microbial respiration was determined hourly for 30 days. Samples (30 g) were placed in a sealed chamber coupled with an infrared CO2 detector allowing continuous reading of carbon mineralization. Carbon mineralization was higher under field capacity conditions. Rate of cumulative carbon mineralization was 1.5 to 7.2-fold greater depending on the soil. Soil saturation under the flooded treatment depleted oxygen in the soil environment thereby reducing microbial respiration. Concentration of saflufenacil decreased more rapidly in field capacity treatments, except for Morey soil. Herbicide half-life was 2.1, 2.5, and 3.4 times shorter under field capacity treatments for Nada, Crowley, and Gilbert soils, respectively. Half-life averaged among soils was 59.2 and 32.7 days for saturated and field capacity, respectively. Reduction of aerobic microbial activity resulted in slower degradation of saflufenacil under saturated treatments. Crowley soil had the fastest degradation among soils in both moisture treatments. Results indicated that saflufenacil persistence in the environment would be 2 to 3 times longer under flooded conditions.




SORPTION-DESORPTION OF AMINOCYCLOPYRACHLOR IN SELECTED BRAZILIAN SOILS. R. S. Oliveira Jr.*1, W. C. Koskinen2, D. G. Alonso1; 1Universidade Estadual de Maringá, Maringá, Brazil, 2USDA-ARS/University of Minnesota, St. Paul, MN (131)

ABSTRACT

Aminocyclopyrachlor sorption and desorption was investigated in 14 soils from Brazil, representing a range of pH, and organic carbon (OC) and clay contents. Sorption kinetics demonstrated that soil-solution equilibrium was attained in a 24-h period. Freundlich equation adequately described behavior of aminocyclopyrachlor in soil. Freundlich sorption coefficient (Kf) values ranged from 0.06 to 1.64 and 1/n values for sorption were equal to or higher than 0.90. Sorption was correlated to OC (Kf,oc ranged from 11 to 64) and clay contents. The lowest sorption was found for soils with very low OC contents (0.50-0.65%) and loamy-sand to sand textures. The 1/n values for desorption were lower than those observed for sorption, suggesting that aminocyclopyrachlor sorption by soil was not reversible; hysteresis coefficients ranged from 0.13 to 0.74. The results suggest that although aminocyclopyrachlor would be very mobile based on its sorption coefficients, its potential mobility may be overestimated due to the hysteretic desorption.




HERBICIDE IMAZETHAPYR + IMAZAPIC CARRYOVER TO NON-TOLERANT RICE AS AFFECTED BY THE THICKNESS OF THE SOIL PROFILE. A. Bundt*, L. de Avila, D. Agostinetto, M. Nohatto, M. Ramos, T. Vieira Duarte, A. Langaro; Universidade Federal de Pelotas, Pelotas, Brazil (132)

ABSTRACT

Rice soils normally have shallow hardpans, and depending on how shallow it is, it can hinder the movement of pesticides in the soil, and can affect the carryover of the herbicide, depending on the depth of the hardpans. For this reason, it was carried out an experiment aiming at evaluating the effect of the depth of the soil profile on the carryover of imidazolinone herbicide to non-tolerant rice. The herbicide tested was a formulated mixture of imazethapyr and imazapic (75 + 25 g ai L- 1). The plots were 20‑cm diameter PVC pipes at the corresponding soil profile tickness (15, 20, 30, 40, 50 and 65 cm). The experiment was divided in two parts, the first in the 2008/09 growing season, it was grown Clearfield rice with herbicide application (1.0 L ha-1 of the formulated mixture) and the second in the 2009/10 growing season, were grown non-tolerant rice. It was evaluated non-tolerant rice plant injury at 7, 14, 21 and 28 days after emergence (DAE), shoot dry weight (grams) and plant height (cm) at 32 days after emergence. The formulated mixture of imazethapyr and imazapic persists in the soil and cause injury to non-tolerant rice sown 280 days after herbicide application, reducing plant dry weight. The shallower the soil profile, the higher the injury of the herbicide to non-tolerant rice.

 




DISSIPATION OF PYROXASULFONE AND S-METOLACHLOR OVER TWO YEARS IN TWO FIELDS. E. P. Westra*1, D. L. Shaner2, P. Westra1; 1Colorado State University, Fort Collins, CO, 2USDA, Fort Collins, CO (133)

ABSTRACT

Pyroxasulfone is a new soil applied herbicide that is being developed for use in corn, wheat, soybeans and other crops. It is important to have an understanding of how this new herbicide behaves in the field. Studies on the field dissipation and soil binding of pyroxasulfone and s-metolachlor were done in 2009 and 2010. Field dissipation studies comparing the behavior of pyroxasulfone with s-metolachlor were conducted at 2 locations in northern Colorado in sunflowers. Pyroxasulfone was applied at 0.28 kg ai/ha, and s-metolachlor at 1.67 kg ai/ha. The herbicides were extracted from the soil with toluene and analyzed on a G.C. mass spectrometer to quantify herbicide concentrations. The 2010 growing season received higher precipitation compared to the 2009. The higher moisture levels resulted in faster dissipation of both herbicides in 2010 compared to 2009. These results illustrate the importance of soil moisture on dissipation rates for both herbicides. The binding of pyroxasulfone to soil (Kd) was compared to the binding of dimethenamid and s-metolachlor across 20 soils. s-Metolachlor had the highest Kd values, (0.34 to 6.35) whereas pyroxasulfone had the lowest (0.13 to 3.22) Kd and was similar to dimethenamid   These results suggest that greater amounts of pyroxasulfone will be found in the soil water compared to metolachlor.




IMPACT OF THE QUALITY OF ORGANIC AMENDMENTS ON SIZE AND COMPOSITION OF THE WEED SEEDBANK. B. De Cauwer, R. Bulcke*, D. Reheul; Ghent University, Ghent, Belgium (134)

ABSTRACT

In addition to improving the soil quality, organic amendments of soils may affect weed seed survival, emergence, growth and reproduction. This study evaluated the effects of applications of different qualities of organic amendments on size and composition of the weed seed bank in a field under sequential cropping over four years. Fertilisation systems tested included: farmyard manure, vegetable fruit and garden waste compost, two types of farm compost differing in carbon:nitrogen (C:N) ratio and finally cattle slurry and mineral fertiliser. All organically amended plots received equal amounts of C. Crop growth was equalised on all plots by applying extra mineral N. Seed bank sampling took place in May 2009 to a depth of 10 cm. The weed seed bank was analysed with the seedling emergence method. Despite equal crop growth in fertilised plots, total seed bank density was lowest in plots amended with compost with low C:N ratio and highest in slurry amended plots. Observed differences in seed bank densities reflected differences in soil organic carbon content and microbial biomass. At plot level, hard-coated seeds in the seedbank (e.g. Chenopodium spp.) were inversely related to soil microbial activity. Observed differential responses of species to applied fertilisers might be attributed to interspecific differences in resistance against microbial seed degradation. Compost based fertilisation systems are sustainable tools for incorporation into integrated weed control strategies aiming at depleting the weed seed bank. benny.decauwer@ugent.be



WEED SUPPRESSION AND SOIL NITROGEN BENEFITS ASSOCIATED WITH LEGUME COVER CROP-WINTER WHEAT INTERCROPS. R. E. Blackshaw*, L. Molnar, J. Moyer; Agriculture and Agri-Food Canada, Lethbridge, AB (135)

ABSTRACT

A series of multi-year field experiments were conducted at Lethbridge, Alberta to determine the merits of establishing alfalfa, red clover, or Austrian winter pea cover crops in fall or in spring with winter wheat. Main plots were the various under-seeded legumes and subplots were the seeding date of the legumes. Data collected included winter wheat and cover crop densities, weed biomass, winter wheat yield, soil nitrogen, and following spring canola yield. Spring-planted legumes emerged well within the established winter wheat crop but their growth and N fixation was very limited under these conditions. Fall-planted red clover suffered considerable winter kill in 2 of 3 experiments. Fall-planted winter pea survived the winter conditions in all years but reduced winter wheat yield by 23 to 37% compared to the no cover crop control. In contrast, fall-planted alfalfa exhibited good winterhardiness, did not reduce winter wheat yield, and contributed an extra 18 to 20 kg ha-1 of available soil N at the time of seeding the following spring canola crop. Additionally, fall-planted alfalfa caused a 50-60% reduction in the biomass of flixweed (Descurainia sophia), annual sowthistle (Sonchus oleraceus) and kochia (Kochia scoparia). Succeeding canola yield was increased in 2 of 3 experiments with the alfalfa-winter wheat intercrop; primarily due to higher soil nitrogen levels. Further research is warranted to better understand the agronomic and economic benefits of alfalfa-winter wheat intercrops under a wider range of environmental conditions.




WEED REMOTE SENSING USING LEDS AS SPECTRAL SELECTIVE LIGHT DETECTORS. C. Weber, H. A. Acciaresi*; Fac. Cs. Agrarias y Ftales (UNLP), La Plata, Argentina (136)

ABSTRACT

Remote sensing has been commonly considered as an effective technique in developing precision agriculture tools. Ground based and satellite spectral sensors have wide uses to retrieve remotely quantitative biophysical and biochemical characteristics of vegetation canopies as well as vegetation ground cover. Usually in-field remote sensing technologies use either a combination of interferential filters and photodiodes or different compact spectrometers to separate the spectral regions of interest.

We present a new development of a sensor with LEDs used as spectrally selective photodetectors. Its performance was compared with a photodiode-filter sensor used in agronomic applications. Subsequent measurements of weed cover degree were performed and compared with other methodologies. Results show that the new LEDs based sensor has similar features that conventional ones to determining the weed soil cover. LEDs based sensor has comparative advantages related its very low manufacturing cost and its robustness compatible with agricultural field applications.




NEW TARGET SITE MUTATION IN A GLYPHOSATE RESISTANT SUMATRAN FLEABANE (CONYZA SUMATRENSIS). F. González-Torralva1, J. Gil-Humanes2, F. Barro2, R. De Prado*1; 1University of Córdoba, Córdoba, Spain, 2Instituto de Agricultura Sostenible CSIC, Córdoba, Spain (137)

ABSTRACT

New Target Site Mutation in a Glyphosate Resistant Sumatran Fleabane (Conyza sumatrensis)

1Fidel González-Torralva, 2Javier Gil-Humanes, 1Antonia Mª. Rojano-Delgado, 1Hugo E. Cruz-Hipolito, 2Francisco Barro, 1Rafael De Prado.

1University of Cordoba, Cordoba, Spain.

2Institute for Sustainable Agriculture (CSIC), Cordoba, Spain.

In Spain three species of Conyza have been reported as glyphosate resistant: C. bonariensis, C. canadensis and C. sumatrensis. Assays carried on C. sumatrensis showed the dose-response curve with an ED50 of 60 fold higher in the R biotype than the S one. With the aim to determine the presence of target site mutations, the EPSPS1, EPSPS2 and EPSPS3 isoforms were characterized. Preliminary results have shown two amino acid changes in the protein of the R biotype. In the EPSPS1 did not appear amino acid changes; the EPSPS2 showed a Proline to Threonine substitution in the R biotype at the position 108, while the EPSPS3 showed a Valine to Leucine substitution in the R biotype at the position 63. Those results could explain the high glyphosate resistance level in the R biotype.




GLYPHOSATE RESISTANCE BIOMARKER: DIGITARIA INSULARIS AS A CASE OF STUDY. A. M. Rojano1, L. Bianco de Carvalho2, F. Priego-Capote1, M. Luque de Castro1, R. De Prado*1; 1University of Córdoba, Córdoba, Spain, 2University of Sao Paulo, Sao Paulo, Brazil (138)

ABSTRACT

Digitaria insularis: a Case of Study of Glyphosate Resistance Biomarker

 

A.M. Rojano-Delgado1, F. González-Torralva1, H.E. Cruz-Hipólito1, Leonardo Bianco Carvalho2, F. Priego-Capote3, M.D. Luque de Castro3, R. De Prado Amián1.

 

1Department of Agricultural Chemistry, C-3 Building, Campus of Rabanales, University of Córdoba, E-14071 Córdoba, Spain.

2Department of Applied Biology to Agropecuary, São Paulo State University, Brazil 14884-900.

3Department of Analytical Chemistry, Annex C-3, Campus of Rabanales, University of Córdoba, E-14071 Córdoba, Spain.

 

 

Sourgrass is a perennial weed infesting anual and perennial crops in Brazil. Three biotypes (R1, R2 and R3) of sourgrass suspected of being glyphosate-resistant and another one (S) from a natural area without glyphosate application in Brazil, were tested for detection of resistance to glyphosate based on dose-response, shikimic acid and glyoxylate assays. Dose-response assay indicated a resistance factor of 2.33, 3.90 and 3.89 for biotypes R1, R2 and R3, respectively. The confirmation of the resistance to glyphosate was corroborated by shikimic acid and glyoxylate accumulation assays. Shikimic acid results showed that the biotype S accumulated 3.3, 5.0 and 5.7 times more than the biotypes R1, R2 and R3, respectively, 168 hours after treatment; while glyoxylate accumulation was observed in the biotype S since  24 hours after  treatment. On the contrary, the other resistant biotypes (R1, R2 and R3) presented  a decrease in the amount of this compound. The results show that the response of the glyoxylate test is faster than the shikimic acid test with similar results. The response found in the three assays to glyphosate-resistance in Digitaria insularis was: R3=R2 > R1 > S.




RESPECT THE ROTATION: A COMPREHENSIVE PARTNERSHIP TO PRESERVE HERBICIDE AND TRAIT TECHNOLOGY. J. Rutledge*; Bayer CropScience, Research Triangle Park, NC (139)

ABSTRACT

Good stewardship practices enable growers to prevent, manage or delay the spread of weed resistance and protect all useful technologies.  It is the right thing for crop production agriculture to preserve the utility of glyphosate and properly steward other technologies.

Respect the Rotation is a proposed partnership among all sectors of the agricultural industry to establish a comprehensive initiative to drive industry-wide support for weed management stewardship to preserve trait and herbicide technology.

Working together, the weed science, grower, consultant, government, and commodity communities can better steward weed management technology, preserve conservation tillage opportunities and promote sustainable and profitable row crop production.




WEED POPULATION DYNAMICS AND ECONOMICS: OPTIMIZING WEED MANAGEMENT IN ORGANIC SMALL GRAINS. L. N. Kolb*; University of Maine, Orono, ME (140)

ABSTRACT




TILLAGE AND COVER CROP EFFECTS ON WINTER ANNUAL WEEDS IN VEGETABLE CROPPING SYSTEMS. D. C. Brainard*, B. E. Henshaw, Z. Hayden, M. Ngouajio; Michigan State University, East Lansing, MI (141)

ABSTRACT

Increased adoption of reduced tillage practices in combination with rising winter temperatures may be contributing to increases in problematic winter annual weeds in the North Central region.  These species can interfere directly with winter annual and perennial crops and can act as “biological bridges” for pests of summer annuals.  Winter cover crops provide a potentially valuable tool for suppressing winter weeds, while protecting and improving soil characteristics.  The objective of our research was to assess the effects of tillage (moldboard plow versus strip tillage) and cover crops (none, cereal rye, hairy vetch, and 50:50 rye-vetch mixtures) on winter annual weed communities within vegetable cropping systems.  Towards that end, weeds were monitored in multiple field trials on sandy soils in Michigan.  In most cases, strip-tillage resulted in increases in winter annual weeds, including several known hosts of economically important pests in the Brassicaceae and Asteraceae families.  Cover crops helped suppress winter annuals in both conventional and strip-tillage systems, with reductions in weed biomass per plant ranging from 65-98% for rye and rye-vetch, and from 0-85% for vetch alone, compared to bare soil.   Suppression of weed density by cover crops was more variable, ranging from 0-97% depending on year, cover crop, and weed species.   Our results suggest that adoption of reduced tillage systems in vegetable crops is likely to result in increases in winter annual weed densities, and that alternative weed management practices—including greater reliance on winter cover crops—will be useful for minimizing the negative effects of these problematic species.




ECONOMICS OF USING HAND-HELD FLAME CULTIVATORS FOR WEED MANAGEMENT IN CRANBERRY. H. A. Sandler*, K. M. Ghantous; UMass Cranberry Station, East Wareham, MA (142)

ABSTRACT

Flame cultivation is a nonchemical method of weed control where target plants are damaged or eradicated by brief exposure to high temperature. The utility of flame cultivation on perennial weeds in cranberry (Vaccinium macrocarpon) systems is currently being investigated to determine if it could be a useful practice for cranberry weed control. Our work is focused on evaluating the use of flame cultivation as a spot-treatment for control of dewberry (Rubus spp.), sawbrier (Smilax glauca), dodder (Cuscuta gronovii) and rushes (Juncus spp.). In addition to collecting efficacy data, we wanted to determine and compare the cost of using hand-held flame cultivators (FC) to the conventional management of using glyphosate wiper applicators. Three hand-held FC were considered in this comparison: infrared (IR), infrared with spike (IRS), and open flame, (OF).

The hourly costs of operating any of the 3 torches tested was comparable to the hourly cost of weed wiping (i.e., using a hockey stick applicator) with glyphosate. Labor costs were assumed to be $12 per hour and the impact of weed patchiness across the farm was assumed to affect each weed control method equally. The equipment costs of the hand-held FCs are very similar to one another; the weed wiper is much less expensive ($200 to $250 for the torches compared to $40 for the weed wiper). The cost of fuel expended for 1 hr of torch operation was comparable for the three FCs but the cost of the herbicide that would be used in 1 hr of wiper application was $7 to $8 more than the propane to run the FCs. 

A square meter was selected as the base unit area by which to calculate the costs associated for the treated area for all management options. Actual management costs would most likely vary due to factors such as operator skill, patchiness of the weeds (i.e., how far would one need to walk between applying a treatment), how much fuel or herbicide a person might use on any particular weed or location, etc. Any deviations from assumptions could be inserted into our formulas to recalculate the actual cost to a grower on their particular farm.

            As a spot-application on cranberry farms, use of the OF is comparable economically to the standard weed management practice of spot-applications of weed wiping with a hockey stick applicator. Our research showed a dose response (increased control with increased duration), so we would likely recommend growers use at least the medium (6 sec), if not the high (9 sec) duration for weed management with the OF hand-held applicator. At the medium OF duration, costs are equivalent with glyphosate applications ($0.37 vs. $0.32 per m2, respectively). Use at the high duration would still be competitive ($0.56 per m2). The IR and IRS are more expensive relative to both the OF and the wiper applicator. At the long duration for the IR flame cultivators (45 sec), the costs are 8 times higher ($2.60 per m2) than both OF at medium duration and the glyphosate wipes.

 

 

hsandler@umext.umass.edu

 




REPLACING METHYL BROMIDE ON GEORGIA FARMS. L. M. Sosnoskie*1, T. M. Webster2, A. S. Culpepper1; 1University of Georgia, Tifton, GA, 2USDA-ARS, Tifton, GA (143)

ABSTRACT

Replacing Methyl Bromide on Georgia Farms

L. M. Sosnoskie, T. M. Webster and A. S. Culpepper

 

In GA, the loss of MB directly impacts the production and profitability of pepper, eggplant, and tomato. Three fumigant alternatives, methyl iodide plus chloropicirn (MI), dimethyl disulfide plus chloropicrin (DMDS), and Telone II plus chloropicrin plus Vapam (3-WAY) have exhibited promising results in small plot trials for the control of pests (weeds, pathogens, nematodes) in plasticulture production. The objective of this study was to determine if MI, DMDS and the 3-WAY are alternatives to MB with respect to weed control in large, on-farm trials.

 

The study was conducted on three commercial farms located in Colquitt, Echols, and Tift Counties in GA during the spring of 2007. Fumigants were applied between late January and mid February. MB 57:43 was applied broadcast at rates of 357 to 443 lb/A under LDPE mulch, MI 50:50 was applied broadcast at rates of 170 to 174 lb/A under high barrier mulch (Blockade), and DMDS 79:21 was applied broadcast at rates of 71 to 76 gal/A under LDPE mulch; all were injected 8 inches deep with 3 knives on a 32 inch bedtop using a super bedder plastic layer. For the 3-WAY system, Telone II was applied broadcast at rates of 10 to 16 gal/A, chloropicrin was applied broadcast at rates of 146 to 151 lb/A, and Vapam was applied at 75 gal/A, all under LDPE mulch. Telone was injected 10 to 12 inches deep using three knives on a Yetter applicator, chloropicrin was applied with the super bedder plastic layer 8 inches below the bed top with 3 knives and Vapam was injected 4 inches deep and 4 inches apart with rolling blades placed on the plastic layer. Soil temperatures ranged from 55 to 66 F at the point of fumigation; soil moisture ranged from 60 to 73%. Treatments were replicated 4 times at each site. Plots ranged from 0.13 to 0.41 A in size. Bell peppers were transplanted in March. Pepper height, pepper stand and weed emergence were evaluated throughout the season. Fruit were harvested according to grower practices and processed through commercial packing houses. Numbers of boxes for each fruit size for each plot were counted.

 

Pepper stands and heights did not differ between treatments. Nutsedge spp and livid amaranth were the predominant weeds in the study. There were no differences in weed control among fumigant treatments at the Colquitt County farm; compared to a check plot, all fumigants reduced weed populations by 99%. Nutsedge and livid amaranth densities were significantly greater in the DMDS (46 to 213 plants/A) treatment as compared to the MB (2 to 60 plants/A) standard at the Echols County and Tift County sites. The MI and 3-WAY treatments did not differ from the MB standard with respect to weed control at both sites. Yield differences were only noted at the Tift County farm.  The mean number of boxes of Jumbo fruit produced (over 4 harvests) in the DMDS (974 boxes/A) treatment was reduced relative to the MB (1011 boxes/A) standard; the reduction in yield was attributed to weed competition. Increased production of Jumbo (1087 boxes/A) and chopper (234 boxes/A) fruit was observed in the 3-WAY system relative to the MB (1011 and 176 boxes/A, respectively) standard. This increase was counterbalanced by a reduction in the number of Extra large and Large fruit, with the total economic value of the 3-WAY and MB systems being similar. Although labeled for use on peppers in 47 states, the current price of MI makes it cost prohibitive for GA growers. DMDS was registered for use in Georiga during the fall of 2010.  Efforts from this and other studies have shown that a DMDS system must include herbicides and must be applied under a high barrier mulch to provide weed control and yields similar to MB or 3-WAY systems.  In 2010, the 3-WAY was applied on over 70% of Georgia’s fumigated acreage.




BRASSICA GENOTYPE AND PLANTING TIME INFLUENCE WEED CONTROL AND PUMPKIN YIELD. J. B. Masiunas*, D. Anderson, J. DeDecker; University of Illinois, Urbana, IL (144)

ABSTRACT

Weed control in pumpkins is dependent on clomazone, ethalfluralin and halosulfuron. Recently, ALS-resistant waterhemp has become a problem in pumpkin production areas. Also methods to control soil-borne pathogens are needed. Brassica species contain glucosinolates that upon tissue damage through soil incorporation are converted into isothiocynates and other biofumigant compounds. Our objective was to determine if Brassica species could modify weed populations or delay weed emergence without injurying pumpkin. We evaluated fall and spring planted mustard species (planted every two weeks from September 1 to October 30 and March 15 to May 15. The cultivars evaluated included oilseed radish, forage turnip, rapeseed, Ida Gold, Pacific Gold, Florida Broadleaf, Tilney, and Red Giant. Mustard biofumigants did not shift weed species or delay emergence. Applications of standard preemergence herbicides was necessary to prevent weed competition that caused stunting of pumpkins and reduced yields. Rapeseed overwintered.  Plantings of mustards in September produced substantial biomass and inhibited winter annuals and early spring weeds but had no effect on weeds such as Amaranthus species emerging with pumpkins.



RYE AND VETCH MANAGEMENT FOR NO-TILL SNAP BEAN PRODUCTION. R. A. Boydston*1, M. M. Williams2; 1USDA-ARS, Prosser, WA, 2USDA-ARS, Urbana, IL (145)

ABSTRACT

Planting no-till into cover crop residues left on the soil surface offers benefits of suppressing weeds, reducing soil erosion, and eliminating trips through the field. Adequate suppression of cover crops to prevent competition with the main crop can be challenging, particularly in organic systems where synthetic herbicides are not allowed. Three cover crop kill methods utilizing a roller-crimper were evaluated in studies conducted in Prosser, WA and Urbana, IL in 2009 and 2010. Cereal rye was planted alone and in combination with common vetch or hairy vetch at Prosser and Urbana, respectively. Cover crops were rolled and crimped at rye anthesis or later either once, twice, or once plus an application of glyphosate (rye and rye/vetch mix) or carfentrazone (vetch). Rolling and crimping once killed cereal rye from 91 to 99% over both locations and years and was not significantly improved by rolling a second time in 3 of 4 site-years. Applying glyphosate after rolling and crimping completely killed rye. Common vetch was suppressed 40 to 51% and hairy vetch 25 to 39% with one pass of a roller-crimper and a second pass only slightly improved vetch kill. Carfentrazone applied after rolling and crimping did not improve control of common vetch at Prosser in either year. Final dry weight of weeds in snap beans was not affected by cover crop kill method. Cover crop residues reduced weed biomass at snap bean harvest 0 to 89% at Prosser and 32 to 91% at Urbana compared to no cover crop controls. Cereal rye or a rye plus vetch mix suppressed weeds more consistently and completely than vetch alone. No-till planting snap beans into rolled and crimped cover crop residues often resulted in lower stands, delayed flowering, and reduced snap bean yield.



CONTROL OF PERENNIAL AND PERSISTENT WEEDS IN OLD BLUEBERRY PLANTINGS. R. V. Tocco Jr.*, B. H. Zandstra, C. M. Herrmann; Michigan State University, East Lansing, MI (146)

ABSTRACT

High bush blueberry plantings are often maintained for 40-50 years and effective weed control is important. Use of herbicides with the same mode of action over many years has led to major weed problems. Poison ivy, Virginia creeper, and wild grape are common climbing vine weeds. Horseweed, common pokeweed, goldenrod, yellow nutsedge, quackgrass, orchardgrass, and annual bluegrass are also prevalent problems. Diuron, simazine, hexazinone, and terbacil have been used for their efficacy and low cost in residual weed control. Glyphosate is used for emerged annual and perennial weeds. Hexazinone and glyphosate may cause blueberry injury if they contact young canes, and hexazinone may injure bushes on light soils with a high water table. Herbicides with new formulations and additional modes of action are needed to expand the weed control spectrum and allow for application during the growing season. 

   Experiments were conducted in commercial blueberry fields in Glenn, Michigan in 2008, 2009, and 2010 to compare new and registered herbicides for use on blueberry and to obtain data to support registration. Herbicides were applied in fall or spring, and alone or in combinations with postemergence herbicides. Flumioxazin at 0.429 kg/ha plus glyphosate at 0.482 kg/ha applied in the fall controlled most annual and perennial weeds into July. Flumioxazin applied alone did not give sufficient control of horseweed or common pokeweed. Mesotrione at 0.211 kg/ha suppressed most annual broadleaves but had no effect on grasses. It was more effective in combination with simazine 4.48 kg/ha or diuron 1.79 kg/ha. It appeared to be more effective if applied in early spring. Quackgrass, orchardgrass, and yellow nutsedge were sufficiently controlled by terbacil at 1.79 kg/ha. Terbacil in the new formulation, 80 WDG, was as effective as terbacil 80 WP. Halosulfuron at 0.053 kg/ha improved broadleaf control when applied in early spring in combinations with oryzalin 4.48 kg/ha, diuron 3.36 kg/ha, or simazine 4.48 kg/ha. It was more effective for broadleaf control when applied postemergence in June. Indaziflam at 0.073 kg/ha suppressed most annual weeds for 8-12 weeks. It was weak on horseweed, smartweeds, and had little effect on established perennials such as common pokeweed.    None of the treatments caused visible injury to blueberry when applied correctly. If residual herbicides are rotated and applied with foliar active herbicides, it should be possible to control most annual and perennial weeds in blueberry.



FIELD EVALUATIONS OF HERBICIDES FOR BOHEMIAN KNOTWEED (POLYGONUM X BOHEMICUM) CONTROL. K. Patten1, C. Metzger2, V. F. Peterson*3; 1WSU, Long Beach, WA, 2Washington State Univerisity, Long Beach, WA, 3Dow AgroSciences, Mulino, OR (147)

ABSTRACT

Although millions of dollars are spent annually on the chemical control of knotweed on public and private lands in the PNW, there have been few systematic assessments of the comparative efficacies of herbicides or herbicide timings for knotweed control. Replicated field trials with Bohemian knotweed (Polygonum X bohemicum) (BKW) were conducted from 2005 through 2009 near Naselle WA to compare herbicide efficacy on BKW with a full-size mature summer canopy (> 3 m) and during the spring growth flush when canopy stature is < 2 m.

 For trials on full-stature canopies, the herbicides imazapyr, imazamox, penoxsulam, glyphosate, triclopyr and aminopyralid and various combinations were applied from late May to August and efficacy was assessed 1 and 2 years after treatment (YAT). For trials on shorter-developing canopies, the herbicides imazapyr, glyphosate, triclopyr and aminopyralid were applied from mid-April to mid-May and regrowth was assessed 3 and 16 months after treatment (MAT). Additional treatments in later studies included same-year combinations of spring aminopyralid and mid-summer imazapyr for control of regrowth.  For treatment of full-size plants, the most consistent control 2 YAT was obtained with imazapyr (1.6 kg ae/ha) (46 to 99%), while control with glyphosate (9 to 22 kg ae/ha) was variable between studies (21 to 99%). Imazamox (0.56 kg ae/ha), penoxsulam (0.1 kg ae/ha) and triclopyr (3.6 kg ae/ha) provided no long-term control. Combinations of imazapyr (0.8 to 1.6 kg ae/ha) with glyphosate (6.6 to 13.2 kg ae/ha) or aminopyralid (0.25 kg ae/ha) did not improve control over imazapyr (1.6 kg ae/ha) alone.

For canopy treatment of spring growth across 6 trials, no herbicide was effective in providing consistent control (>60%) 2 YAT. Early timing of glyphosate (13 kg ae/ha), imazapyr (1.6 kg ae/ha) and triclopyr (4.8 kg ae/ha) provided 25 to 82% control 1 YAT, but by 2 YAT control was only 2 to 44%. Early timing of aminopyralid (0.125 to 0.25 kg ae/ha) provided 1 and 2 YAT control ranging from 2 to 98% and 0 to 87% respectively.  Short and long-term efficacy of aminopyralid was dependent on rate, timing, plant size and stand density at application and spray volume. Most consistent efficacy with aminopyralid was achieved at 0.25 kg ae/ha rate with spray volume ≥ 1130 l/ha,  targeting plants where all shoots had emerged and shoot height was 1-2.5 m.  An early season aminopyralid application to suppress canopy growth, followed by a mid-season imazapyr treatment, provided > 90% control 1 YAT.  For large stand of BKW a spring aminopyralid  application in ~4 m wide strips, spaced every ~10-12 m was found to be a cost-effective for creating easily  access spray paths & zones for subsequent summer application of imazapyr. 

 




EXAMINING THE UNPREDICTABLE NATURE OF YELLOW TOADFLAX IN COLORADO. N. J. Krick*; Colorado State University, Fort Collins, CO (148)

ABSTRACT

Yellow toadflax (Linaria vulgaris Mill.) is an exotic perennial forb that  is a serious weed in the Intermountain West and its range is expanding.  It is a difficult plant to control and site to site variation has been dramatic.  Identical herbicide efficacy trials were conducted at 5 geographically separated field sites in Colorado.  Chlorsulfuron and imazapyr were each applied at 4 rates and treatments were rated 1 and 2 years after treatment.  To support the field trials, a common garden study was conducted with germplasm harvested from the separate field sites.  Visual control and biomass, from the field sites, were analyzed 2 YAT.  Chlorsulfuron applied at 80 g ai/ha controlled > 95% of yellow toadflax at 2 sites and < 83% at 3 sites.  Imazapyr applied at 426 g ai/ha controlled > 93% of yellow toadflax at 3 sites and < 71% at 2 sites.  Field treatments reduced biomass of yellow toadflax by > 60% at 2 sites and < 45% at 3 sites.  There was a strong negative correlation (R=-0.9) between percent of shoots flowering and herbicide effectiveness; fewer flowering shoots resulted in better control.  The common garden study revealed differences in biomass by site, indicating genetic differences.  One site produced 40% more biomass than all other sites, but this site was of the 2 most successfully controlled field sites. A better understanding of the source of variation has been determined by this research and results provide more acceptable recommendations for long term control of yellow toadflax.



ABSORPTION AND TRANSLOCATION OF FLURIDONE, PENOXSULAM, AND TRICLOPYR BY EURASIAN WATERMILFOIL AND HYDRILLA. J. D. Vassios*1, S. J. Nissen1, T. J. Koschnick2; 1Colorado State University, Fort Collins, CO, 2SePRO Corporation, Carmel, IN (149)

ABSTRACT

The invasive species Eurasian watermilfoil (Myriophyllum spicatum) (EWM) and hydrilla (Hydrilla verticillata) are submersed species that are found across much of the United States.  Both of these species are perennial, but exhibit an annual growth habit, forming dense mats that can impact water quality.  An ongoing series of experiments have been examining herbicide absorption and translocation in these species using radiolabeled herbicides.  Herbicides evaluated include fluridone, penoxsulam, and triclopyr.  For the first experiments, translocation to the roots was examined following herbicide exposure in the water column.  Plants were treated with 10 ppb fluridone, 10 ppb penoxsulam, or 1 ppm triclopyr plus radiolabeled herbicide.  Plants were then harvested over a 192-hour time course.  Experiments were also conducted to examine translocation to shoots following root exposure to the same three herbicides.  Plants each received 200,000 dpm of radiolabeled herbicide, and were harvested over a 192-hour time course.  Upon completion of all experiments, plants were harvested, dried, oxidized, and radioactivity quantified using liquid scintillation spectroscopy.  Overall, herbicide absorption by EWM was two to four times greater than hydrilla. Shoot to root translocation of all herbicides was relatively limited with 97% and 87% or greater remaining in the shoots for EWM and hydrilla, respectively. For both species, triclopyr showed the greatest absorption over the 192-hour time course.  Following root exposure, fluridone absorption was greatest, but translocation to shoots was greater for penoxsulam and triclopyr (approximately 20%).




IMPACT OF HERBICIDE COMBINATIONS ON NON-TARGET AND INVASIVE SUBMERSED AQUATIC PLANTS. C. R. Mudge*1, L. M. Glomski2; 1US Army Engineer Research and Development Center, Vicksburg, MS, 2US Army Engineer Research and Development Center, Lewisville, TX (150)

ABSTRACT

Herbicides have been used effectively for several decades to manage and control noxious and invasive aquatic weeds.  In the past seven years, six herbicides have received FIFRA-Section 3 registration or experimental use permits (EUP) for aquatic use.  Some of these herbicides, including acetolactate synthase inhibitors bispyribac-sodium, imazamox, and penoxsulam as well as the protoporphyrinogen oxidase inhibitor flumioxazin are efficacious against hydrilla (Hydrilla verticillata).  Although most aquatic herbicides have traditionally been applied as stand-alone treatments, combinations of diquat + copper and diquat + endothall have proven effective when combining herbicides with different modes of action.  Less than desirable initial results and concerns of herbicide resistance with these newer enzyme specific herbicides have led to research efforts to evaluate combinations of recently registered and established aquatic herbicides.  A series of experiments were conducted at the US Army Engineer Research and Development Center in Vicksburg, MS, to evaluate low dose combinations of bispyribac-sodium (B, 10 µg active ingredient (a.i.) L-1), diquat (D, 100 µg a.i. L-1), endothall (E, 500 and 750 µg acid equivalent (a.e.) L-1), flumioxazin (F, 50 µg a.i. L-1), imazamox (I, 50 µg L-1), or penoxsulam (P, 5 µg L-1) against hydrilla.  Herbicide exposures were static, 8 hr, 72 hr, 24 hr, 7 d, and static for bispyribac-sodium, diquat, endothall, flumioxazin, imazamox, and penoxsulam alone and combination treatments.  These trials were conducted to determine if combination treatments would improve control of hydrilla compared to these herbicides applied alone at low rates.  In addition, these combinations were evaluated against the non-target submersed aquatic plants American pondweed (Potamogeton nodosus), coontail (Ceratophyllum demersum), Illinois pondweed (Potamogeton illinoensis), and two biotypes of vallisneria (Vallisneria americana), narrow and wide-leaf.  Hydrilla shoot weight was reduced 48 to 95% with B10, D100, and E500 compared to the nontreated control, whereas E750, F50, I50, and P5 applied alone failed to reduce shoot dry weight at 9 WAT.  Although many combinations of bispyribac-sodium, diquat, and endothall plus other herbicides were efficacious against hydrilla, no additional control was provided compared to these products alone.  Flumioxazin, imazamox, and penoxsulam when used in combination with each other failed to reduce plant hydrilla biomass.  The non-target submersed aquatic plants were also affected by individual herbicides and combinations.  Herbicide treatments including E500, B10 + D100, B10 + E500, E500 + F50, E500 + I50, and E500 + P5 provided 47 to 83% shoot biomass reduction of narrow-leaf biotypes of vallisneria.  Wide-leaf vallisneria shoots were affected by the herbicide treatments E500, E500 + F50, and E500 + I50.  All herbicide treatments, except B10 and P5, reduced coontail shoot dry weight compared to the non-treated control.  American pondweed shoot biomass was reduced by all herbicide treatments except B10, F50, and P5.  Flumioxazin was the only individual or combination treatment not significantly different from the control when applied to Illinois pondweed.  The concentrations evaluated are approximately 12.5 to 50% of the current recommended use rates.  Consequently, less than desirable results were attained with some of the individual and combination treatments when applied to hydrilla.  Overall, these results indicate low concentration combinations of several registered herbicides and bispyribac (EUP) may be effective in controlling hydrilla.  However, further evaluation of higher concentrations of those combinations evaluated in these studies along with evaluation of other herbicide combinations in laboratory and mesocosm trials will be necessary.  In addition, the potential for increased target plant control using herbicide combination must be balanced with potential negative impacts on non-target plants.




RAPID RESPONSE: PUTTING EARLY DETECTION & RAPID RESPONSE INTO PRACTICE. A. V. Tasker*; USDA, APHIS, Plant Protection & Quarantine, Riverdale, MD (151)

ABSTRACT

Early Detection & Rapid Response implementation continues. <span style=\"\" color: \" windowtext\\?>The Federal Interagency Committee for the management of Noxious and Exotic Weeds issued in 2003 a conceptual design for an Early Detection and Rapid Response (EDRR) system for invasive plants. This was the culmination of a stakeholder process initiated in 1998. The design identified gaps in existing response programs and proposed a template for a U.S. national system to detect, assess, and respond to invasive species infestations in their early stages of establishment. One of the main EDRR objectives is to encourage management groups to promote EDRR as a preferred management option for new and emerging invasive species, and to assume a role in the development of a National EDRR System for Invasive Plants. Currently, attempts are underway to foster a regional approach to EDRR to connect local efforts to national regulatory and non-regulatory coordination groups.




NEW FEDERAL WEED RISK ASSESSMENT GUIDELINES IN ACTION: EXAMPLES FOR THREE SPECIES. B. P. Caton*1, A. Koop2, L. Fowler2, L. Newton2; 1USDA-APHIS-PPQ-CPHST, Raleigh, NC, 2USDA, Raleigh, NC (152)

ABSTRACT




GUIDELINES FOR THE MOLECULAR IDENTIFICATION OF INVASIVE PLANTS. S. M. Talley*1, L. J. Cseke2; 1USDA, Fort Collins, CO, 2UAHuntsville, Huntsville, AL (153)

ABSTRACT

The primary goal of these guidelines is to provide direction for the development of cost-effective and reliable plant diagnostic tools to identify plants or plant tissue that cannot be identified through visual means in order to accurately distinguish prohibited plants and plant materials at U.S. ports and in the field. Plant identification through molecular diagnostics technologies is critical to support PPQ’s safeguarding goals to protect our plant resources against the unplanned and accidental introduction of invasive plant species and other prohibited plant taxa that are carriers of plant pests and disease. In these guidelines, we detail strategies, pitfalls, and case studies that provide the most up-to-date, accurate, reproducible, and cost-effective molecular methodologies to identity plants. Some strategies that are covered include what methods are best to provide the most reliable and cost-effective results; which nuclear and plastid DNA regions are best for fingerprinting and what are their limitations; how does one mine nucleotide databases and the literature for quality sequences; which plant tissues are best for DNA extraction; how does one avoid DNA contamination; and how to analyze the sequences derived from PCR products. Also included in these guidelines are cost-saving modifications for when large numbers of specimens require molecular approaches for high-throughput identification.

 




DETECTION OF SIGNIFICANT INFESTATION OF GOATSRUE IN MCKEAN COUNTY PENNSYLVANIA. M. Bravo*, J. Zoschg; Pennsylvania Department of Agriculture, Harrisburg, PA (154)

ABSTRACT

Goatsrue (Galega officinalis) is a federally listed noxious weed with a limited distribution. In 1891 goatsrue was introduced to Utah by the Utah Agricultural Experimental Station where it was tested as a livestock forage and green manure crop. Only after its establishment was its poisonous and highly invasive attributes discovered. By 1981, 60 square miles of cropland, irrigation waterways, pastures, roadways and wet marshy areas in Cache County, Utah were infested. In 1981 the United State Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) targeted goatsrue for eradication. A herbarium search found specimens from 1890 to 1960 in 10 continental states and Washington D.C.
Goatsrue was first documented in PA in the 1950’s at the Morris Arboretum in Montgomery County. It was added to the PA Noxious Weed Control Law list in 2000 after a USDA/CAPS survey detected additional sites in the state. Prior to 2009, only 6 viable and under ‘official control’ populations had been detected. However, noxious weed surveys conducted in August of 2009 by local, state and federal field staff discovered multiple sites of flowering goatsrue adjacent too or infesting cropland throughout 22% of the 900 square miles of McKean County. This significant discovery prompted an early detection rapid response control effort by the PA Department of Agriculture, PA Department of Transportation, Keating Township and Smethport Boro officials to immediately implement measures to prevent further maturation of seedpods. Noxious weed control orders were issued to limit the transport and sale of aggregate infested with goatsrue seed and all known infestations were chemically or mechanically treated. During the winter of 2010, PDA and partners developed outreach materials and work plans to assist landowners with control of this state and federal noxious weed.

PDA has documented 50 acres of goatsrue on 139 properties as of September 2010. Populations were surveyed, measured and treated (chemical, mowing). Emergence of the seedbank and regrowth in mowed populations occurred at all locations and treatments were repeated. The data from herbicide trials (2006-2010) has shown that Garlon 3A, Milestone, Vista, Oust, Arsenal, Banvel and glyphosate alone or in combination - applied March through September; are appropriate herbicides to use in Pennsylvania for perennial goatsrue control. Herbicide selection is based on site location. For glyphosate-efficacy is dependent on stage of growth. The application of Oust with the post emergence treatments suppressed seedbank emergence for 5 months. In all, 95% or more of the populations were prevented from producing viable seed.

 

In summary, extensive surveys have determined that the McKean County infestation is directly related to the movement of contaminated soil from the dredging of Lake Hamlin in the past five years. Municipalities, private businesses and private landowners used the dredgings as fill material for driveways and other projects. This has lead too the direct infestation of hayfields, drainage ditches, flowerbeds, landscape areas, commercial aggregate material and vacant lots throughout the region. Property descriptions range from roadside ditches in the Alleghany National Forest, Elk County and Elk State Forest, Cameron County; to State, Township and Boro maintained roads in Cameron, Potter and McKean County; to 4 commercial stockyards (stone, sand, sawdust, bark mulch) and multiple hayfields, fallow meadows and riparian areas along two waterways in the vicinity of Smethport. All private, local, state and federal landowners are committed to continued seedbank suppression in the future.  

 




EFFECTS OF IRRIGATION WITH RECLAIMED WASTEWATER ON THE EFFICACY AND FATE OF ALS INHIBITORS IN SOIL. G. Dvorkin, B. Rubin*, B. Chefetz; Hebrew University of Jerusalem, Rehovot, Israel (155)

ABSTRACT

In semi-arid countries including Israel, water is a limited resource and therefore there is an increased demand for reclaimed wastewater (RWW) for crop irrigation. RWW contains dissolved salts, organic matter and suspended materials that might interact with the herbicides thus reducing their activity. RWW also contains high levels of microorganisms which might affect the herbicides activity in soil. In recent years farmers have reported a significant reduction in herbicide efficacy in cotton fields that have a long history of irrigation with RWW. We hypothesized that irrigation with RWW affects the microbial activity in the soil and therefore might increases the biodegradation of the applied herbicides. Alternatively, we proposed that the high load of dissolved organic matter (DOM) in the irrigated soil may affect the adsorption and mobility of herbicides hence, reducing their efficacy. Results of three field experiments showed that the activity of some ALS-inhibiting herbicides (particularly that of trifloxysulfuron) has declined faster then others resulting in high weed infestation. The level of the herbicides in the soil was estimated using a soil bioassay with Sorghum bicolor as a test plant. Shoot growth inhibition caused by trifloxysulfuron declined in RWW–irrigated soil so that 20 days after application (DAA) there was no significant difference in plant shoot growth between soil containing ALS inhibitor (trifloxysulfuron or iodosulfuron) and the control. Greenhouse experiments conducted with trifloxysulfuron confirmed that herbicide activity in the soil is significantly reduced by the irrigation with RWW compared to soil irrigated with fresh water. Experiments conducted with sterilized and non-sterilized RWW irrigated soil suggested that microorganisms play major role in ALS inhibitors loss of activity in soil irrigated with RWW.




ENHANCED ATRAZINE DEGRADATION: DEGRADERS NUMBERS AND ACTIVITY FOUR YEARS AFTER LAST S-TRIAZINE APPLICATION. L. Krutz*, R. M. Zablotowicz, K. N. Reddy; USDA-ARS, Stoneville, MS (156)

ABSTRACT

The longevity of enhanced s-triazine degradation in agricultural soils may vary depending on crop and s-triazine application frequency.  A field study was conducted on an s-triazine adapted soil to determine the effect of crop (continuous corn or continuous soybean), soil (bulk or rhizosphere), and time since last s-triazine application (1, 2, 3, or 4 yrs) on atrazine degrader numbers and activity.   Atrazine degrader numbers were initially higher in soybean (14,000 cells g-1 soil) than corn (9,000 cells g-1 soil) but declined more rapidly in the former.  Additionally, degrader numbers pooled over crop were initially higher in rhizosphere (15,000 cells g-1) than bulk soil (8,000 cells g-1 soil) but declined more rapidly in the latter.  Pooled over crop and soil, cumulative 14CO2 evolution from ring-labeled 14C-atrazine 35 d after application declined over time: 78.6% 1 yr post s-triazine application, 75.7% 2 yr post s-triazine application, 67.4% 3 yrs post s-triazine application, and 64.0 % 4 yrs post s-triazine application.  Yet, after not received an s-triazine application for at least 4-years, cumulative atrazine mineralization was still 6-fold higher in adapted than non-adapted soil.  Our results indicate that omitting s-triazine applications can reduce degrader numbers in s-triazine adapted soils, but more than four years is required to bring mineralization kinetics back to non-adapted levels, regardless of crop.   




CONTRIBUTIONS OF AGRONOMIC PRACTICES, PRECIPITATION PATTERNS, AND LANDSCAPE VULNERABILITY TO ATRAZINE LOAD IN THE BIG BLUE RIVER BASIN. K. Dhakal*1, M. L. Bernards1, M. Milner1, P. L. Barnes2, P. J. Shea1; 1University of Nebraska-Lincoln, Lincoln, NE, 2Kansas State University, Manhattan, KS (157)

ABSTRACT

Atrazine concentrations in the Big Blue River Basin in Nebraska and Kansas periodically exceed the EPA Total Maximum Daily Load (TMDL) of 3 mg L-1. We assessed the impact of planting dates, rainfall and antecedent soil water content on stream-measured atrazine in the basin from 1997 through 2004.  Atrazine load was monitored weekly at several sampling stations. Daily crop-planted acres by date and county were obtained from the USDA Risk Management Agency (RMA) and serially complete precipitation data sets were obtained from the High Plains Regional Climate Center (Lincoln, NE). Assuming sampling locations as drainage points, unique upstream areas (UUAs) were delineated from a digital elevation model. The percentage of crop-planted area by date for each UUA was calculated from RMA data. Soil moisture was estimated using Hybrid-Maize, a simulation model for corn growth and yield. Maximum atrazine loading occurred between mid-May and early June, immediately following multiple rainfall events that saturated the soil profile and caused runoff from agricultural fields. Major atrazine loadings in the UUAs followed major precipitation events, which generally occurred after most of the corn had been planted but during sorghum planting.  A heuristic analysis was conducted from day 110 when 10% corn was planted to day 170 when 90% of the sorghum was planted.  Results from the independent UUAs imply that atrazine loadings are related to rainfall patterns each year. When data from all independent UUAs were pooled there were significant effects of rainfall, soil moisture, corn planting progress, and sorghum planting progress. Results provide decision support to farmers, agencies, extension workers, and scientists for conservation management and restoration of impaired watersheds in agricultural settings.




REDUCTIONS IN RUNOFF OF CHLOROTRIAZINE HERBICIDES TO SURFACE WATER DUE TO ADOPTION OF BEST MANAGEMENT PRACTICES. R. S. Fawcett*; Fawcett Consulting, Huxley, IA (158)

ABSTRACT

Concentrations of the chlorotriazine herbicide, atrazine, have declined in U.S. surface water during a period when widespread usage continued.  The annual mean atrazine concentrations in Rathbun Lake in Iowa declined by 85% from 1996 to 2009.  The U.S. Geological Survey measured a 61% decline in atrazine concentrations in Midwestern rivers from 1989 to 1998.  Atrazine concentrations in untreated water from 103 community water systems utilizing surface water declined significantly from 1994 to 2006.  This improvement in water quality is due, at least in part, to the adoption of best management practices (BMPs) by growers who value and use atrazine as a foundation for weed control in corn and sorghum.  BMPs effective in reducing runoff of herbicides into surface water include but are not limited to conservation tillage, buffers and vegetated filter strips, constructed wetlands, terraces, contour planting, postemergence application, application timing, drainage improvement, and mechanical incorporation.  The U.S. Department of Agriculture Natural Resources Conservation Service concluded that current adoption of soil conservation practices alone has resulted in a 51% reduction in atrazine loads in the Mississippi River.  Efficacy of BMPs has often depended on site conditions.  Soil type and structure, topography, and antecedent soil moisture have all influenced the efficiency of BMPs.  Published natural rainfall runoff studies over 9 site-years of data reported an average 75% reduction in runoff of atrazine and simazine with no-till compared to moldboard plowed plots.  In 18 filter strip studies, retention of atrazine averaged 68%.  In 8 studies, reductions in runoff of atrazine with mechanical incorporation into the soil averaged 51%.  Use of BMPs has dramatically reduced atrazine concentrations in surface water while continued use of atrazine has allowed economic benefits through improved weed control and environmental benefits through facilitation of conservation tillage.



MUSINGS OF A WEED SCIENCE GRANT WRITER. C. L. Brommer*; BASF, Raleigh, NC (159)

ABSTRACT

Grants, aid, and other financial support can be the life blood of weed science research. This is true for weed science educators, extension, and advocates. In short, funding will take ideas and innovation to action. Something which is vital to weed science can be difficult to source. 

Both new and experienced weed scientists can struggle to fund their ideas. This can be particularly true for new weed scientists. Funding can come from many sources, both public and private. Through surveys conducted by weed scientists, it was determined that the amount of funding which comes from private sources, industry in particular, is the largest source of weed science funding. 

Connections to industry can be difficult to forge for new faculty members or recent college graduates in weed science. There are many difficulties in seeking out funding from federal, state, and commodities groups. There can be difficult to understand application forms, adjusting your ideas to meet the application forum established by these funding organizations is no easy task for the grant writer.

There are ways to assist scientists in successful mechanisms of being awarded grant/aid. WSSA contains members with a wealth of experience in the acquisition of grant/aid. These experienced grant writers and funding seekers have built a knowledge base through countless interactions with grant stakeholders and funding outlets. These members have developed techniques to approach the craft of acquiring funding. Dr. David Shaw is one of these WSSA members. His career story is a journey from a junior faculty member at Mississippi State University, to NASA, and now as the MSU Vice President for Research and Economic Development. Selected commentary and shared response to his story will be available on WWW.WSSA.net.




THE INDUSTRY PERSPECTIVE ON GRANTS AND AID. D. Refsell*; Valent, U.S.A. Co., Lathrop, MO (160)

ABSTRACT

   Industry, chemical companies and other providers of crop production infrastructure are a strong force for funding weed science research. Herbicides, herbicide tolerant crops, additives to sprayer solutions, adjuvant, plant growth regulators, plant protection machines or chemicals are a multi-billion USD$ world wide businesses. Many farmers could not continue to produce the amount of food, fiber, and bio-fuel without the help of crop protection chemicals.

This large industry has, historically, worked closely with students, faculty, and state/federal employees to develop crop production solutions. 

But, what drives the private industry research goals? Why do some weed scientists have more funding from industry than others? Perhaps the best question is, “How can weed scientists work with industry for the betterment of their constituents and for grant/aid?” This multi-billion $ industry has been a major driver of research at public institutions, funding faculty, students, and similar stakeholders.

The panel of weed science industry members will answer the aforementioned questions as well as those from the symposium’s virtual mailbox, the audience, and moderator. The panel will also focus on the different myths surrounding industry funding of public or private researchers. This group will also develop a best practices statement to help new weed scientist understand the expectations of industry when they fund research. Selected commentary and shared response to this round table will be available on WWW.WSSA.net.




ETHICAL CONCERNS WHEN YOU ACCEPT FUNDING. C. L. Brommer*; BASF, Raleigh, NC (161)

ABSTRACT

Ethics is defined by Merriam-Webster as “a set of moral principles: a theory or system of moral values.” An expansion on this definition can be:  "Ethics is a practice used to examine the decisions humans make, focusing on the critical analysis of how the concepts of “right” and “wrong” impact human choices." Morals, by contrast, can be thought of the actions taken in a decision system where as ethics is a focus on the rationale behind the decisions which are made. The WSSA continues to work to educate its membership in the field of ethics.

What are the ethical concerns of accepting funding or other items from a group to conduct research, teaching, extension, or other professional practice? What are the ethical obligations of a researcher when accepting funding from a public source?   

There are ethical questions raised from accepting funding from a private source, companies in particular, who are for-profit entities. The research data collected from a privately funded course can be used to influence stakeholders. The data collected could also become a fulcrum to leverage continued funding from private groups. The question of the quality of data which comes from privately funded research or even the validity of the data is not uncommon.

There is something of a paradox for weed science researchers. There is a large amount of grant/aid which comes from private sources. Many research programs could not function without the influx of private funding. Is there a mechanism by which the researcher can retain their ethics while conducting this research for hire? What obligations do the researchers have to not place the private funding source in a position where the private sources ethics are not compromised?

This session will present a basic outline of research ethics with statements from private and public resources in weed science. The conversation concerning the ethics of private funding will begin in this session and continue at WWW.WSSA.net with correspondence from the session, online resources, and a FAQ for basic ethical questions in weed science research grant/aid.

 




WEB GEMS. 21ST CENTURY STEPS TO SEEK OUT FUNDING IN WEED SCIENCE. C. L. Brommer*; BASF, Raleigh, NC (162)

ABSTRACT

The seeking of funding, grants, aid, or financial compensation is an important process for any scientist or educator. The world wide web has made the availability of information for grant seekers available. The participants will go through the process of seeking out funding using different search techniques. The step-wise process for seeking funding knowledge on the internet will be explored. 

Consolidator sites will be highlighted; these sites contain links and information on available grants, aid, or funding from non-profit or for-profit sources. There is a premium on contact information for different people with access to projects or funding related to weed science. The web gems web page will showcase the varied sites on the internet which hold information on grants, aid, gifts, and funding for weed scientists. There is a wealth of information consolidated in online zones for seeking out funding, many sponsored by other science societies. The WSSA.net site will redirect the user to these consolidator sites as well as having a unique set of links and information dealing with grants/aid, ethics of aid, ideas from season grant/aid weed scientists, and other topics related to keeping your weed science ideas well funded.




"ASK THE ELDERS" A ROUND TABLE OF WEED SCIENTISTS ON BOTH SIDES OF THE GRANT AND AID PROCESS. C. L. Brommer*; BASF, Raleigh, NC (163)

ABSTRACT

         "Experience keeps a dear school, yet fools learn in no other", a quote from Benjamin Franklin (Poor Richard’s Almanac, Nov. 1743). This session is designed to “keep a dear school” and not be a fool by seeking funding without some advice from some esteemed members of the WSSA.   Both recent and seasoned weed scientists can benefit from the experiences of successful grant writers and the well funded scientists of the WSSA.

The panel members’ discussion will focus on their unique experiences in seeking funding from private and public sources. Panelists will share their perspectives on best management practices for acquiring funding. Worst practices will also be discussed as a means to help the participants define a pathway for seeking out funding in weed science by not repeating mistakes of other WSSA members. Ethics, legal issues, management of grant funding, sources of funding, and peer to peer interactions will be part of this session.

Participants in the session will drive questions, answers to questions and selected commentary will be available at WWW.WSSA.net. Social media will also be used to engage participants who are not in the session. Anonymous submission of questions will be utilized to foster a vibrant discussion. The opportunity exists to have future questions answered by the panelists or other WSSA funding experts.




GROUP DRIVEN GRANT AND AID SESSION. HOW TO LEAVE WSSA 2011 READY TO WRITE OR ACQUIRE A GRANT OR AID. C. L. Brommer*; BASF, Raleigh, NC (164)

ABSTRACT

The next steps, utilizing our collective knowledge of funding opportunities to drive successful grant/aid outcomes for the WSSA membership.

At the conclusion of the symposium on “Navigating the Universe of Grants, Contracts, and Gifts in the 21st Century,” participants will conduct a end of task assessment of the symposium. This assessment will include positive aspects of the symposium, negative components of the symposium, suggestions for improvement, and future work to share concerning the search for funding.

Some participants will be interacting remotely; using social media and streaming technologies to engage with the group. Additional emphasis will be placed on developing mentors for grant/aid seeking, online materials for finding aid opportunities, issues of legal, ethical, or moral significance concerning weed science grants/aid. Social media will be used to share the outcomes from this session as well as WWW. WSSA.net 




INTRODUCTION TO THE SYMPOSIUM: HISTORY OF SULFONYLUREA HERBICIDES IN TURFGRASS ENVIRONMENTS. P. C. Bhowmik*; University of Massachusetts, Amherst, MA (165)

ABSTRACT

Weed management is a science-based decision-making process that includes the knowledge of weed biology, environmental information, and available technology to maintain qualities of turfgrass species. This type of approach may lead to least possible risks to people and the environment. Although sulfonylurea (SU) herbicides were initially introduced in the agricultural market in 1982, the researchers evaluated SUs for control of weedy and overseeded grasses. Later, SUs were evaluated for selective control of broadleaf weeds, sedges, and kyllinga species in both cool-season and warm-season turfgrasses. Herbicidal activity of SUs is characterized by high biological activity on susceptible weeds, short half-lives and low toxicities to animal species. SUs act by inhibiting the plant-specific ALS enzyme, which is required for the biosynthesis of branched-chain amino acids (valine, leucine and isoleucine) required components of the growth processes of cell division at the root and shoot tips. In 1990’s, chlorsulfuron and metsulfuron were introduced into the turfgrass market for selective control of broadleaf weeds and difficult-to-control grasses, including wild garlic (Allium vineale), prostrate spurge (Euphorbia maculata) and bahiagrass (Paspalum notatum). In 2000’s, halosulfuron, rimsulfuron, flazasulfuron, sulfometuron, sulfosulfuron, foramsulfuron and trifloxysulfuron were introduced for controlling problematic weeds like annual bluegrass (Poa annua), clumpy ryegrass (Lolium perenne), creeping bentgrass (Agrostis palustris), and sedges like yellow nutsedge (Cyperus esculentus), purple nutsedge (Cyprus rotundus), green kyllinga (Kyllinga brevifolia) and false green kyllinga (Kyllinga gracillima). In this symposium, speakers will examine the current status of SUs and identify potential benefits and drawbacks in using these herbicides for weed management practices. Speakers will discuss their research findings, vision, and possible recommendations in relation to the safety of turfgrass (established and overseeding stands), environmental concerns (persistence and lateral movement) and potential evolution of weed resistance. Successful cases of weed management practices in both cool-season and warm-season turfgrass systems will be highlighted.




BEHAVIOR OF SULFONYLUREA HERBICIDES IN PLANTS: MODE-OF-ACTION, UPTAKE, TRANSLOCATION AND METABOLISM. J. S. Claus*, C. A. Silcox, H. M. Brown; DuPont Crop Protection, Wilmington, DE (166)

ABSTRACT

Behavior of Sulfonylurea Herbicides in Plants: Mode-of-Action, Uptake, Translocation and Metabolism. J. S. Claus, C. A. Silcox, H. M. Brown, DuPont Crop Protection, Wilmington, DE

 

Sulfonylurea’s (SU’s) represent one of the largest classes of herbicides with about 30 registered actives world wide. This innovative class of chemistry revolutionized the crop protection industry by providing growers with outstanding weed control at very low use rates. Sulfonylurea herbicides are registered in a large number of broadleaf and grass crops as well as in non-crop and turf.  SU herbicides also have an excellent environmental profile, do to their low use rates, that is still considered an industry standard today. The first SU herbicide was synthesized by DuPont chemist Dr. George Levitt in 1975 and the first commercial products were launched with chorsulfuron and sulfometuron methyl in 1982. 

 

Sulfonylurea herbicides are very effective inhibitors of plant cell division; they inhibit acetolactate synthase (ALS) a key enzyme in the pathway of branched chain amino acids, leucine, isoleucine and valine in plants.  Other cellular processes such as protein synthesis, photosynthesis and respiration are not inhibited directly by SU’s.  The rapid inhibition of cell division stops growth within minutes after application at the growing tips of both roots and shoots of susceptible plants. Mature tissue and cells are not affected for some time after application giving the appearance of very slow activity.

 

SU’s are rapidly absorbed by plants and translocated in both phloem and xylem to the active cell division sites.  For shoot uptake a non-ionic surfactant or crop oils containing 15 to 20% emulsifier improves uptake and control.  Both aid in moving the SU across the cuticle.  This is especially true when weeds get larger or environmental conditions enhance cuticle development. 

 

Uptake and translocation occurs in both sensitive and tolerant plants.  The relative sensitivity of the plant to SU’s is proportional to the metabolism rate.  In tolerant plants the half life is very short while sensitive plants have much longer metabolism.  Stress conditions that slow metabolism will increase phytotoxicity. Tolerant plants under stress will exhibit yellowing and short internodes until the stress is removed and metabolism degrades the SU herbicide.   Plant stress can come from many sources including but not limited to; insects, disease, soils, nutrients, heat, cold, moisture and other pesticides.




SULFONYLUREA HERBICIDES FATE IN SOIL: DISSIPATION MECHANISMS, MOBILITY, AND OTHER PROCESSES. T. L. Grey*1, P. E. McCullough2; 1University of Georgia, Tifton, GA, 2University of Georgia, Griffin, GA (167)

ABSTRACT

Sulfonylurea herbicides used in turf, chlorsulfuron, flazasulfuron, foramsulfuron, halosulfuron, metsulfuron, rimsulfuron, sulfometuron, sulfosulfuron, and trifloxysulfuron are all weak acids, with pKas ranging from 3.3 to 5.2.  They are all used at low rates ranging from 4 to 100 g/ha.  While these use rates put their soil activity in the parts per billion category, they still have residual activity with variable persistence. They are susceptible to limited amounts of soil leaching with weak adsorption to soil clay minerals.  Sulfonylurea herbicides used in turf have variable soil organic matter adsorption, which is soil type dependent.  The persistence and activity of these sulfonylureas is affected by soil pH.  At soil pH of 7.0 and greater, some of these sulfonylurea herbicides tend to persist for longer periods with half-lives extending into years rather than days.  In normal use patterns with pH of 7 and less, dissipation occurs via chemical hydrolysis and microbial degradation with half-lives ranging from days to months.  Overall, sulfonylurea herbicides adsorption is negatively affected by increased pH (increased persistence) and positively related to increased organic matter (decreased activity).  




MOVEMENT OF SULFONYLUREA HERBICIDES TO NONTARGET SITES. S. Askew*; Virginia Tech, Blacksburg, VA (168)

ABSTRACT

An increase in sulfonylurea registrations for use in turfgrass in the United States causes concern over the potential mobility of these herbicides in surface runoff and on equipment and foot traffic across treated turf. Herbicide tracking and lateral mobility are of particular concern to the golf industry where sensitive and tolerant turf species comprise adjoining areas on the golf course. Research at Virginia Tech has shown several sulfonylurea herbicides can be dislodged from treated turf and deposited on neighboring turf via foot traffic or equipment tires. Radioactive rimsulfuron persisted on annual bluegrass and perennial ryegrass foliage up to four days after application when 40% of applied herbicide was extracted with water. In field studies, post-treatment irrigation eliminated injury tracks on neighboring turf while irrigating tracked turf immediately after mower traffic had no effect. After these and other studies, several herbicide labels included a recommendation to irrigate treated turf to rinse chemical residues from the leaf surfaces prior to turf traffic.

 

Applications of flazasulfuron, trifloxysulfuron sodium, rimsulfuron, and pronamide made upslope from sensitive perennial ryegrass injured the turf after 2 to 6 cm of irrigation or rainfall within 4 hours of application. Trifloxysulfuron sodium injury was apparent 0.25 to 1 m below treated plots. Metsulfuron and rimsulfuron caused injury only 0.25 m below treated plots, while pronamide injured perennial ryegrass 2.5 to 4 m below treated plots. Flazasulfuron injured perennial ryegrass due to runoff similar to pronamide. Flazasulfuron drift was assessed using corn as a sentinel plant and herbicide deposition to corn was assessed using bioassays. At wind speeds of 6.4 to 9.7 km hr-1, Flazasulfuron did not drift beyond 4.6 m when applied through a Turbo TeeJet TTVP 11004 with pressure set to provide coarse to very coarse droplets as specified in the herbicide label. 

 

Sulfonylurea herbicide movement in turf is determined by herbicide rate, sensitivity of nontarget plants, and environmental factors such as wind, saturated soils, and dew that aid in drift, runoff, and tracking, respectively. To avoid lateral mobility of sulfonylurea herbicides, applicators may avoid treating areas upslope of sensitive grasses, avoid treating saturated soils or when rainfall is eminent, apply post-treatment irrigation after 4 to 12 hours to wash non-absorbed herbicide into soil, and avoid applying when wind speed is greater than 6.4 km hr-1 or with nozzles that produce fine droplets.

 




ROLE OF ADJUVANTS ON SULFONYLUREA HERBICIDE EFFICACY. D. Sanyal*1, P. C. Bhowmik2; 1Monsanto Company, St. Louis, MO, 2University of Massachusetts, Amherst, MA (169)

ABSTRACT

Sulfonylurea herbicides kill weeds by inhibiting acetolactate synthase, an enzyme required for cell growth. They work on a range of grasses and broadleaf weeds. Previous studies have been conducted to identify the proper adjuvant systems to obtain optimum activity of sulfonylurea herbicides. The impact of adjuvant varies among the weed species and growth stages. This presentation will review the effect of various adjuvants on sulfonylurea herbicide activity from published literature.




ENVIRONMENTAL AND SEASONAL EFFECTS ON EFFICACY AND COOL-SEASON TURFGRASS TOLERANCE TO ALS INHIBITING HERBICIDES. S. Hart*; Rutgers, The State University of New Jersey, New Brunswick, NJ (170)

ABSTRACT




USE OF SULFONYLUREA HERBICIDES FOR BROADLEAF WEED CONTROL IN WARM-SEASON TURFGRASS. B. J. Brecke*; University of Florida, Jay, FL (171)

ABSTRACT

There are many herbicides available for postemergence weed control in turfgrass. Until relatively recently, growth regulator type herbicides in the phenoxy family of herbicides and the benzoic herbicide dicamba applied alone or in various combinations accounted for most of the herbicides applied for postemergence broadleaf control in turfgrass. Several herbicides in the sulfonylurea family (SU) including chlorsulfuron, trifloxysulfuron, flazasulfuron, iodosulfuron, thifensulfuron, metsulfuron, rimsulfuron, and sulfosulfuron provide postemergence control of many broadleaf weeds. With the more recently registered products added to the list of older herbicides, there are several herbicide options available for postemergence broadleaf weed control in turfgrass. Warm-season turfgrass tolerance varies with the specific SU herbicide used. While bermudagrass and zoysiagrass tolerate most of the SU=s, the list available for use on St. Augustinegrass is more limited. A survey was conducted to determine the utility of SU herbicides indicated that Virginia buttonweed control is comparable between SU and non-SU treatments. Other broadleaf species that are controlled by two or more members of the SU family include common chickweed, white clover, dandelion, dichondra, henbit, knotweed, plantain and spotted spurge. Some SU labels call for the addition of a surfactant while others are used alone. More difficult to control broadleaf weeds often require multiple applications of SU’s at 3 to 6 wk intervals for effective control. It is imperative that SU’s be used in rotation with non-ALS inhibiting herbicides to prevent the development of SU-resistant weeds.




BROADLEAF WEED CONTROL WITH SULFONYLUREA HERBICIDES IN COOL-SEASON TURFGRASS. J. Derr*; Virginia Tech, Virginia Beach, VA (172)

ABSTRACT

Certain sulfonylurea herbicides are utilized for weed management in cool-season turfgrass, although there are fewer options compared to warm-season turfgrass species.  Although broadleaf weeds are generally controlled utilizing chemicals from the phenoxy, pyridine, and benzoic acid families, sulfonyurea herbicides do control certain dicots.    The growth regulator herbicides provide economical, broad spectrum control of annual and perennial broadleaf weeds.   Sulfonylurea herbicides, however, tend to have greater specificity among broadleaf plants and the number of dicot species controlled generally increases with increasing rate.  Sulfonylurea herbicides can be added to growth regulator herbicides for enhanced weed control or they can be used alone for controlling specific broadleaf weed species.  The primary sulfonylurea herbicides utilized in cool-season turf include chlorsulfuron, halosulfuron, metsulfuron, and sulfosulfuron.  The primary use of halosulfuron is for sedge control in a wide range of cool-season turf species, although it will provide preemergence and/or postemergence control of certain broadleaf weeds in the aster, mustard, and smartweed families.   A common use of sulfosulfuron is also sedge control.  In fine turf, use of sulfosulfuron and chlorsulfuron in cool-season grasses is limited to Kentucky bluegrass (Poa pratensis L.) and fine fescue (Festuca spp.) as they can control tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) at certain use rates.   Metsulfuron is also used primarily in Kentucky bluegrass and fine fescue.   Chlorsulfuron and metsulfuron can be used on tall fescue in rights of way and other unimproved turf areas, although at lower rates than for bluegrass species.   Chlorsulfuron, metsulfuron, and sulfosulfuron will control certain annual broadleaf weeds such as common chickweed (Stellaria media L.) and wild mustard (Sinapis arvensis L.) and they will suppress or control certain perennial broadleaf weeds such as dandelion (Taraxacum officinale G. H. Weber in Wiggers).  Little data exists, however, on the response of most broadleaf weeds to the sulfonylurea herbicides used in cool-season turfgrass.




COOL-SEASON GRASS REMOVAL FOR BERMUDAGRASS SPRING TRANSITION. K. Umeda*; University of Arizona, Phoenix, AZ (173)

ABSTRACT

Highly managed turfgrass is commonly overseeded with cool-season grasses on golf courses, sports turf fields, and even in residential and commercial landscapes. Spring transition is the process of removing the overseeded cool-season grass and re-establishing warm-season turf. Bermudagrass (Cynodon spp.), the warm-season turf, emerges from winter dormancy in the spring.  The overseeded cool-season grass that is most commonly used is perennial ryegrass (Lolium perenne). Perennial ryegrass is typically replaced by the emerging bermudagrass as summer temperatures intensify. Bermudagrass transition may be hastened through cultural practices such as, lowering the mowing height of cut, properly managing irrigation and fertility, and cultivation by vertical mowing or aerifying.  However, breeding has created perennial ryegrass cultivars that tolerate the heat and sometimes survive through the summer.  The surviving ryegrass competes against the bermudagrass, depriving it from reproducing and firmly establishing a foundation turfgrass. Elimination of the perennial ryegrass can be enhanced by the use of herbicides as transition aids.  The sulfonylurea (SU) herbicides have proven to be safe and effective in removing ryegrass.  The SU herbicides marketed for such use include chlorsulfuron, flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron. The SU herbicides as transition aids are used at low doses that range from 5 to 105 gm a.i./ha.  The SU herbicides provide professional turf managers options to eliminate the cool-season grass at a desired pace, either through product selection or rate adjustments.  Furthermore, turf managers have the option to consider the desired percentage of total removal, and the safety of the emerging bermudagrass. The SU herbicides have demonstrated variable degrees of their ability to completely remove the cool-season grasses, and the speed at which the overseeded turf is removed, depending on weather conditions and the health and vigor of the overseeded winter grass. Moreover, the rate at which the underlying bermudagrass matures to a dense turf stand largely depends on weather conditions during transition and the cultural practices employed throughout the summer growing season.  It is not uncommon for bermudagrass to struggle in tree-shaded areas or in golf course roughs that have a higher height of cut.  Furthermore, scheduling activities (golf tournaments or sports events) on the overseeded turf commonly takes precedence over agronomic practices and as such, the SU chemicals offer turf managers an alternative to schedule the cool-season grass removal around planned events.  The use of SU herbicides as transition aids enables turf managers to manipulate and optimize operations to maintain year around aesthetic and functional turfgrass surfaces.




SULFONYLUREA HERBICIDES FOR SEDGE & KYLLINGA CONTROL. F. H. Yelverton*1, P. C. Bhowmik2, T. W. Gannon1; 1North Carolina State University, Raleigh, NC, 2University of Massachusetts, Amherst, MA (174)

ABSTRACT

Purple nutsedge (Cyperus rotundus L.) and false-green kyllinga (Kyllinga gracillima Miq.) are common, rapidly spreading perennial weed species in turfgrass environments that prefer above normal soil moisture. Sedge incidence has increased in recent years in turfgrass systems, likely due in part to changes in herbicide programs. Although purple nutsedge is not as widely distributed as other Cyperus species, it has been described as the world’s worst weed because it is a serious competitor with more crops that any other weed in the world. False-green kyllinga is a rhizomatous perennial which is similar to green kyllinga (Kyllinga brevifolia Rottb.) and may be differentiated by seed morphology or flower timing. Sulfosulfuron is a sulfonylurea herbicide developed for postemergent weed control in wheat and select cool- and warm-season turfgrasses. Trifloxysulfuron is another sulfonylurea herbicide currently registered for postemergent weed control in cotton (Gossypium hirsutum L.), sugarcane (Saccharum spp.) and select warm-season turfgrasses. Field trials were conducted to evaluate sulfosulfuron and trifloxysulfuron for postemergent false-green kyllinga and purple nutsedge control. All treatments included NIS (0.25 % v/v) and were applied with a CO2-propelled backpack sprayer.  Sulfosulfuron (66 fb 66 g ai ha-1) and trifloxysulfuron (28 fb 28 g ai ha-1) provided acceptable (> 80%) false-green kyllinga and purple nutsedge control. Application volume did not influence the efficacy of evaluated treatments. These data indicate sulfosulfuron and trifloxysulfuron may offer effective sedge control in turfgrass environments.




SUFONYLUREA RESISTANCE IN WEEDS OF TURF: POTENTIAL FOR PREVENTION. C. Mallory-Smith*, R. Golembiewski; Oregon State University, Corvallis, OR (175)

ABSTRACT

Sulfonylurea herbicides provide excellent control of many grass and broadleaf weed species.  Sulfonylureas and other acetolactate synthase (ALS) inhibitors are classified as Group 2 herbicides and are considered high risk for selecting herbicide resistant weeds. There are more than 100 weed species with resistance to ALS inhibitors which is the largest number of resistant species for any herbicide Group. Chlorsulfuron was the first sulfonylurea herbicide to be sold and resistance was identified in 1987 within four years of its introduction. Nevertheless, sulfonylureas and other Group 2 herbicides are still widely used on both agricultural and nonagricultural sites. In turfgrass, sulfonylureas provide control of some very difficult to manage weeds such as annual bluegrass, spurge, wild onion, and nutsedge. The continual mowing of turfgrass provides a secondary weed management tactic that has probably delayed resistance especially in annual species. However, if prostate weeds are missed during mowing, they may be at greater risk for the selection of resistance because of repeated exposure to sulfonylurea herbicides without a secondary management tactic. Perennial weeds are also at greater risk for resistance because they may still reproduce even with repeated mowing.  The best method to prevent herbicide resistance is to reduce the weed population selection pressure by choosing herbicides from a different chemical Group. A second application of the same herbicide greatly increases the selection pressure and should be avoided whenever possible. The issue is the limited number of herbicides with different sites of action that are effective on difficult to control weeds such as nutsedge. Resistance is likely to occur with Group 2 herbicides unless they are integrated into a complete weed management program.




BENCHMARK STUDY: ECONOMICS OF GLYPHOSATE-RESISTANT WEED MANAGEMENT. D. R. Shaw*1, M. D. Owen2, S. C. Weller3, B. G. Young4, R. G. Wilson5, D. L. Jordan6, J. Weirich7; 1Mississippi State University, Mississippi State, MS, 2Iowa State University, Ames, IA, 3Purdue University, West Lafayette, IN, 4Southern Illinois University, Carbondale, IL, 5University of Nebraska, Scottsbluff, NE, 6North Carolina State University, Raleigh, NC, 7University of Missouri, Portageville, MO (176)

ABSTRACT

Glyphosate-resistant (GR) crops have changed the way growers manage weeds and implement control strategies. Since the introduction of GR crops, growers in many instances have relied on glyphosate almost exclusively to control a broad spectrum of weeds. This over-reliance on glyphosate has resulted in the evolution of glyphosate resistance in some weed species. Growers and scientist are concerned about the sustainability of GR crops and glyphosate. When a grower is making decisions about weed control strategies, economic costs and benefits of the program are primary criteria for selection and implementation. Studies across six states were initiated in 2006 to compare the economics of using a weed resistance best management practice (BMP) system with a grower’s standard production system. Resistance BMP systems recommended by university scientists were more costly, but provided similar yields and economic returns. Rotation of GR crops resulted in a higher net return (corn and soybean) compared to continuous GR crop (cotton or soybean) or rotating a GR crop with a non-GR crop (corn). Growers can implement weed resistance BMP systems with the confidence that their net returns will be equivalent in the short run and, in the long term, resistance BMP systems will prevent or delay the evolution of GR weeds in their fields, resulting in substantial savings. Whether a grower is risk neutral or risk averse, the optimal decision would be to adopt a weed resistance BMP when the expected loss in revenue is greater than 30% and the probability of resistance evolution is 0.1 or greater. However, if the probability of developing resistance increases to 0.3, then the best decision would be to adopt a weed resistance BMP when the expected loss is 10% or greater. Given the scenarios analyzed, risk neutral or risk averse growers should implement a weed resistance BMP with confidence that they made the right decision economically, and avoided the risk of lost revenue from resistance. If the grower wants to continue to see the same level of return adoption of BMP’s is required.




BENCHMARK STUDY: EFFICACY AND ECONOMICS OF WEED MANAGEMENT TACTICS OF GROWERS VERSUS UNIVERSITY RECOMMENDATIONS. B. G. Young*1, J. M. Matthews1, D. L. Jordan2, P. M. Dixon3, R. G. Wilson4, S. C. Weller5, M. D. Owen3, D. R. Shaw6; 1Southern Illinois University, Carbondale, IL, 2North Carolina State University, Raleigh, NC, 3Iowa State University, Ames, IA, 4University of Nebraska, Scottsbluff, NE, 5Purdue University, West Lafayette, IN, 6Mississippi State University, Mississippi State, MS (177)

ABSTRACT

From 2006 to 2009 a total of 155 commercial fields in Illinois, Indiana, Iowa, Nebraska, North Carolina, and Mississippi were established as research sites to compare the weed management tactics used in grower practices versus academic recommendations for use in glyphosate-resistant corn, cotton, and soybean production systems.  The academic recommendations were targeted at deterring detrimental shifts in weed populations and the selection of glyphosate-resistant weed species.  Each field was divided into two sections with half managed with grower practices and the other half using the academic recommendations.  Fields were categorized into three cropping systems:  1) a single continuous glyphosate-resistant (GR) crop, 2) a rotation of two GR crops, and 3) a GR crop rotated with a non-GR crop. 

Over the course of the study the academic recommendations rarely eliminated a glyphosate application compared to grower practices regardless of the cropping system.  Instead, academic recommendations gradually increased the use of other herbicides used in the form of residual herbicides or tank mixtures with glyphosate.  The frequency of residual herbicide use by growers in GR soybean (35%) is well below cotton and corn in which adoption is greater than 60%.  Residual herbicides and tank mixtures with glyphosate were similar in frequency for GR cotton whereas the use of residual herbicides was favored in both GR soybean and corn.  Academic recommendations for resistance management typically integrated PPO- and PSII-inhibiting herbicides when the target weeds included horseweed, waterhemp, Palmer amaranth, and giant ragweed.  The use of HPPD-, ALS-, and seedling shoot-inhibitor herbicides were also utilized depending on the specific target weed.  The management tactics employed by the academic recommendations typically resulted in lower weed population densities at both prior to and following a postemergence application containing glyphosate.  In broad terms, the diversification of herbicide tactics have resulted in improved weed management and similar economic returns for growers compared with their current practices.  However, grower adoption of integrated herbicide strategies continues to lag behind what would be deemed optimal to deter the evolution of glyphosate-resistant weeds, especially in certain cropping systems and geographies that have experienced less frequent problems with glyphosate efficacy to date.




MANAGING GLYPHOSATE-RESISTANT ITALIAN RYEGRASS IN THE MISSISSIPPI DELTA. J. A. Bond*, T. W. Eubank, R. C. Bond, V. K. Nandula; Mississippi State University, Stoneville, MS (178)

ABSTRACT

Italian ryegrass (Lolium perenne ssp. multiflorium) is an erect winter annual with a biennial-like growth habit.  It is often planted as a cover crop, as a temporary lawn grass, for roadside restoration, or for soil enrichment; however, it can escape cultivation and becomes established in fallow fields as a winter weed.  Glyphosate-resistant (GR) Italian ryegrass was first documented in the United States in Oregon in 2003.  Regionally, two populations of GR Italian ryegrass exhibiting a three-fold resistance were identified in field crops in Washington County, Mississippi, in 2005.  Surveys from 2009 indicate that GR Italian ryegrass is now present in 12 counties in the Mississippi Delta.  It has also become problematic in other southern states, including Arkansas, Louisiana, and North Carolina.  Glyphosate-resistant Italian ryegrass represents a serious threat to crop production systems in the midsouthern United States.  The presence of this weed also jeopardizes traditional glyphosate-based burndown programs.  Research to address management of GR Italian ryegrass was initiated at the Delta Research and Extension Center in Stoneville, Mississippi, in 2005.  The major conclusions of research from 2005 through 2008 were (1) postemergence options in the spring are extremely limited and require at least two herbicide applications to approach complete control and (2) residual herbicides applied in the fall offer the best opportunity for controlling GR Italian ryegrass.  Clomazone, metolachlor, pyroxasulfone, and trifluralin are residual herbicides that have provided the most consistent control of GR Italian ryegrass following applications in early November.  Clethodim and paraquat are the most effective postemergence herbicide options for GR Italian ryegrass.  However, depending on the timing of application, postemergence treatments often do not provide complete control.  Herbicide options are limited and Italian ryegrass has a history of rapidly developing resistance to multiple herbicide chemistries.  Therefore, the research emphases have transitioned to focus on programs for managing GR Italian ryegrass.  These include integration of postemergence and residual herbicides, tillage, and sanitation.  jbond@drec.msstate.edu




POTENTIAL TANK-MIX COMBINATIONS TO CONTROL GLYPHOSATE-RESISTANT GIANT RAGWEED IN COTTON. K. A. Barnett*, L. E. Steckel; University of Tennessee, Jackson, TN (179)

ABSTRACT

Glyphosate-resistant (GR) weeds are a major issue for Tennessee cotton growers. These GR weeds can be problematic to control when relying only on timely rains to activate pre applied herbicides.  GR horseweed, GR Palmer amaranth, and GR giant ragweed are the three GR weeds that can currently be found in Tennessee.  While GR giant ragweed has not spread as quickly as other GR species, it is a troublesome weed for growers to content with.  Therefore a study was constructed to examine herbicide treatments that effectively control GR giant ragweed in WideStrike cotton.  Treatments at the 1-leaf stage consisted of the following: glufosinate at 0.59 kg ai/ha, glyphosate at 0.84 kg ae/ha, glufosinate at 0.59 kg ai/ha plus glyphosate at 0.84 kg ae/ha, pyrithiobac sodium at .106 kg ai/ha plus non-ionic surfactant (NIS) at 0.25% v/v, glyphosate at 0.84 kg ae/ha plus pyrithiobac sodium at .106 kg ai/ha, glyphosate at 0.84 kg ae/ha plus glufosinate at 0.59 kg ai/ha plus pyrithiobac sodium at .106 kg ai/ha, and glufosinate at 0.59 kg ai/ha plus fluometuron at 0.56 kg ai/ha.  Treatments at the 5-leaf stage consisted of the following:  glyphosate at 0.84 kg ae/ha plus trifloxysulfuron at .008 kg ai/ha plus NIS at 0.25% v/v, glufosinate at 0.59 kg ai/ha plus pyrithiobac sodium at .106 kg ai/ha, glufosinate at 0.59 kg ai/ha plus fluometuron at 0.56 kg ai/ha, and glufosinate at 0.59 kg ai/ha plus fluometuron at 1.12 kg ai/ha.  One treatment was glufosinate applied at 0.59 kg ai/ha at the 1-leaf stage and followed by (fb) glufosinate at 0.56 kg ae/ha at the 5-leaf stage.  The objective of this study was to determine crop response to herbicide treatments, control of GR giant ragweed, and the effect of these treatments on yield.  The experiment was a randomized complete block design with three replications.  An analysis of variance was performed to separate differences between treatments at p<.05.  Crop injury, GR giant ragweed control, and yield were significant at p<.05.  Injury 3 wks after the 5-leaf application ranged from 11 to 60 % on a scale of 0 % (no injury) to 100 % (crop dead).  Treatments with glufosinate plus fluometuron (all rates and application timings), glufosinate plus pyrithiobac sodium, and glyphosate plus trifloxysulfuron resulted in the highest amount of injury.  Seven days after the 5-leaf application, GR giant ragweed control ranged from15 to 96%.  Glufosinate plus fluometuron (1.12 kg ae/ha), glufosinate plus fluometuron (0.56 kg ae/ha), glufosinate fb glufosinate, and glufosinate plus pyrithiobac sodium resulted in greater than 90 % GR giant ragweed control.  Herbicide treatments also impacted yield.  Glufosinate plus glyphosate resulted in the highest yield (926 kg/ha) followed by glufosinate alone (854 kg/ha), glyphosate plus glufosinate plus pyrithiobac sodium (781 kg/ha), glyphosate plus pyrithiobac sodium (765 kg/ha), glufosinate fb glufosinate (755 kg/ha), and glyphosate alone (725 kg/ha).  All other herbicide treatments resulted in a yield of less than 700 kg/ha and significantly reduced yield when compared with the highest yielding treatment.  With the exception of glufosinate fb glufosinate, all other treatments that resulted in greater than 90 % control of giant ragweed also had the highest crop injury which resulted in decreased yield.  Results indicate that applying glufosinate fb glufosinate is the best option to achieve greater than 90% control of GR giant ragweed without decreasing crop yield. 




MANAGMENT OF GLYPHOSATE-RESISTANT PALMER AMARANTH IN ROUNDUP READY SOYBEANS. L. E. Steckel*, K. A. Barnett; University of Tennessee, Jackson, TN (180)

ABSTRACT

MANAGMENT OF GLYPHOSATE-RESISTANT PALMER AMARNANTH IN ROUNDUP READY SOYBEANS. Lawrence E Steckel* and Kelly A Barnett; University of Tennessee, Jackson, TN (180)
Glyphosate-resistant (GR) weeds are a major issue for Tennessee soybean growers. GR horseweed, GR giant ragweed, and GR Palmer amaranth are the three GR weeds that can currently be found in Tennessee. Of these three weeds GR Palmer is the most problematic as it causes the most yield loss and is the hardest to control with post emergence applications.  Currently growers are managing GR weeds with pre- emergence (PRE) applied herbicides often followed by an early post emergence application that contains a residual for GR weeds.  Growers often ask which herbicides provide the most residual for Palmer amaranth and which PRE followed by a POST application is the best system.   

 

Two studies were conducted that evaluated the length of residual activity of different PRE applied herbicides and which of these PREs followed by a POST was the best system.  The studies were conducted near Millington, TN on a field that had a natural, heavy infestation of GR Palmer amaranth.  Study 1 examined the length of residual activity of herbicides applied at soybean planting. The herbicides examined were metribuzin + S-metalochlor, flumioxazin + chlorimuron, flumioxazin, fomesafen + S-metalochlor, pendimethalin and pyroxisulfone + flumioxazin.

 

Study 1 showed that fomesafen + S-metalochlor and pyroxasulfone + flumioxazin provided the longest residual control of 30 days.  Flumioxazin and metribuzin + S-metalochlor provided 21 days of control. Flumioxazin + chlorimuron provided 14 days of control and pendimethalin 5 days.   This study demonstrated that fomesafen + S-metalochlor and pyroxasulfone + flumioxazin provided the longest residual for Palmer amaranth

 

Study 2 evaluated different systems where a PRE was followed by an early POST (Palmer amaranth 10 cm tall) emergence application. The systems examined in this study were metribuzin + S-metalochlor followed by fomesafen, or cyanazine or lactofen.

This study demonstrated that a PRE that provides good residual control of Palmer amaranth followed by a timely POST application can provide consistent control of GR Palmer. 

 

 




CONTROL OF HPPD-RESISTANT WATERHEMP IN CORN AND SOYBEANS. G. D. Vail*1, C. L. Foresman1, N. D. Polge2, V. K. Shivrain1, D. A. Thomas3; 1Syngenta, Greensboro, NC, 2Syngenta, Vero Beach, FL, 3Syngenta, Monticello, IL (181)

ABSTRACT




COMPETITION OF TRANSGENIC VOLUNTEER CORN WITH SOYBEAN AND IMPLICATIONS FOR WEED AND INSECT RESISTANCE MANAGEMENT. P. T. Marquardt*, C. H. Krupke, W. G. Johnson; Purdue University, West Lafayette, IN (182)

ABSTRACT

Glyphosate-resistant volunteer corn is a problematic weed in corn/soybean rotational systems.  This issue is partially due to the increasing prevalence of stacking both glyphosate and insect-resistant (mainly Bt) traits into the same genetically-modified plant.  Volunteer corn (Zea mays) expressing Bt traits, which target the western corn rootworm (Diabrotica virgifera virgifera) (WCR), may potentially increase the Bt selection pressure on WCR populations.  Volunteer corn can also compete with soybean, lowering yields.  The objectives of this study were to determine how WCR emergence is affected by different densities of volunteer corn and to quantify the impact of volunteer corn on soybean growth and yield.  Volunteer corn seed was hand-planted at densities ranging from 0.5 to 16 plants/m2 within soybean plots.  Densities were established at soybean planting and two weeks after planting to account for early and late emerging corn.  WCR emergence was assessed using field emergence traps placed over individual corn plants in the 0.5 and 16 plants/m2 plots.  Data collected included the adult emergence of WCR, corn leaf area, dry weight (corn and soybean), and soybean yield.  Twice as many adult WCR emerged from a single volunteer corn plant in 16 plants/m2 plots compared to 0.5 plants/m2 plots. Soybean yield reductions were 1516 kg/ha in the early planted 16 plants/m2 plots.  Yield reductions in 2008 and 2009 occurred when 2 and 4 plants/m2, respectively, emerged at the same time as soybean.  No soybean yield loss occurred when volunteer corn emerged after soybean.  Our results show that controlling volunteer corn will not only prevent soybean yield loss, but it may decrease Bt selection pressure on WCR populations.




GROWER ATTITUDES REGARDING GLYPHOSATE RESISTANCE: A FIVE YEAR FOLLOW-UP TO THE BENCHMARK STUDY. J. M. Prince*1, D. R. Shaw1, W. A. Givens1, S. C. Weller2, B. G. Young3, R. G. Wilson4, M. D. Owen5, D. L. Jordan6; 1Mississippi State University, Mississippi State, MS, 2Purdue University, West Lafayette, IN, 3Southern Illinois University, Carbondale, IL, 4University of Nebraska, Scottsbluff, NE, 5Iowa State University, Ames, IA, 6North Carolina State University, Raleigh, NC (183)

ABSTRACT

Nearly 1,300 growers participated in a 2010 survey to determine their attitudes and awareness regarding glyphosate-resistant (GR) weeds and the way in which these weeds had affected their weed management practices.  An additional 350 growers were included in the survey, representing a subset of a 2005 Benchmark Survey.  Their answers were compared across time so that cross-sectional and longitudinal comparisons could be made.  Most growers surveyed in the 2010 survey were aware of the potential for weeds to evolve resistance to glyphosate but were not aware of glyphosate resistance in specific weeds in their county or state.  The South region was different however, and growers were significantly more aware of local cases of GR weeds.  For grower participated in both 2005 and 2010 surveys, awareness of GR weeds did not increase appreciably.  What did change, however, was their perception of the severity of the problems incurred with GR weeds.  Occurrence of GR weeds on-farm in 2010 was up considerably from 2005.  Growers in the South were more likely to report instances of on-farm GR weeds.  Growers in the South were also more likely to consider glyphosate resistance a serious problem.  Across both 2005 and 2010 surveys, 30% of growers did not consider GR weeds to be a problem. 



BENCHMARK STUDY: FOUR YEARS LATER - TRENDS IN WEED SPECTRUM AND POPULATION DENSITY. M. D. Owen1, S. C. Weller*2, D. R. Shaw3, B. G. Young4, D. L. Jordan5, R. G. Wilson6, P. M. Dixon1; 1Iowa State University, Ames, IA, 2Purdue University, West Lafayette, IN, 3Mississippi State University, Mississippi State, MS, 4Southern Illinois University, Carbondale, IL, 5North Carolina State University, Raleigh, NC, 6University of Nebraska, Scottsbluff, NE (184)

ABSTRACT

The Benchmark Study was initiated in 2006 and represents the largest and longest term field-scale study established to assess the impact of production practices on weed management with a focus on the sustainability of the glyphosate-based crop production systems.  The Benchmark Study was conducted on 156 fields in Illinois, Indiana, Iowa, Mississippi, Nebraska and North Carolina and over the five years that the study has been maintained an excess of  170,000 observations and samples have been collected.  These samples included soil samples from which seed banks were enumerated and four weed density assessments by species; before or at planting; before the first postemergence herbicide application; two weeks after the last postemergence herbicide treatment;  and before harvest.  Treatments represented prevalent grower practices which focused exclusively on glyphosate for weed control and best management practice recommendations.  Crop production systems included continuous glyphosate-resistant corn, soybean and cotton, glyphosate-resistant corn rotated with glyphosate-resistant soybean and glyphosate-resistant soybean rotated with conventional corn.   One side of each field had weed management as determined by the grower and the other side was managed using academic recommendations.  Generally, the weed population densities were less on the portion of the field managed using academic recommendations compared to the grower side.  Weed population densities were higher in continuous crops when compared to crop rotations.  Continuous cotton had generally greater weed population densities and differences between treatments when compared with continuous corn and soybean and continuous corn had the lowest weed population densities.  Where glyphosate-resistant corn and soybean rotation was compared with glyphosate-resistant soybean and conventional corn rotation, weed population densities were similar.  Weed population densities generally declined with the later in-season observations; however seedbanks did not consistently decline during the time period that the Benchmark Study was conducted.  Species richness did not change regardless of the crop rotation and remained similar during the course of the study.  Continuous corn production systems had the lowest species richness while continuous cotton and soybean had similar richness values.  Crop rotation, geography, and diversification of herbicide use can all influence weed populations and should be considered at a local level in efforts that would contribute towards greater sustainability of modern crop production systems in the USA.




POSTEMERGENCE WEED CONTROL IN SORGHUM CONTAINING THE DUPONT™ INZEN™ AII AND INZEN™ Z HERBICIDE TOLERANCE TRAITS. R. N. Rupp*1, E. Castner2, R. Edmund2, M. Edwards2, J. Harbour2, C. Medlin2, D. W. Saunders3; 1DuPont Crop Protection, Edmond, OK, 2DuPont Crop Protection, Wilmington, DE, 3DuPont Crop Protection, Johnston, IA (185)

ABSTRACT

Postemergence control of grasses in sorghum has been identified as a highly prioritized research need by sorghum producers. To meet this need, two new herbicide tolerance traits are under development by DuPont that will enable postemergence control of grass weeds in sorghum. The two separate traits were first identified by researchers at Kansas State University and confer tolerance to quizalofop and sulfonylurea herbicides. In 2010, DuPont and University researchers evaluated one-pass postemergence and two-pass preemergence followed by postemergence herbicide programs for grass control in grain sorghum. Data will be presented supporting the use of quizalofop and sulfonylurea herbicides in grain sorghum containing the tolerance traits as new tools for postemergence grass control across the United States. Data will also be presented showing that SU tolerant sorghum has tolerance to residues of ALS herbicides in the soil which may allow for shortened rotational crop intervals following applications of herbicides such as chlorsulfuron and pyrithiobac sodium. Seed products with the tolerance traits will be available for sale pending development by seed companies.  DuPont Crop Protection herbicides for use on the tolerant sorghum are being evaluated and will be available for sale pending EPA registration.




STEWARDSHIP OF DUPONT™ INZEN™ AII AND INZEN™ Z HERBICIDE TOLERANT TRAITS IN SORGHUM. D. R. Forney*1, D. W. Saunders2, C. B. Hazel3, R. N. Rupp4; 1DuPont Crop Protection, Newark, DE, 2DuPont Crop Protection, Johnston, IA, 3DuPont Crop Protection, Wilmington, DE, 4DuPont Crop Protection, Edmond, OK (186)

ABSTRACT

Stewardship of DuPont™ Inzen™ AII and Inzen™ Z Herbicide Tolerance Traits in Sorghum.

 

D. R. Forney*, David W. Saunders,Christine B. Hazel, and Robert N. Rupp, DuPont Crop Protection, Wilmington, DE

 

Raymond.forney@usa.dupont.com

Sorghum growers consistently highly rank the need for postemergence grass control technology.  Scientists at Kansas State University developed sulfonylurea- and quizalofop-tolerant sorghum breeding lines by integrating native traits.  Each trait provides differential tolerance within the herbicide modes of action. The quizalofop tolerance trait does not provide tolerance to the cyclohexanedione herbicides. DuPont is commercializing the technologies. Anticipated benefits include that sorghum producers will have greater opportunity for a better crop, yield and profit, with proven herbicide active ingredients that are new for sorghum. Growers will have more options to clean up grasses that come up in the crop. Stewardship has been recognized since project inception as a critical success factor.  Staggered launch will establish a foundation for stewardship best management practices. Sustainably achieving the technology benefits requires substantial collaboration among numerous stakeholders. Several factors are considered “in scope” for stewardship effort, including: 1) trait expression (consistent, reliable, dependable performance of traited seed); 2) absence of  unacceptable metabolites or unintended constituents; 3) accurate prediction of weed shifts; 4) potential evolution of resistant weed biotypes based on gene flow in Sorghum spp.; 5) potential evolution of R biotypes based on herbicide selection pressures in Sorghum spp.: 6) practical, effective weed management strategies and recommendations;  7) marketing/promotion consistent with data; and 8) technical and public acceptance/support of stakeholders. The risk of pollen-mediated trait transfer among Sorghum spp. is among the most significant of these, especially considering the prior presence of glyphosate-resistant johnsongrass in some sorghum growing states. Among many tactics that are important for weed resistance management, three are considered by DuPont Crop Protection to be fundamental on any given field: 1) use of an effective alternate mode-of-action herbicide (MOA) to control known herbicide-resistant weeds; 2) including an effective alternate MOA at least every-other year for “at-risk” weeds; and 3) scouting fields to monitor effectiveness of the herbicide program.  Stewardship best management practices are expected to include:  1) planting traited seed only in fields where crop rotation allows for use of an effective alternate mode-of-action herbicide within a warm season between successive sorghum crops; 2) planting traited seed only where glyphosate-, quizalofop-, or ALS-resistant johnsongrass is not already present; 3) preventing Sorghum spp. weeds from flowering within a certain distance during the pollination window of the sorghum crop; 4) scouting and rapid response to identify and prevent reproduction of potentially resistant escapes and volunteers; and 5) ongoing research to understand and refine the stewardship best practices that can ensure sustainability for the technology.




ANNUAL STRAWBERRY TOLERANCE TO HERBICIDES APPLIED UNDER POLYETHYLENE MULCH. A. W. MacRae*, R. Kelly; University of Florida/IFAS, Wimauma, FL (187)

ABSTRACT




WEED MANAGEMENT IN GREEN ONIONS WITH OXYFLUORFEN. D. Doohan*, T. Koch; The Ohio State University, Wooster, OH (188)

ABSTRACT

Labor for weed control in green onions can cost more than $500/ acre. Approximately 400 acres are produced in Ohio annually mostly on muck soils, and about 5% of the annual acreage is never harvested because of weeds. Dimethenamid can be applied PRE but control does not last through harvest of this 60 day crop. Thus there is a great need to identify and seek registration of herbicides that can be used to control late emerging weeds postemergence. Experiments were conducted at the Ohio Agricultural Research and Development Center Muck Crops Research Station in 2006 through 2009 to quantify the tolerance of green onions to the Goaltender formulation of oxyfluorfen. A randomized complete block design with four replications was used. Plots were maintained weed free until oxyfluorfen application at the 2-leaf growth stage. Ishikura green onions were used each year; except 2007 when White Spear was also grown. Oxyfluorfen was applied at 35, 70, 105 and 209 g/ha in 234 L/ha water. The 209 g/ha treatment was included as a 2X rate. Plots were visually rated for weed control and crop injury at 1, 3 and 6 WAT. Yield was recorded. Data were analyzed by SAS and orthogonal contrasts used to detect treatment differences. Injury was difficult to detect even at 209 g/ha; however, occasionally the 2X rate caused stunting that was statistically significant. Even with this worst-case scenario yield was unaffected because of the weed control provided. Weed control, mainly prostrate pigweed and purslane was optimized with 70 and 105 g/ha.  





PREEMERGENCE AND POSTEMERGENCE HERBICIDES FOR MAXIMUM WEED CONTROL IN DRY BULB ONION. B. H. Zandstra*, C. M. Herrmann, R. V. Tocco Jr.; Michigan State University, East Lansing, MI (189)

ABSTRACT

Field experiments were conducted on direct-seeded onions grown on muck soils in 2008, 2009, and 2010 to evaluate several PRE and POST herbicides. PRE herbicides were applied at seeding, at the 2 leaf stage (LS), and again at the 4-5 LS. In 2009 and 2010, PRE application of pendimethalin ACS at 4.4 kg/ha provided better control of ladysthumb (Polygonum persicaria) and redroot pigweed (Amaranthus retroflexus) than the labeled rate of pendimethalin ACS (2.2 kg/ha).  The 2X rate of pendimethalin ACS did not cause onion injury or stand thinning in any year, and in 2010 onion yield at the 4.4 kg/ha rate was significantly higher than the 2.2 kg/ha rate, probably due to reduced weed competition at the higher rate. S-metolachlor at 1.46 kg/ha, dimethenamid-p at 1.10 kg/ha, acetochlor at 1.12 kg/ha, or propachlor at 4.5 kg/ha reduced yellow nutsedge (Cyperus esculentus) stand in 2008 and 2009. Propachlor did not cause onion injury in any year and gave moderate to good control of many common grass and broadleaf weeds. PRE application of s-metolachlor, dimethenamid-p, or acetochlor resulted in significant onion stunting in all years. PRE application followed by 2 POST applications of s-metolachlor resulted in yield reduction in 2008. Sequential application of acetochlor caused yield reduction in 2008 and 2010. Preemergence application of flumioxazin at 0.036 kg/ha caused slight stunting in 2010 but did not result in yield reduction in any year. Flumioxazin provided good control of common lambsquarters (Chenopodium album), redroot pigweed, common purslane (Portulaca oleracea), and marsh yellowcress (Rorippa islandica). Ethofumesate applied at 1.12 kg/ha provided burndown activity on common lambsquarters, common purslane, and spotted spurge (Euphorbia maculata) but did not provide preemergence control on muck soil.

Flumioxazin applied POST at 0.036 or 0.072 kg/ha to onions at the 2 and 4 LS provided excellent burndown control of small common lambsquarters, redroot pigweed, and common purslane. At both rates and timings, onion injury was minimal and no yield reduction was observed in any year. In another trial, early-season weed control with oxyfluorfen SC applied at rates of 0.04, 0.07, 0.13 or 0.21 kg/ha was compared to oxyfluorfen EC applied at equivalent rates. In 2008 and 2009, control of ladysthumb was slightly better with oxyfluorfen EC than with similar rates of oxyfluorfen SC applied at the 1 LS.  Delaying oxyfluorfen SC application until the 2 LS dramatically reduced weed control efficacy, as the larger weeds were more difficult to control. Oxyfluorfen EC applied at the 2 LS provided better control of all weeds present when compared to equivalent rates of oxyfluorfen SC. Fluroxypyr applied at 0.14 or 0.28 kg/ha provided moderate to good control of ladystumb, common purslane, and spotted spurge but resulted in serious onion injury in all years and yield reduction in 2008 and 2010. Bromoxynil provided excellent control of ladysthumb but was weak on common purslane in all years. 



EVALUATION OF PRE APPLICATION OF S-METOLACHLOR AND DIMETHENAMID-P ON DIRECT SEEDED ONIONS USING ACTIVATED CARBON. J. Felix*, K. Osborne, J. Ishida; Oregon State University, Ontario, OR (190)

ABSTRACT

A field study was conducted in 2010 at Oregon State University, Malheur Experiment station, Ontario, OR to evaluate the potential use of activated charcoal to detoxify s-metolachlor and dimethenamid-p applied pre-emergence (PRE) to direct seeded onion. The study was a split-split plot design with irrigation (with and without) forming the main blocks to which activated carbon (with and without) and herbicide treatments were superimposed. The study had four replications and the plot size was 2.24 m wide (4 rows) by 6.6 m length. A precision onion planter was modified to simultaneously apply 2.54 cm activated charcoal slurry directly over the row in a single pass. Activated charcoal was applied at 28 kg/ha in 33 L/ha of water. Herbicides were applied immediately after planting using a backpack CO2 sprayer fitted with 8002 nozzles. Pre-emergence s-metolachlor was applied at 1.07 or 1.42 kg ai/ha, while dimethenamid-p was applied sequentially at 0.55 kg ai/ha PRE and POST or 1.1 kg ai/ha PRE. The study included a grower standard treatment, which was comprised of pendimethalin at 1.07 kg ai/ha PRE followed by s-metolachlor at 1.42 kg ai/ha when onions were at 2-leaf stage. An untreated control was also included. Onion plant stand was reduced when irrigation was applied subsequent to s-metolachlor and dimethenamid-p PRE without activated charcoal regardless of the herbicide rate. Analysis of variance indicated an activated charcoal-by-irrigation interaction for onion plant stand. Onion stand at 34 days after planting averaged 163,970 plants/ha when herbicides were applied without activated charcoal and followed by irrigation compared to 205,207 plants/ha with activated charcoal and irrigation. Plant stand was also affected by the presence of onion maggot (Delia antiqua) in the study area. There also was a herbicide-by-irrigation interaction for onion plant stand. Overall, the plant stand was reduced when s-metolachlor and dimethenamid-p treatments were followed by irrigation. Marketable onion yield for plots not treated with activated charcoal was reduced 11% relative to charcoal treated plots (43 T/ha). There also was a herbicide-by-irrigation interaction for marketable onion yield. The irrigated plots had relatively low yield compared to non-irrigated plots treated with different rates of s-metolachlor and dimethenamid-p. Marketable onion yield was similar for plots treated with activated charcoal with and without irrigation, which was 40 and 46 T/ha, respectively. The results indicate that the use of activated charcoal may be a viable option for pre-emergence application of s-metolachlor and dimethenamid-p to directed seeded onion. However, more studies are needed to confirm these results.




POSTEMERGENCE WEED CONTROL IN SNAP BEAN, CARROT, AND LETTUCE USING A PRECISION-GUIDED FLAME WEEDER. C. M. Herrmann*, R. V. Tocco Jr., B. H. Zandstra; Michigan State University, East Lansing, MI (191)

ABSTRACT

Experiments were conducted in 2008, 2009, and 2010 to evaluate postemergence weed control with a shielded propane flame weeder. Propane was applied at 0.07, 0.14, and 0.28 mPa at ground speeds of 1.6, 3.2, or 6.4 km/h. Under these parameters, propane fuel consumption ranged from 16.5 to 190.1 kg/ha. Experiments were conducted in snap bean, carrot, and lettuce. Each crop was planted with three rows per bed with row spacing of 41 cm. An Eco-Dan camera and computer guidance system was installed to detect the crop row pattern and allow for precise orientation of the flame weeder in relation to the crop rows. Approximately 90% of the total plot area was flamed, with a 5 cm wide band centered on each crop row which remained unflamed. 

Treatments were applied when snap beans had one expanded trifoliate leaf and weeds had 4-6 true leaves. Treatments were applied to carrots when plants had at least one full fern leaf and weeds had 4-8 leaves. Lettuce was treated approximately one month after seeding. Beans treated at 1.6 km/h were injured, and injury increased from 23 to 59% with increasing propane pressure. Treatments with ground speeds greater than 1.6 km/h did not result in serious snap bean injury in any year.  The highest dosage (190.1 kg/ha) resulted in bean yield reduction in both 2009 and 2010. Carrots were more susceptible to thermal injury than snap beans, and selectivity was difficult to achieve in carrot under the parameters tested. Carrot ferns often regrew after flaming, and there was no detectable difference in carrot yield among treatments. Lettuce cultivars varied in their susceptibility to heat injury, and leaf lettuce was the most sensitive variety. Propane doses over 100 kg/ha caused yield reduction in leaf lettuce and head lettuce in 2010, but no yield reduction was detected at any dosage for Romaine lettuce.

Visual ratings, weed counts, and weed biomass were assessed for several weeds, including redroot pigweed (Amaranthus retroflexus), common lambsquarters (Chenopodium album), common purslane (Portulaca oleracea), and large crabgrass (Digitaria sanguinalis). Propane pressures of 0.14 and 0.28 mPa with ground speeds of 1.6 or 3.2 km/h controlled 64-94% of redroot pigweed and common lambsquarters. Common purslane and large crabgrass were more difficult to control and often regrew, but 80% control of common purslane and 89% control of large crabgrass was achieved when treated at 190.1 kg/ha. The precision-guided flame weeder may provide a useful tool for vegetable growers seeking an effective method of non-chemical weed control, but consideration must be given to crop choice, application timing, and the weed species present.



EVALUATION OF AN IN-ROW ROTATING CULTIVATOR IN VEGETABLE CROPS. S. A. Fennimore*1, R. F. Smith2, J. Rachuy2; 1University of California, Davis, Salinas, CA, 2University of California, Salinas, CA (192)

ABSTRACT

The objective of this project was to test a robotic intra-row cultivator in California vegetable production systems and to determine if it can be used to thin lettuce as well as remove in-row weeds from within lettuce and tomato seed lines. The overall project goal is to reduce hand weeding costs in vegetable crops.  Currently the only way to remove weeds from within the crop row is by hand weeding and selective herbicides.  The Tillett and Hague rotating cultivator (a robotic cultivator), sold commercially in the United Kingdom, is capable of removing weeds from within the crop row.  Direct-seeded crops are generally planted at high stands and then thinned by hand to desired stands at costs of $200 to $370 ha-1.  An intra-row cultivator could reduce production costs for direct-seeded crops like lettuce, if hand weeding can be reduced or eliminated.  Field studies were conducted on direct-seeded lettuce and transplanted lettuce and tomatoes during 2009 and 2010 at the USDA-ARS research farm near Salinas, CA to evaluate an intra-row cultivator.  The Tillett and Hague cultivator uses machine vision to recognize the patterns of the crop row. A rotating cultivator shoe rotates within the crop row, with a cutaway wedge that is automatically aligned with the desired crop plant and removes weeds within the row between the desired crop plants. The Tillett and Hague rotating cultivator was compared to a standard cultivator equipped with cultivator knives to remove inter-row weeds.  The trials were arranged in a split-plot design with cultivator as the main plot and herbicide as the split plot. Treatments were replicated four times. Pronamide was applied preemergence in seeded lettuce and pre-transplant in transplanted lettuce at 1.35 kg ai ha-1. In tomato rimsulfuron was applied pre-transplant at 35 g ha-1 followed by trifluralin at layby at 0.84 kg ha-1.  Weed density, hand thinning/weeding time, crop stand, crop injury and crop yield evaluations were measured. Analysis of variance (ANOVA) and mean separation by either LSD (P= 0.05) or Duncan’s (P=0.05) was performed on all data.

 

In June 2009 a commercial direct-seeded lettuce planting near Gonzales, CA was thinned and weeded with the rotating cultivator. After machine thinning with the rotating cultivator and inter-row cultivation with the standard cultivator, the trial was hand thinned. The standard cultivator required 28.6 hr ha-1 to thin, while plots thinned with the rotating cultivator required 10.3 hr ha-1 to hand thin a 64% reduction in labor input. The trial was repeated in June 2010 and a 51% reduction in thinning labor was realized in the rotating vs. standard cultivator, respectively.

 

In May 2009 a direct-seeded lettuce trial at the USDA-ARS research farm near Salinas, CA was conducted similar to the Gonzales study. After machine thinning with the rotating cultivator and inter-row cultivation with the standard cultivator, the trial was hand thinned.  The total hand thinning and weeding in the rotating cultivator treatment was 53.4 hr ha-1 compared to 77 hr ha-1 in the standard cultivation plots, for a 31% reduction in hand weeding effort in the rotating cultivator vs. standard cultivator treatments.  The trial was repeated in June 2010 and a 32% reduction in thinning labor was realized in the rotating vs. standard cultivator, respectively.




USING LESS ATRAZINE IN SWEET CORN: CHALLENGES TO OVERCOME. M. M. Williams II*1, R. A. Boydston2, E. Peachey3, D. E. Robinson4; 1USDA-ARS, Urbana, IL, 2USDA-ARS, Prosser, WA, 3Oregon State University, Corvallis, OR, 4University of Guelph, Ridgetown, ON (193)

ABSTRACT

In the near future, growers may see further restrictions on their most widely used weed control tactic - atrazine.  Studies were conducted throughout the major processing sweet corn growing areas in North America to determine the impact of using less atrazine postemergence on sweet corn production.  In a total of eight environments, results showed atrazine's contribution to weed control and yield protection were greatest when other aspects of weed management resulted in poor (<50%) weed control.  Sweet corn production did not benefit from atrazine in every environment, but most.  Addition of atrazine postemergence with an HPPD-inhibiting herbicide not only improved mean control of individual weed species and species groups, but also reduced variation in weed control and crop yield responses.  Also, deleterious responses from reduced atrazine use were less severe in a vigorous growing hybrid, compared to a weakly growing hybrid.  Currently, most sweet corn fields suffer yield loss due to weed interference.  Atrazine is inexpensive, enhances performance of most other available herbicides, and is used widely.  Simple, economically viable alternatives to atrazine do not exist.  Further reductions in atrazine use, or a complete ban, are conceivable.  Our research shows further restriction of atrazine use likely will necessitate migration towards more complex weed management systems utilizing a variety of control tactics.



CAN LINURON REPLACE ATRAZINE IN SWEET CORN? J. B. Masiunas*, D. Anderson, L. Sun, X. Zhu; University of Illinois, Urbana, IL (194)

ABSTRACT

Atrazine is the standard broadleaf herbicide for sweet corn. The USEPA is reevaluating atrazine because of concerns about the environmental impact especially on water quality. Sweet corn in Illinois is often grown on sandy soils with shallow ground water tables. Alternatives are needed to reduce atrazine use in these environmentally-sensitive areas. Our objective was to determmine if linuron alone or combined with other broadleaf herbicides, including atrazine, could be used on swet corn. Linuron had excellent sweet corn safety when used alone or combined with atrazine, mesotrione, or nicosulfuron. Linuron also controlled (>95%) Amaranthus species, the dominate broadleaf weed species. Further evaluation is necessary to determine tolerance of sweet corn inbreds and hybrids to linuron.



INDAZIFLAM APPLIED ALONE AND IN TANKMIXTURE WITH OTHER HERBICIDES FOR WEED CONTROL IN PERENNIAL CROPS. D. Unland*1, H. Mager2, M. Edenfield3; 1Bayer CropScience, Research Triangle Park, NC, 2Bayer CropScience, Fountain Hills, AZ, 3Bayer CropScience, Lake Wales, FL (195)

ABSTRACT

Bayer CropScience anticipates registration of a new herbicide active ingredient, indaziflam, for use in perennial crops in 2011.  The brand name for this cellulose biosynthesis inhibiting (CBI) herbicide will be Alion.  Similar to other CBI herbicides it provides primarily preemergent control of weeds.  It is anticipated that most applications in perennial crops will be made with herbicides that offer postemergent control of existing weeds.  Various tankmix partners were evaluated in field trials for use when weeds have already emerged.  Additionally, combinations with other residual control herbicides were tested to determine if there would be any improvement in weed control.  When Alion was applied alone to existing weeds without other herbicides, weed control was not acceptable.  Control of existing weeds was achieved by adding glufosinate or glyphosate to Alion and was similar to the control provided by the postemergent herbicide applied alone.  Adding other residual herbicides improved control of certain weeds in some cases.




AN UPDATE ON THE PENDING NEW REGISTRATIONS OF FLAZASULFURON IN THE UNITED STATES. M. D. Grove*; ISK Biosciences, Spring, TX (196)

ABSTRACT

Flazasulfuron is registered under the trade name of Katana for use in warm season turf.  Further registrations are expected in the fall of 2011 for control of weeds on grape, citrus, sugarcane, Christmas trees and vegetation management.  Flazasulfuron has both pre-emergence and post emergence activity and provides control of a broad range of grasses, sedges and broadleaf weeds.  Flazasulfuron has been shown to be safe to the above listed crops when used according to label instructions.




THE IR-4 PROJECT: UPDATE ON WEED CONTROL PROJECTS. M. Arsenovic*1, D. L. Kunkel2, J. J. Baron2; 1IR-4 Project, Princeton, NJ, 2Rutgers University, Princeton, NJ (197)

ABSTRACT




ECOLOGY AND MANAGEMENT OF NATALGRASS (MELINIS REPENS) IN FLORIDA. C. Stokes1, G. MacDonald*1, K. Langeland1, C. Reinhardt-Adams1, D. Miller2; 1University of Florida, Gainesville, FL, 2University of Florida, Milton, FL (198)

ABSTRACT

Natalgrass (Melinis repens (Willd.) Zizka) is a species native to south central Africa.  Introduced to the U.S. in the 1800s, natalgrass was grown as a hay crop in central Florida in the early 1900s.  Although no longer cultivated, natalgrass is still common throughout much of the state.  As the restoration of native plant communities becomes increasingly important, land managers are struggling to control this species.  To develop an effective management plan, more information is needed about seed biology and ecology as well as the chemical management of natalgrass.

 

Natalgrass seeds were exposed to various light, temperature, pH and osmotic potential treatments to characterize seed germination conditions.  Natalgrass was shown not to require light for germination.  Maximum germination occurs between 20 and 35 C and at pH levels ranging from 6 to 8.  Germination did not occur at water potentials less than -0.2 MPa.  Natalgrass seeds were buried at different depths to determine maximum depth of emergence.  Natalgrass seeds emerged from a depth of 5 cm, the greatest depth tested in the study.  Preliminary tests also ip tndicate natalgrass requires an afterripening period after seed shed to reach maximum potential for germination.

 

Natalgrass seed longevity was studied under field conditions.  Under simulated burial conditions, seed showed an initial decline in germination after 3 months, with no further decline up to and including 15 months.  These results indicate the onset of dormancy in natalgrass seeds after burial.  This finding will be useful to land managers who plan to utilize tillage for natalgrass control, a practice that buries seeds.  Seed longevity was also studied on the ground surface, where dense layers of seeds form in infested areas.  Exclusion frames were placed over seed deposits to prevent further seed rain and germination under the frames was monitored for 12 months.  After 1 month, high levels of germination occurred, but levels declined to 0 seedlings/m2 within 2-3 months.  This finding indicates that surface seed deposits are quickly depleted if land managers can prevent further seed production. 

 

A number of herbicides were tested in the greenhouse and in the field to determine potential for natalgrass control pre- and postemergence.  Metsulfuron and fluazifop offered little or no control.  Glyphosate provided excellent control, but the lack of residual activity resulted in immediate reinfestation under field conditions.  Pendimethalin and metolachlor offered good control preemergence, but were detrimental to native species recrutiment.  Hexazinone and sulfometuron provided good control pre- and postemergence, but were also detrimental to native species.  Imazamox, imazapyr and imazapic offered less control but stunted growth and delayed flowering.  These herbicides were also less harmful to native species.  Of these compounds, imazapic provided the best combination of native plant tolerance and natalgrass suppression, which resulted in a competitive advantage for desirable recolonizing native plants.    




POTENTIAL FOR SPREAD AND CONTROL OF WESTERN MILFOIL (MRYIOPHYLLUM HIPPUROIDES) IN WESTERN US CANALS. L. W. Anderson*; USDA-ARS, Davis, CA (199)

ABSTRACT

The native submersed plant Myriophyllum hippuroides (Western milfoil) has infested large areas in the Friant-Kern Canal (Central California), a critically important irrigation and potable water delivery canal in Central California that carries water over 150miles.  Little published information on the growth of M. hippuroides is available.  Growth under varying irradiance (PAR) from 20 to 400 µmols/m2/sec and in rapidly flowing canals suggest that M. hippuriodes, though a native in N. America, has the capacity produce problematic biomass that can interfere with water delivery for crops, domestic and industrial uses.   Biomass of 400 g to 800 g/ m2 (dry wt) was obtained in late summer in the Friant-Kern Canal.  It's ability to root from small fragments in flowing systems also suggest that it can spread rapidly downstream once established.  Herbicide efficacy testing in mesocosms showed that M. hippuroides is suceptible to in-water applictions of triclopyr, endothall and fluridione at mid- to maximum label rates (i.e. concentrations in water of 1.0 to 2.5 ppm).  Simulated drawdown (dewatered conditions), followed by sediment- applied fluridone or penoxsulm suggest that this water management approach may provide control as well.   However, the extent and duration (viability) of the seed bank in infested sitesis not known.  The ability of M. hippuroides to grow under extremel low light (20µmols/m2/sec) indicates that management through reduction in ambient light (e.g. deepening canal sections) will not control the growth and spread of M. hippuroides and that other methods, such as aquatic herbicides and drawdown, or integrated methods should be investigated in field sites.



THE LIFE HISTORY OF COMMON REED: PHRAGMITES AUSTRALIS (CAV.) TRIN. EX STEUD. J. C. Cheshier*, J. D. Madsen, R. M. Wersal; Mississippi State University, Starkville, MS (200)

ABSTRACT

Common reed (Phragmites australis) is a non-native invasive perennial grass that is problematic in aquatic and riparian environments across the United States. The ability to reproduce quickly combined with its ability to cycle nutrients has made common reed an aggressive invader of aquatic environments.  Common reed often forms monotypic stands that displace native vegetation which provide food and cover for wildlife.  In order to help maintain native habitats and manage populations of common reed in the United States, an understanding of its life history and starch allocation patterns are needed.  Using a 0.1 m2 quadrat, twelve biomass samples were taken from four sites in the Mobile River delta in southern Alabama every month from January to December in 2006 and 2007.    Samples were separated into above and belowground biomass dried and weighed.  Starch allocation was determined using the STA20 starch assay kit.  Total biomass of common reed was greater in 2006 than in 2007 (t = 11.1, d.f. = 71, p<0.01).  As temperature decreased common reed biomass, both aboveground (p=0.05) and belowground (p<0.01), decreased.  Maximum aboveground biomass was 2200 ± 220 g m-2 in October of 2006 and 1302 ± 88 g m-2 in December of 2007.  Maximum belowground biomass was seen in November of 2006 and 2007 with 1602 ± 233 and 1610 ± 517 g m-2 respectively.  As aboveground biomass senesces, belowground biomass increases, resulting in a shift in biomass production.  Starch allocation in common reed followed biomass allocation, and declined with declining temperatures in both above and belowground tissues.  Aboveground starch allocation was highest in August of 2006 and December of 2007, 107 ± 0.8 and 129 ± 29 g starch m-2 respectively.  Belowground starch peaked at 236 ± 1.0 g starch m-2 during December of 2006 and 329 ± 0.5 g starch m-2 in November of 2007.  Application of management should be applied from March to July to exploit the low concentrations of starch in both above and belowground tissues of common reed.  Understanding the life history and starch allocation patterns of common reed has provided information to guide management strategies by identifying the vulnerable points in biomass and starch reserves in common reed. 




ECOLOGICAL DETERMINANTS OF INVASION BY SAHARA MUSTARD IN SOUTHWEST DESERTS. J. S. Holt*; University of California, Riverside, CA (201)

ABSTRACT

B. tournefortii (Sahara mustard), Brassica nigra (black mustard), and Hirschfeldia incana (shortpod mustard) are dominant, closely related non-native species that have overlapping, but dissimilar, niche distributions.  Sahara mustard is rapidly spreading in warm deserts of the southwest, while black and shortpod mustard are primarily limited to coastal regions.  We compared traits of Sahara mustard that might confer invasiveness in deserts with those of the two related species that have not invaded desert ecosystems, using controlled experiments conducted outdoors in a non-desert site (Riverside, CA) and a desert site (Blue Diamond, NV), and in greenhouses, over three years.  Desert and coastal Sahara mustard populations were also compared to determine whether locally adapted ecotypes are a cause of desert invasion.  There was no evidence for Sahara mustard ecotypes, but this species had a more rapid phenology than black and shortpod mustard under all experimental conditions, allowing it to reproduce under variable, stressful conditions such as deserts.  Although more successful in milder, mesic ecosystems, black and shortpod mustard may be limited by their ability to reproduce in the more arid desert niche.  Hand weeding Sahara mustard is currently the most common control method employed, but weeding is inadequate and expensive for managing large-scale invasions.  Rapid germination and phenology compared to natives may provide a window for selective control of exotic annuals immediately after exotic seedling emergence.  We tested the role of timing of control by comparing a cotyledon-stage glyphosate application to a bolting-stage application and to hand weeding Sahara mustard, plus an untreated check.  Treatments were tested at two sites dominated by either exotic or native annuals and followed for two years; early application was repeated the second year.  Early glyphosate application did not affect native cover, but did reduce exotic cover.  Late herbicide negatively impacted both exotics and natives.  Natives had little positive response, and then only through hand weeding under shrubs, but the same treatment caused an increase in the exotic E. cicutarium.  Results show that the rapid phenology of exotic annuals may be exploited to control exotics while minimizing impacts on natives in desert communities.  Jodie.holt@ucr.edu



EFFECTS OF NON-NATIVE EARTHWORMS ON THE SPREAD OF GARLIC MUSTARD (ALLIARIA PETIOLATA) IN INDIANA DECIDUOUS FORESTS. P. M. Quackenbush*, N. Emery, E. Kladivko, M. Jenkins, K. Gibson; Purdue University, West Lafayette, IN (202)

ABSTRACT

Earthworms, which are not native to forests in the Midwest region, have been associated with reduced native plant diversity in several studies and may facilitate plant invasions in Midwestern forests.  Garlic mustard is a common plant invader in eastern deciduous forests.  The invasion front for earthworms appears to be in the upper Midwest; however, relatively little is known about the distribution and impact of earthworms in states where they have long been present.  Six paired old and secondary growth forest stands (12 total stands) were sampled in 2009 and 2010.  Permanent transects (100 m long) were placed parallel to the forest edge in the interior and along the forest edge.  Percent cover and presence/absence data were recorded for herbaceous species within ten 1-m2 quadrats per transect in the spring.   Earthworms were collected in adjacent quadrats in the spring and fall by excavation and by pouring a mustard solution into the soil.  Earthworms were present at every site and in 73% of all quadrats.  Garlic mustard was not detected in 11 transects and more than half of all quadrats containing garlic mustard were found in just four transects.  Although 85% of quadrats containing garlic mustard also contained earthworms, this study suggests that the presence of earthworms alone is not sufficient to explain the current distribution of garlic mustard within Indiana forests.

 




THE EFFECT OF SPOTTED KNAPWEED, CENTAUREA MACULOSA, ON GERMINATION AND SURVIVAL OF THE RARE, THREATENED PITCHER’S THISTLE, CIRSIUM PITCHERI. S. M. Louda1, T. Rand2, K. Bradley3, K. K. Crider*4; 1University of Nebraska, Lincoln, NE, 2USDA-ARS, Sidney, MT, 3University of Nevada, Reno, NV, 4USDA Forest Service, Athens, GA (203)

ABSTRACT

Although invasive plants are a recognized threat to rare plants, direct data on the magnitude and type of their influence on the demography and population dynamics of rare species are uncommon. We performed a seed planting experiment to determine whether proximity to spotted knapweed (Centaurea maculosa), an invasive species, affected recruitment and survival of the federally threatened  Pitcher’s thistle (Cirsium pitcheri) in two characteristic thistle habitats – lakeshore linear dunes and high perched dunes – within Sleeping Bear Dunes National Lakeshore, Michigan, USA. The lakeshore linear dunes had lower surface soil moisture (0-15 cm depth), seedling emergence was very low (4 – 8%), and recruitment was lowest near a knapweed neighbor and tended to be higher in the open away from any neighbor. However, in the perched dune habitat with higher surface soil moisture, seedling emergence was much higher (13 26%), and proximity to another plant, a native species or knapweed, increased thistle emergence and establishment compared to out in the open. Thus, knapweed was either a competitor or a facilitator for seedling establishment by Pitcher’s thistle, depending on the local environment. Baby’s breath (Gypsophila paniculata) another exotic invasive species in the dune ecosystem, was significantly more abundant at the lakeshore linear dunes and may also have contributed to lower rates of thistle emergence and seedling establishment there.  Over time, neighbor effects changed to consistently negative for the survival of juvenile stage plants at both sites, and the negative effect was stronger for the knapweed neighbor than for the native neighbors. Paradoxically, water stress level of established juvenile thistle plants, quantified using isotopic analysis, was actually higher in the perched dune habitat with higher surface water availability than in the lakeshore linear dunes. We infer that in lakeshore linear dunes low surface soil moisture reduced seedling success, while higher levels of subsurface water availability compared to the perched dunes increased the performance and survival probability of established, more deeply rooted juvenile plants. If so, then our results suggest that successive life stages of Pitcher’s thistle are more strongly limited by different physical parameters that vary based on environmental context. Overall, the combined results demonstrate that environmental context is a critical determinant of the direct impact of the invasive plant species on regeneration dynamics and demography of this rare species.

 




WEED CONTAMINANTS IN SEED AS A PATHWAY FOR MOVEMENT OF INVASIVE PLANTS. J. S. Conn*; USDA-ARS, Fairbanks, AK (204)

ABSTRACT

New invasive plant populations can arise by planting seed that are contaminated with seed of invasive plant species. Large quantities of grass seed, crop seed, bird seed and flower mixes are imported to Alaska and may be a conduit for the movement of invasive plant seeds into the state.  To determine the importance of this pathway, seed were obtained from Alaska stores and were sampled for weed seed contaminants.  The following number of exotic species were found:  65 species in grass seed, 41 species in crop seed, 170 species in bird seed, and 19 species in wildflower mixes. On a per pound basis, grass seed contained an average of 471 seeds and 3.5 species; crop seed contained an average of 1949 seeds and 5.9 species, and bird seed contained and average of 460 seeds and 8.6 species. The effects of grass seed, crop and bird seed type; grower; and supplier on numbers of exotic plant seed contaminants are examined.




INTEGRATING SYSTEMATICS AND INVASION BIOLOGY: A CASE STUDY FROM ANTIGONON LEPTOPUS. J. M. Burke*, A. DiTommaso; Cornell University, Ithaca, NY (205)

ABSTRACT

Integrating systematics and invasion biology: a case study from Antigonon leptopus (corallita). Janelle M. Burke* and Antonio DiTommaso, Cornell University, Ithaca, NY.

 

Systematic studies often involve large compilations of herbarium, morphological, and molecular data. These data can be valuable for the study of invasive biology. For example, label data from herbarium specimens can aid in mapping the history of spread of an invasive plant, and detailed locality data can even target areas of spread and help to delimit range expansions. Taxonomic work on a plant group can generate taxonomic keys to identify current and potentially invasive species within a larger group, and also provide information about morphological and molecular variation among invasive populations within a species. The species used for this study, Antigonon leptopus (corallita), is a pantropical invasive vine particularly problematic on islands. Label data from herbarium specimens were used to map the spread of invasive A. leptopus over time. These data show the history of corallita introduced as a garden ornamental, with subsequent naturalization and escape. The introduction across the tropics mostly occurred in the early twentieth century. Molecular data suggest introductions outside the native range were not from one seed source, as exemplified by the genetic variation found within one island locality. These data demonstrate how a systematic undertaking, with an emphasis on sampling of invasive populations, can advance our understanding of the biology and ecology of invasive plants. This work highlights the need for greater communication and collaboration between plant systematists and weed scientists. E-mail correspondence: J. Burke, jmb328@cornell.edu




STEM PROPAGULE ESCAPE POTENTIAL OF THE BIOENERGY CROPS MISCANTHUS X GIGANTEUS AND ARUNDO DONAX. J. Mann*1, J. N. Barney2, J. M. DiTomaso1; 1University of California, Davis, Davis, CA, 2Virginia Tech, Blacksburg, VA (206)

ABSTRACT

Miscanthus (Miscanthus giganteus), a C4 grass from Japan, is a leading candidate as a dedicated bioenergy feedstock due to its broad environmental tolerance, rapid growth rate, ability to grow in low production soils. However, these characteristics are shared by many invasive species, including giant reed (Arundo donax), a C3 grass from the Mediterranean region, which is an economically important invasive plant throughout California and the US southwest. Giant reed is also a candidate bioenergy crop targeted for the southeastern US. Sterility narrows the propagule source of both species to vegetative propagules carried out of bioenergy crop fields and deposited into safe sites. To quantify vegetative propagule production from aboveground plant material of miscanthus and giant reed we assessed stem node viability and performance of whole culms and culm fragments in potting medium and standing water. We collected miscanthus culms in spring, summer, fall, and winter from established fields, and giant reed culms from feral stands located <5km away. Treatments were composed of whole culms and culm fragments (whole culms separated into single node fragments) that were planted in soil or placed in standing water for eight weeks. Miscanthus whole culms and fragments produced shoots and roots in both soil and standing water during May, July, and September, but failed to produce shoots and roots in November. Similarly, giant reed produced shoots and roots in both soil and standing water in May, July, and September, but also in November. Numbers of surviving propagules (node with shoots or roots) varied between species and within treatments. The group of May miscanthus whole culms growing in water yielded the largest proportion of surviving propagules across all treatments with 48% of potential propagules (n=62 May, n=115 July, n=197 September) producing new shoots, while the September fragments growing in soil gave the smallest proportion with 8% viability. Giant reed growing in water was notably different than miscanthus across whole culm and culm fragments groups and time of year. The November fragments growing in water gave the highest proportion of surviving propagules with 86% of potential propagules (n=124 July, n=179 September) surviving, while the September whole culms in soil yielded the lowest proportion of viable nodes with 24%.  Miscanthus demonstrates the capacity for whole culms and fragments to generate new plants in environments with abundant water during spring and summer months. Therefore, precautions should be considered if living (green) culms are removed from fields and transported through habitats containing either open water or abundant soil moisture during summer months. Giant reed showed a remarkable increase in propagule generation and productivity in both summer and fall compared to miscanthus. Most importantly, giant reed produced robust plants from culms in winter when miscanthus had senesced, and presents a risk for unintentional introduction during the winter harvest period.




MOLECULAR GENOTYPING TO DISTINGUISH SUBSPECIES OF OPLISMENUS. L. J. Cseke*1, S. M. Talley2; 1UAHuntsville, Huntsville, AL, 2USDA, Fort Collins, CO (207)

ABSTRACT

We have developed a molecular genotyping method to help establish the identity of Oplismenus hirtellus ssp. undulatifolius (OHU), a shade tolerant grass that was recently discovered invading the forest understory in Maryland and aggressively spread to the state of Virginia. Until recently, the origin of OHU, its genetic relatedness to our native (O. hirtellus ssp. setarius and fascicularis) and introduced ornamental (O. hirtellus ssp. varigatus) taxa, and how it entered the U.S. was unknown but critical to preventing its reintroduction and spread. Our molecular genotyping method provides a highly reliable and cost-effective diagnostic tool to accurately differentiate between OHU and closely related taxa, thus overcoming difficulties associated with polymorphic subspecies and discrepancies in the taxonomic treatment of Oplismenus.  Since misidentifications have already led to misdirected eradication procedures on native O. hirtellus subspecies in areas where this plant is rare, this method helps to prevent such misidentification. The methods were developed to work with the minimum amount of effort required to make an accurate distinction between the different subspecies and varieties, and they make use of differences in the nucleic acid sequences of the nuclear ITS region and/or plastid trnL-F region. DNA is extracted from a small tissue sample (1-100 mg of leaf, seed or root), and PCR is performed to amplify the desired DNA region. This is followed by direct PCR product sequencing using a single sequencing reaction that targets the sequence differences that can distinguish each subspecies from the others.  This method has also been used to test Oplismenus undulatifolius samples from Russia (Krasnodarskiy region), and the data indicate that this is a potential source population of OHU in the U.S.




A STUDY TO EVALUATE THE MORPHOLOGICAL AND SEED PERSISTENCE CHANGES ASSOCIATED WITH DOMESTICATION OF COW COCKLE GENOTYPES (SAPONARIA VACCARIA .L). H. S. Duddu*; University of Saskatchewan, Saskatoon, SK (208)

ABSTRACT




ENDODORMANCY RELEASE IN CROWN BUDS OF LEAFY SPURGE INVOLVES OVERLAPPING MOLECULAR NETWORKS RESPONSIVE TO ABIOTIC STRESS. M. Dogramaci*1, M. J. Christoffers2, D. P. Horvath1, J. V. Anderson1; 1USDA-ARS, Fargo, ND, 2North Dakota State University, Fargo, ND (209)

ABSTRACT

Vegetative reproduction in leafy spurge occurs from an abundance of underground adventitious buds (UABs) that exhibit well-defined phases of seasonal dormancy, which make this herbaceous perennial weed a model system for the study of bud dormancy. Since dormancy is a key factor allowing UABs of leafy spurge to survive and regenerate new shoots following extreme environmental fluctuations, an objective of this study was to understand the effects that cold- and dehydration-stress have on vegetative reproduction, flowering competence, and associated transcript profiles in endodormant crown buds. Vegetative growth and flowering potential of cold- and dehydration-stressed endodormant crown buds was monitored by removing the aerial portion of plants and watering the root system. Further, microarray analysis was used to follow transcriptome profiles and to identify critical signalling-pathways associated with endodormancy maintenance in crown buds. Surprisingly, only 3-days of dehydration-stress were required to break the endodormant phase, but new shoots were not flower competent. Since previous studies established that release of endodormancy and initiation of flowering competence in leafy spurge crown buds requires vernalizing cold, breaking of endodormancy via dehydration-stress, without floral induction, opens a unique approach to dissect these two molecular mechanisms independently. Breaking endodormancy by cold- and dehydration-stress identified LEC1, Photosystem I RC, and brassinosteroids as overlapping hubs of up-regulated genes, and DREB1A, CBF2, GPA1, MYC2, BHLH, BZIP, and flavonoids as overlapping hubs of down-regulated genes. Additionally, key genes involved in metabolic activity, chromatin modification, and cross-talk between growth regulators were identified as playing a role in endodormancy maintenance.




INTERGENERIC TRANSGENIC HYBRID IN THE BENTGRASS COMPLEX PRODUCED IN SITU. M. L. Zapiola*1, C. Mallory-Smith2; 1Universidad Católica Argentina, Buenos Aires, Argentina, 2Oregon State University, Corvallis, OR (210)

ABSTRACT

Creeping bentgrass (Agrostis stolonifera L.), a perennial, wind pollinated, outcrossing turfgrass species widely used on golf courses, has been genetically engineered to be resistant to glyphosate. Creeping bentgrass is part of a complex of compatible species that coexist in several environments. Hybridization among species in the complex is known to occur and creeping bentgrass and the annual species rabbitfoot grass (Polypogon monspeliensis (L.) Desf.) are known to produce intergeneric hybrids. Transgenic glyphosate-resistant creeping bentgrass (GRCB) was planted in 2002 within a control area in central Oregon, USA. Among the cross compatible feral species established in the area is rabbitfoot grass. We conducted a gene flow study at the landscape level to determine movement of the transgene. One of the objectives of this gene flow study was to determine the occurrence of spontaneous hybridization (i.e. natural, unassisted sexual reproduction between taxa in the field). During the greenhouse screening of seeds collected within and around the control area, we found a seedling that was transgenic but had an unusual phenotype. The seedling’s maternal plant was a transgenic creeping bentgrass. We hypothesized that the unusual looking seedling was a GRCB x rabbitfoot grass intergeneric hybrid. The seedling, along with seven transgenic half siblings, were studied further. In order to confirm our hypothesis we used a matK marker, chloroplast and nuclear SSRs, and sequenced the nuclear ITS. The chloroplast SSR and matK markers we developed confirmed that the putative hybrid had a creeping bentgrass chloroplast genome. The nuclear SSRs analysis placed the intergeneric hybrid in the rabbitfoot grass group. Of the seven ITS clones sequenced, two have sequences comparable to those of creeping bentgrass and five grouped with rabbitfoot grass ones confirming the finding of the first intergeneric hybrid produced in situ with a still USDA-regulated transgenic event.



USE OF AFLP MARKERS TO ASSESS GENETIC DIVERSITY IN PALMER AMARANTH (AMARANTHUS PALMERI) POPULATIONS FROM NORTH CAROLINA AND GEORGIA. A. Chandi*1, S. Mila-Lewis1, D. L. Jordan1, J. D. Burton1, A. York1, J. Whitaker2, A. S. Culpepper3; 1North Carolina State University, Raleigh, NC, 2University of Georgia, Statesboro, GA, 3University of Georgia, Tifton, GA (211)

ABSTRACT

Use of AFLP Markers to Assess Genetic Diversity in Palmer Amaranth (Amaranthus palmeri S. Wats.) Populations from North Carolina and Georgia. Chandi Aman *, Susana Mila-Lewis, David L. Jordan, Jim D. Burton, Alan York, Jared Whitaker¥ and Alfred S. Culpepper¥¥

ABSTRACT

Palmer amaranth has become one of the most troublesome weeds in southern cropping systems. This weed has confirmed resistance to herbicides representing four different modes of action including glycines, acetolactate syntahse inhibitors, dinitroanilines and photosystem II inhibitors representing different modes of action. Among other factors, development of herbicide resistance can be attributed to genetic diversity of the weed species. A great degree of phenotypic variation is observed in Palmer amaranth populations with respect to susceptibility to herbicides and plant growth and development  in general. These might be related to levels of genetic diversity existing in these populations. Research was conducted to assess genetic diversity among and within eight Palmer amaranth populations collected from North Carolina and Georgia using Amplified Fragment Length Polymorphism (AFLP) markers. Levels of genetic diversity were found to be high, ranging in value from 0.0773-0.8605. The highest and the lowest genetic similarities within populations were 0.5596 and 0.3569 for Crisp and Sumter counties in Georgia (both susceptible to glyphosate). Cluster and Principal Coordinate analyses grouped individuals mostly by geographic origin irrespective of either resistance or susceptibility to glyphosate or gender of individuals. Analysis of Molecular Variance results when populations were nested within states revealed that significant variation (P 0.001) existed among and within populations within states while variation among states was not significant (P = 0.372). Variation among and within populations within state accounted for 19% and 77% of the total variation, respectively. Variation among states accounted for only 3% of the total variation. The within population contribution towards total variation was always higher than among states and among populations within states irrespective of either resistance or susceptibility to glyphosate or gender of individuals. These results suggest that genetic variation in the studied populations is not discrete and cannot be accounted for by classification of individuals by state, response to glyphosate, or gender.

North Carolina State University Raleigh,

 ¥ University of Georgia, Tifton

¥¥ University of Georgia, Statesboro




MOLECULAR GENOTYPING WITHIN THE MIKANIA SPECIES COMPLEX. L. J. Cseke*1, S. M. Talley2; 1UAHuntsville, Huntsville, AL, 2USDA, Fort Collins, CO (212)

ABSTRACT

We have developed methods to provide a reliable and cost-effective diagnostic tool to differentiate between the highly invasive weed, Mikania micrantha and closely related species, including U.S. native species (M. scandens and M. cordifolia) and invasive species (M. cordata).  M. micrantha is a listed Federal Noxious Weed in the U. S. and a state noxious weed in ten states. Until recently, it has been successfully excluded from the U.S., but in late 2009, M. micrantha was found invading in Miami-Dade County, Florida. Taxonomists at the time had difficulties distinguishing it from the more wide spread M. scandens, and disagreements on its identification continue to present problems. We developed these methods to work with the minimum amount of effort required to make an accurate distinction among the different Mikania species by using differences in the nucleic acid sequences in the nuclear ITS region. The basic protocol involves extracting DNA from a small tissue sample (1-20 mg of dry leaf or herbarium specimens) followed by amplifying the ITS region with PCR. The PCR product is then sequenced using a single sequencing reaction with a specific sequencing primer. Comparison of the generated sequences with known orthologous sequences can then be performed to identify the species. Using these methods, we were able to confirm the identity of the suspect plants as M. micrantha, and the State of Florida took official action to eradicate it and has quarantined infected nurseries.



INFERRING THE ORIGINS AND SPREAD OF AGRICULTURAL WEEDS AND INVASIVE PLANTS USING MOLECULAR TOOLS. M. Jasieniuk*; University of California, Davis, Davis, CA (213)

ABSTRACT

The ability to detect population structure and infer the origins and introduction histories of weed invasions from neutral genetic variation has improved markedly due to advances in molecular and analytical methods.  I will briefly describe some novel approaches my lab has used to infer the origins and invasive spread of several weed species differing in reproductive mode, mating system, and ploidy.  The species include Italian ryegrass (Lolium multiflorum), pampas grass (Cortaderia selloana), jubata grass (Cortaderia jubata), invasive blackberries (Rubus spp.), invasive brooms (Cytisus-Genista complex), and water primroses (Ludwigia hexapetala and L. grandiflora).  Implications of the research results for understanding the processes underlying successful weed invasions, and for improving weed management and prevention programs will also be discussed.




DO WHITE-TAILED DEER AFFECT PLANT INVASION?: INSIGHTS FROM A META-ANALYSIS. K. M. Averill*, D. A. Mortensen; The Pennsylvania State University, University Park, PA (214)

ABSTRACT

Multiple factors influence the susceptibility of a forest to plant invasion, including propagule pressure, habitat fragmentation, and herbivory. The effect of white-tailed deer (Odocoileus virginianus) on plant invasion is unclear from current literature. In this collaborative project, a group of researchers contributed complete species data sets yielding over 400 plots across 12 sites. We used data from these paired deer exclosure and control plots to examine the effects of deer browsing on invasive plant species richness and abundance across the Mid-Atlantic region in the US. Among those sites with invasive plant presence, preliminary evidence suggests deer browsing promotes the invasion of some exotic species, including Microstegium vimineum and Polygonum cespitosum. On the other hand, exotic species with fleshy fruits, such as Lonicera japonica and Rosa multiflora, were more abundant in plots without deer. We found greater plant invasion in forests surrounded by a highly fragmented landscape than in forests located in remote and contiguous forests. Preliminary results reveal that deer exclosures impact plant invasion in a species- and context-dependent fashion.




SECONDARY SEED DISPERSAL BY VEHICLES: SIMULATING COLONIZATION ON A HETEROGENEOUS LANDSCAPE. L. J. Rew*, A. Wing, K. Taylor, B. D. Maxwell; Montana State University, Bozeman, MT (215)

ABSTRACT

The importance of secondary dispersal of seed by vehicles is often assumed but little quantified.  We completed a controlled experiment measuring seed loss from a vehicle and used these data in a simulation model to evaluate dispersal over space and time on a heterogeneous landscape.  In the controlled seed loss experiment we placed a known amount of seed and soil slurry onto steel plates that were then dried and attached to the chassis of a vehicle.  The vehicle was driven set distances on paved and unpaved road surfaces under wet and dry conditions after which the plates were removed and number of remaining seeds quantified.  Three different locations on the vehicle were assessed: bumpers, wheel wells and underside.  These data plus data for the whole vehicle were modeled using seven different long distance dispersal functions.  Overall, more seed were dispersed under wet conditions than dry, and on unpaved than paved roads.  The best fit dispersal function for each of the four different road surface/conditions were included in a cellular automata model with spatially heterogeneous landscape. In addition to basic population dynamics parameters (including reproduction and transition rates between seedbank and flowering plants), the model had a spatial component where dispersed seed survival was a function of environmental suitability.  The underlying landscape had a linear feature (road) horizontally dissecting the 7 cell x 3000 cell landscape, with the most suitable habitat located along the road.  Cell size represented 1 km2.  While the details of the model results cannot be fully explained here, the model does demonstrate the importance of understanding secondary dispersal by vehicles in addition to environmental suitability for successfully predicting invasions. This empirical and simulation exercise has provided an improved understanding of the rate of seed loss, and distance and shape of vehicular secondary seed dispersal curves which could help guide survey methods for newly invading species and development of prevention protocols. 

 




INTRA- AND INTER-SPECIFIC COMPETITION AMONG INVASIVE AND NATIVE SPECIES DURING EARLY STAGES OF PLANT GROWTH. S. Mangla*1, R. L. Sheley2, J. J. James2, S. R. Radosevich1; 1Oregon State University, Corvallis, OR, 2Oregon State University, Burns, OR (216)

ABSTRACT

Plant competition is an ecological process limiting grassland restoration success. Appropriate restoration techniques require an understanding of the degree to which intra- and inter-specific competition control invasive and native plant growth. The objective of this study was to determine how the intensity of intra- and inter-specific competition changes during early stages of plant growth. Two invasive (Bromus tectorum L. and Taeniatherum caput-medusae L. Nevski) and two native (Pseudoroegneria spicata (Pursh) A and Poa secunda J. Presl) species were grown in a diallel competition experiment, either alone or in 1:1 binary combinations and exposed to two levels of N (no N or 400 mg N·kg-1 soil added) in a greenhouse. Total biomass for each species was quantified over four harvests and competitive effects were calculated. Our results show that the relative magnitude of intra- and inter-specific competition changes through time. Intra-specific competition was intense for native species at the initial harvests and therefore important in contributing to the outcome of final size of native species seedlings. Interestingly, bluebunch wheatgrass imposed inter-specific competition on annual grasses at the first two harvests and appeared to be a better competitor than Sandberg’s bluegrass. We found that fast growing invasive species became more competitive compared to slow growing native species with increasing N and appear to establish a positive feedback mechanism between size and resource uptake. Opportunities to improve restoration success exist from determining the optimum combination of density, species proportion, and their spatial arrangement in various ecosystems and environments.




NONTOXIC ROLES OF POLYPHENOLS IN FACILITATING PLANT INVASIONS: CASE STUDY WITH JAPANESE KNOTWEED (POLYGONUM CUSPIDATUM). N. Tharayil*1, S. Nirmalkumar1, D. Triebwasser1, P. Alpert2, P. C. Bhowmik2; 1Clemson University, Clemson, SC, 2University of Massachusetts, Amherst, MA (217)

ABSTRACT

Polyphenols represent a diverse and the most abundant class of plant secondary compounds, and consists of chemically inert lignins and biologically reactive phenolic and flavonoid compounds. Traditionally, polyphenolic compounds have been implicated in many toxic plant-to-plant interactions that result in plant invasions.  Apart from the direct toxicity, polyphenols also play an important role in many ecosystem processes including soil nutrient cycling and organic matter decomposition. However, the effect of these compounds on such ecosystem processes in the invaded habitats is less understood. Japanese knotweed (Polygonum cuspidatum) is a secondary metabolite-rich noxious weed that invades diverse ecosystems across Europe and North America. We investigated the soil polyphenol profiles and the associated changes in soil processes in five knotweed invaded and adjacent non-invaded sites across eastern United States.

Physicochemical composition of plant litter and topsoil was assessed using Fourier Transform Infrared Spectrometry (FTIR). We used liquid chromatography coupled with tandem mass spectrometry analysis (HPLC-QToF) to characterize polyphenolic compounds in knotweed tissues and topsoils. We followed the degradation pattern of these compounds in the knotweed litter using field decomposition experiment and lab incubation assays.  We measured the activity of various carbon and nitrogen mineralizing enzymes in soil and decomposing litter to assess the alterations in microbial functional activity induced by knotweed litter quality.

FTIR analysis demonstrated a higher concentration of recalcitrant compounds (cuticle and polymeric-phenols) in knotweed litter and in invaded soils. Knotweed litter had a higher concentration of both flavonoid aglycons and glycosides, which accounted for 1% of leaf litter by dry-weight. However, all flavonoid compounds degraded rapidly both under field and lab incubation studies. Invaded soils had a high concentration of ester-linked phenolic acids, however, none of the flavonoids were present in invaded soils in detectable quantities. Knotweed tannins were primarily composed of proanthocyanidins (PC), and accounted for 10-15% of the leaf dry weight. More than 50% of the PC was fiber bound, resulting in a reduced rate of litter decomposition, and an increase in fungal-to-bacterial ratios in invaded sites. The high polyphenol content resulted in a seasonal variation of microbial enzyme activities in the soil and in the litter, between the invaded and the adjacent non-invaded sites. The influence of knotweed polyphenols on soil nutrient cycling was also seasonal. Our overall results suggest that, the presence of polyphenol compounds provides a less conducive microclimate for the microbial decomposer community, thus resulting in the accumulation of knotweed detritus, which in turn could smother the emergence of native species. 




PARASITIC WEEDS - A WORLD CHALLENGE. C. Parker*; Retired, Long Ashton Research Station, Bristol, England (218)

ABSTRACT

 PARASITIC WEEDS – A WORLD CHALLENGE

Species of Orobanche and Striga are the most damaging parasitic weed species worldwide. Their distribution, host range and economic importance will be reviewed. Overall, many million hectares are infested and losses amount to $US billions annually and there is little evidence of widescale reductions in intensity or losses caused, over the past years. Any successes in reducing their importance is generally sporadic and localised. In particular, Striga species on cereals continue to become more serious in many African countries owing to continued loss of soil fertility. There are also continuing risks of spread of both groups of parasite to new areas. Some other root hemi-parasites related to Striga are of concern, mainly in Africa, while the shoot-parasitic mistletoes and dodders will also be discussed. The dwarf mistletoes, Arceuthobium species, continue to cause major losses to forestry in N. America, while the dodders (Cuscuta species) are localized pests of a range of crops across many continents.




OVERVIEW OF METHODS DEVELOPMENT SUPPORT FOR THE USDA-CAROLINAS WITCHWEED ERADICATION PROGRAM - 1959-1995. R. G. Westbrooks*1, R. Eplee2, M. Langston2; 1Southeastern Community College, Whiteville, NC, 2USDA APHIS, Retired, Whiteville, NC (219)

ABSTRACT

The dramatic success of the federal/state program that has reduced the infestation of witchweed [Striga asiatica (L.) O. Kuntze] in the United States from 432,000+ acres in North Carolina and South Carolina in 1970, to less than 2,000 acres in North Carolina in 2010, is a testament to the agencies and the personnel who have worked tirelessly over the past 54 years to eliminate it. The knowledge that has made witchweed eradication in the United States a practical reality is a tribute to a number of prominent weed scientists who worked from the inception of the program in 1957 until 1995 to understand the parasite/host relationship and developed methods to control it. In 1995, most of the responsibility for field operations in the program was assumed to the North Carolina Department of Agriculture and Consumer Services. At that same time, the USDA APHIS Methods Development Center in Whiteville, North Carolina – the center of innovation in the Witchweed program, was closed. During that 38 year time span, program and cooperating scientists made tremendous advances in our understanding of witchweed taxonomy, biology, physiology, haustorial development, requirements for germination, effect of the environment on witchweed growth and development, movement and survival of witchweed seeds in the soil, and the potential ecological range in the United States. Also during this time period, the Witchweed Program Methods Development Group used this ever expanding knowledge base to develop and integrate effective survey and control methods and equipment into the Witchweed Field Program. This included ongoing field evaluations of all commercially available herbicides for witchweed control, development of cultural methods for witchweed control (e.g., use of trap crops such as cotton to induce suicidal germination of witchweed seeds in the soil), development of ethylene gas as a germination stimulant, and development of soil fumigants (e.g., methyl bromide and basamid) to devitalize witchweed seeds in the soil. This group also designed, built, and maintained most of the specialized application equipment that was used in the program, as well as soil sampling equipment and equipment to separate witchweed seeds from the soil. Since the Witchweed Program is nearing its long term goal of eradicating this parasite from the United States, it is clear that the tools, methods, and approaches that were developed by program scientists and other from 1957 until 1995 played a major role in the success of the effort. Unfortunately, the job is not yet finished, and the program faces new challenges, such as the lack of an approved fumigant to devitalize witchweed seeds in the soil. The urgent need for new methods to spot treat small infestations of witchweed that were traditionally fumigated with methyl bromide or granular basamid highlights the importance of science and technical support to a program of this magnitude and scope. Without such ongoing support, the Witchweed Program faces a protracted and uncertain future. It is fortunate that other more basic control methods that were developed for the program have withstood the test of time and are still available to help complete the task at hand.



CURRENT ERADICATION PROGRAM FOR THE WITCHWEED INFESTATION IN THE US. R. Iverson*; NC Dept Ag & Consumer Serv., Raleigh, NC (220)

ABSTRACT

Current Eradication Program for the Witchweed (Striga asiatica) Infestation in the United States.  Richard D. Iverson, North Carolina Dept. of Agriculture & Consumer Services, Raleigh, NC.

 

Witchweed, an obligate parasite of corn, sorghum and other grasses was first detected in North Carolina in Robeson County in 1955 but may have been present in other southeastern North Carolina counties and neighboring South Carolina counties as early as 1950.  The infestation in the Carolinas is the only known occurrence in the Western Hemisphere.  It is listed as a Federal/State Noxious Weed and at one time had infested more than 433,000 acres in the Carolinas including as many as 27 counties in North Carolina. Combined state/federal quarantines were invoked against witchweed in 1957. Components of the witchweed eradication program include management of quarantine areas to prevent its spread, a programmed schedule of surveys, and the application of control methods to eliminate witchweed or deny witchweed reproduction.  The most common control methods include soil fumigation with methyl bromide, glyphosate application, hand pulling, disking, and soil injection of ethylene gas to encourage witchweed germination and depletion of seed in the soil.  Surveys are done to delimit infested area boundaries, detect new infestations, evaluate treatment effectiveness, and confirm successful eradication before acres can be terminated and removed from the program.  Through the combined efforts of state and federal agricultural agencies, landowners and farm managers over the last 50 years, the quarantine areas have been reduced to portions of only 5 counties in North Carolina.  The last infested acre in South Carolina was released from quarantine in 2009. The amount of infested acreage has been reduced by over 99% since the start of the program to less than 1,900 acres at the end of 2010.  Survey for witchweed is still completed by the U.S. Dept. of Agriculture, Animal and Plant Health Inspection Service, Plant Pest Quarantine (USDA, APHIS ,PPQ) in South Carolina and the USDA, APHIS, PPQ continues to provide support to NCDA&CS  through a cooperative agreement to eradicate remaining acres of witchweed in North Carolina.  The Carolinas witchweed eradication program demonstrates that weed eradication is possible through research, interagency and landowner cooperation, consistent annual financial support and persistence.




CURRENT PARASITIC WEED CONTROL METHODS DEVELOPMENT EFFORTS IN THE US. C. L. Ramsey*; USDA-APHIS, Fort Collins, CO (221)

ABSTRACT

Parasitic weed control includes Striga asiatica (witchweed) control in South Caronlina, Orobanche spp. (broomrape) control in the south, southeast, and northwest, and Cuscuta japonica (Japanese dodder) control in the south and western USA.  Witchweed control has included soil seed bank stimulants such as ethylene to induce suicidal seed germination.   Witch weed control also includes methyl bromide soil fumigation which is more expensive than ethylene treatments.  Broomrape control in the USA is usually limited to post emergence control with selective herbicides, or “host denial” which includes the use of broadleaf herbicides for turf grass infestations. Japanese dodder is under “official control” regulations in California, which includes soil seed bank eradiation treatments with soil fumigants.  In general soil seed bank treatments with chemical biocides or fumigants offers the best control of parasitic weed seed banks, up to 95% control.  However, such soil treatments are typically expensive, and are under increasingly difficult and extensive EPA regulatory restrictions.  Most parasitic weed infestations in the USA are in natural areas, lawns, or major crops, which precludes the use of expensive soil fumigant applications.  The increasing regulatory and application costs of parasitic seed bank control may ultimately lead to reduced control efforts, or smaller agency control programs, that will contribute to the continued spread of these high risk, invasive weeds.

 

EPA registered soil fumigants/biocides used for weed control include: methyl bromide (restricted to quarantine uses), methyl iodide (Midas), dimethyl disulfide (Paladin), metam sodium or metam potassium (Vapam or K-Pam), and dazomet (Basamid).  The latter two soil biocides are applied as a liquid (Vapam) or as a granule (Basamid), and their chemical costs are about half to twenty times less expensive than methyl bromide or Midas.  These biocides do not require tarping and are relatively inexpensive, which may make them economical enough for use on non-specialty crops. Both Vapam and Basamid is converted to methyl isothiocyanate (MITC) by soil moisture, and their soil half-lives range from 6 days to 3-4 weeks depending on soil properties, microbial activity, and rainfall patterns.  Recent soil seed bank chemical treatment innovations such as triple fumigant mixes, water sealing, soil sealing/surface compaction, pre-irrigation or soil moisture monitoring, chemigation, solarization, and controlled release formulations may slow down chemical losses to volatilization, leaching, or biotic/abiotic degradation.  Soil seals could be created with clay deflocculant chemicals in sandy soils, or controlled release materials/formulations could be tested for reduced degradation losses in the seed zone of the soil.  Current research should be focused on soil biocides that do not require extensive regulatory practices, and are economical enough to be practical for parasitic weed infestations in low profit land uses.  Long term research should also continue with unregistered, nonfumigant soil biocides, chemical seed stimulants, trap crops, false crop hosts, genetically modified crop that are resistant to parasitic weed attachment, and herbicide resistant crops.    




OROBANCHE MINOR AND THE 3 R'S: REGULATION, RESEARCH, AND REALITY. C. Mallory-Smith*; Oregon State University, Corvallis, OR (222)

ABSTRACT

Small broomrape (Orobanche minor) was first identified in Oregon in 1923.  Between 1923 and 1997 there were only six reports of the species in Oregon.  Small broomrape is a holoparasitic weed that attaches to the root of its host and can lead to crop failure depending on the level of infestation.  Small broomrape was identified in a red clover field in Oregon in 1998. The Oregon Department of Agriculture (ODA) was notified but because the species was not included in the state’s noxious weed list there was no action plan in place for control of the species. There was a delay of one year before ODA took action and then it was in response to an inquiry from USDA-APHIS on what actions were being taken.  In September 1999, the ODA visited the site along with representatives of USDA-APHIS and Oregon State University (OSU) to evaluate potential actions.  The field was quarantined and the clover was destroyed by burning the field.  In 2000 and 2001, the ODA surveyed red and white clover fields in Oregon for the presence of clover broomrape; 15 infested fields were identified in 2000 and 22 in 2001.  In 2000, a quarantine was established for small broomrape in red clover seed.  Provisions of the quarantine required either a negative seed test for the presence of small broomrape seed or that seed cleaning incorporated particular processes.  The quarantine also required that screenings from seed lots with small broomrape be disposed of in a manner that would devitalize any seeds.  In 2003, the ODA amended the quarantine to eliminate the mandatory seed sampling and testing.  It also eliminated the requirement of reporting infested fields and seed lots. Presently, small broomrape is listed as a class “B” noxious weed in Oregon. Beginning in 1998, research studies were conducted by OSU for the management of clover broomrape. Studies included evaluating herbicides for its control, development of a growing degree model to predict its germination and emergence in relationship to clover development, and determining alternate hosts and false hosts. Imazamox was identified and registered for control of small broomrape in clover. Clover broomrape has a wide host range but false hosts were identified for use to reduce the seedbank. Clover broomrape was not eradicated and is still found in clover fields and has been reported on noncrop sites in Oregon.  The removal of the quarantine status and the mandatory reporting requirement eliminated any of chance for eradication or containment of this weed species in Oregon.




TECHNOLOGIES FOR PRECISION CONTROL OF OROBANCHE. H. Eizenberg*; Newe Ya’ar Research Center, Ramat Yishay, Israel (223)

ABSTRACT

Precision chemical control of the root parasites broomrapes (Orobanche or Phlipanche spp.), aims at applying the appropriate herbicide at the optimal rate and timing, only in the infested area. This approach is supported by the current advances in modeling and the availability of new technologies for weed detection and mapping. However, the detection of root parasites is complex, compared to non-parasitic weeds as it grows in the soil subsurface throughout the initial developmental stages when it is sensitive to herbicides. To address this difficulty, specific methodologies using advanced technologies were recently introduced, and will be presented in this abstract. The use of an in situ non destructive minirhyzotron video camera, to monitor the subsurface developmental stages of the parasite on the host root system allows development of a robust dynamic parasitism model, based on soil temperatures. Temperatures units can be




DOSE-RESPONSE: BACKGROUND AND PERSPECTIVES ON THE DEVELOPMENT OF ANALYSIS METHODOLOGY. S. S. Seefeldt*1, W. J. Price2, B. Shafii2; 1USDA-ARS, Fairbanks, AK, 2University of Idaho, Moscow, ID (224)

ABSTRACT

Understanding and modeling the response of a living organism to a dose of a chemical or biological compound is an important aspect of biologic science.  Many absorbed or ingested organic and inorganic components that are beneficial or at least harmless at low doses can be toxic at higher doses.  When trying to recommend doses of a substance for killing a weed without harming a crop, the responses of the two plant species must be predicted.  Early studies have determined that the response was often an asymmetric sigmoidal-shaped curve and that there was inherent variability in susceptibility among individuals in a population.  From 1930 until almost 1960 there were heated discussions concerning whether probit or logit functions were best for modeling dose-response relationships.  At that time all analyses had to be done by hand.  Several attempts were made to simplify the calculations through the use of specially designed graph paper, but adoption of these methods was limited.  Rather than spending large amounts of time with these models, most researchers resorted to conducting simpler average response analyses such as ANOVA at specific doses, or attempting to transform data into a linear format followed by linear regression.  None of these simplified methods were useful for describing the pattern of data at extreme doses nor were they biologically relevant.  With the advent of computers and statistical software, more complex and biologically relevant models could now be utilized to analyze dose-response relationships. The estimation procedures for these models are discussed and demonstrated in the upcoming presentations in this series.




ESTIMATION TECHNIQUES FOR DOSE-RESPONSE FUNCTIONS. B. Shafii*1, W. J. Price1, S. S. Seefeldt2; 1University of Idaho, Moscow, ID, 2USDA-ARS, Fairbanks, AK (225)

ABSTRACT

Dose-response design is often used in agricultural research when it is necessary to measure a biological response at various levels of an experimental factor.  As might be expected, this type of research is common in the biomedical and chemical fields, as well as in other disciplines such as plant, animal, soil and environmental sciences. Additionally, the dose-response curve can be used to determine an unknown dosage. This type of calibration problem forms the basis for bioassay analysis and is useful when observed responses are available, but their associated dosages are unknown. Traditional statistical approaches to estimation of dose-response percentiles and the bioassay problem have relied on inverted solutions and approximations. While theoretical improvements for both estimation and calibration have been long known, the means and methods to practically implement the required computations have been prohibitive. Recent advances in computer hardware and software, however, have brought these improvements within reach of agricultural researchers. Development and application of these newer methods will provide a wider range of options and better solution accuracy to the dose-response problem.  This presentation examines both the traditional and modern approaches to estimation and calibration of dose-response functions. Empirical demonstration of these techniques will be covered as part of the next presentation in this series.



APPLIED DOSE-RESPONSE MODELS IN WEED SCIENCE. W. J. Price*1, B. Shafii1, S. S. Seefeldt2; 1University of Idaho, Moscow, ID, 2USDA-ARS, Fairbanks, AK (226)

ABSTRACT

In this presentation, estimation of dose-response curves, as covered in the previous talk, will be demonstrated using the SAS software system.  The topics addressed will encompass choosing an appropriate dose-response model, use of fixed and random model components, handling of discrete versus continuous responses, and specification of statistical inferences utilizing contrasts of parameter estimates.  Further demonstration will be given for calibration curve development and the subsequent estimation of an unknown dose.   The SAS procedures used will include PROC NLIN, PROC NLMIXED, and PROC MCMC and will employ least squares, maximum likelihood and Bayesian estimation techniques.  The examples shown will be taken from a variety of weed science experiments and are designed to provide users with the tools necessary for carrying out dose-response analyses.  Some knowledge of the SAS system will be useful, but not strictly required.




EFFICACY OF LIQUID CO2 FOR WEED CONTROL IN TURFGRASS SYSTEMS. D. F. Lewis*, T. W. Gannon, M. D. Jeffries, F. H. Yelverton; North Carolina State University, Raleigh, NC (227)

ABSTRACT

Due to rising public concern with the environmental impact of herbicides, non-chemical weed control techniques have increased in popularity.  Typical ‘organic’ crop production utilizes mechanical weed control, including soil cultivation, flaming, and hand-weeding, among other techniques.  However, these mechanisms are not applicable in turfgrass settings due to their destructive nature or high labor cost, leading many turfgrass managers with limited alternatives to herbicides.  The formation of a frost-like layer has been observed on plant tissue following liquid CO2 applications.  Depending on the duration and severity of tissue freezing, prolonged exposure to liquid CO2 may result in irreversible cellular destruction, interference of physiological processes, and eventual plant death.  Research was conducted in Raleigh, NC throughout 2010 to determine the efficacy of reclaimed liquid CO2 for weed control in turfgrass systems.  Liquid CO2 was applied utilizing a prototype handheld applicator equipped with an XR 8002 or XR 8004 nozzle calibrated to deliver 0.008 kg CO2 m-2sec-1 or 0.016 kg m-2 sec-1, respectively.  Treatments included incremental liquid CO2 exposure times (2-60 seconds) and comparative herbicide standards.  Common annual or perennial turf weed species, including annual bluegrass (Poa annua L.), buckhorn plantain (Plantago lanceolata L.), corn speedwell (Veronica arvensis L.), large crabgrass (Digitaria sanguinalis (L.) Scop.), smooth crabgrass (Digitaria ischaemum Schreb. ex Muhl.), goosegrass (Eleusine indica (L.) Gaertn.), Virginia buttonweed (Diodia virginiana L.), and white clover (Trifolium repens L.), were evaluated under greenhouse and/or field conditions.  Weed species were visually rated for control on a 0-100% scale (0=no visible plant injury; 100=complete plant death).  Results indicated greater weed control following prolonged exposure to liquid CO2 applications.  Annual weed species were more susceptible to liquid CO2 compared to perennial species; however, control varied depending on plant maturity.  Prototype modification reduced the LD50 of crabgrass (1-3 tiller growth stage) from 14.8 to 2.6 seconds.  While no formal turfgrass tolerance studies have been conducted to date, observations indicate common bermudagrass (Cynodon dactylon (L.) Pers.) and tall fescue (Festuca arundinacea Schreb.) tolerance to liquid CO2 applications.  These data suggest liquid CO2 applications may provide an alternative to synthetic herbicides for control of select weeds in turfgrass systems.




GROWING TURFGRASS WITHOUT CONVENTIONAL HERBICIDES: EXAMINING THE ROLE OF ALTERNATIVE STRATEGIES. C. Siva*, F. J. Tardif, G. Boland, K. S. Jordan; University of Guelph, Guelph, ON (228)

ABSTRACT

Dicot weeds such as dandelion (Taraxacum officinale Wigg.), are major pests of turfgrass, competing for space, light, and nutrients. Conventionally, chemical herbicides (e.g. glyphosate, 2, 4-D) have been used to manage these weeds. However, the Ontario Cosmetic Pesticide Ban implemented in 2009, restricts the use of these pesticides in urban settings. This has increased the demand for alternative weed management strategies. This study examines the effectiveness of various weed management treatments as potential alternatives to conventional herbicides for site-preparation and for the management of dicot weeds (post-renovation) in Ontario. The treatments are: untreated control, glyphosate (Roundup), acetic acid (EcoClear), and flame-weeding as site-preparation treatments and untreated control, 2,4-D/mecoprop/dicamba (Par III), chelated iron (Fiesta), lactic acid (Organo-Sol), Sclerotinia minor (Sarritor) and corn gluten meal as post-renovation treatments. Sod is also included as an additional, stand-alone treatment. Weed populations were assessed visually and using a point quadrat. Weed cover did not differ among site-preparation treatments. Plots treated with post-renovation treatments products have significantly different weed populations compared to those receiving conventional treatments such as glyphosate followed by 2,4-D. While some alternative options were more effective than others, the cost of applying sufficient product to gain desired effects may become quite expensive for a home lawn owner.




REDUCED CHEMICAL PROGRAMS FOR CRABGRASS CONTROL IN COOL SEASON TURF USING CORN GLUTEN MEAL. A. Smith*, S. Askew; Virginia Tech, Blacksburg, VA (229)

ABSTRACT

For homeowners and gardeners concerned with the environmental impact of herbicide use, corn gluten meal (CGM) has become a popular alternative for weed control. CGM is the by-product of corn processing and is used as a granular product for pre-emergent crabgrass control. Research has shown that partial weed control can be achieved at 975 kg/ha. For some, partial weed control is not sufficient and additional CGM is added, sometimes up to three applications of 975 kg/ha during the summer. Three applications of CGM equate to 263 kg N/ha, exceeding the recommended nitrogen requirements for turf by approximately 5.5 times. Excessive nitrogen is often a precursor for disease problems and can encourage weed growth where the turf stand is not competitive. To minimize the risk of nitrogen over-fertilization while improving weed control, experiments were initiated to evaluate the efficacy of applying CGM impregnated with 0.25 and 0.5 times label rates of pre-emergent herbicides on smooth crabgrass control. Normal label rates were 0.84 kg ai/ha for prodiamine, 1.1 kg ai/ha for pendimethalin, 2.2 kg ai/ha for oxadiazon, and 0.28 kg ai/ha for dithiopyr. Trials were established in two locations. Turf species were mature stands of tall fescue or Kentucky bluegrass. CGM was applied at 488 kg/ha once in a single application or at 244 kg/ha twice at a 1-month interval. CGM was impregnated with ¼ or ½ rates of dithiopyr, pendimethalin, prodiamine, or oxadiazon and applied as a granule in late April and May (for the split application). Split applications included split herbicide rates such that no more than the specified 0.25 or 0.5 times the labeled rate was applied in the season. Herbicides were also applied alone using sand as a granular carrier. Weed ratings, weed counts, and turf quality were rated during the season. Nontreated plots had 40% smooth crabgrass cover in August and CGM alone or most herbicides alone did not reduce cover. Nine treatments reduced crabgrass cover. When applied on a sand carrier, only prodiamine in a single application reduced crabgrass cover. The same treatment, carried on CGM, also reduced crabgrass cover. Pendimethalin (0.5x rate- single application) reduced crabgrass cover. Split applications of 0.5x dithiopyr, oxadiazon, and pendimethalin reduced cover. At 0.25x dithiopyr, in a split application, reduced crabgrass cover. These data suggest that several herbicides may be mixed with CGM to improve crabgrass control. Prodiamine mixed with CGM tended to provide the most consistent and highest numerical suppression of crabgrass, but only when applied in a single application. Dithiopyr and oxadiazon mixed with CGM preformed best when treatment was split into two applications, and pendimethalin worked as both single and split applications.         




DURATION OF PERENNIAL RYEGRASS COMPETITION AFFECTS BERMUDAGRASS QUALITY. B. McNulty*, T. Middlesteadt, S. Askew; Virginia Tech, Blacksburg, VA (230)

ABSTRACT

Bermudagrass (Cynodon dactylon) is a warm season, C-4, turfgrass that is commonly used on golf courses, athletic fields, and home lawns in the transition zone and southern climates. Bermudagrass enters a dormant period in the winter months turning the green tissue a light tan color. As a result, dormant bermudagrass is commonly overseeded with a cool season grass to provide a green surface for aesthetics as well as functionality and safety. The most common species used for this process is perennial ryegrass (Lolium perenne). Its speed of establishment, dark green color, and fine texture make it a desirable species for winter overseeding. Due to new varieties of perennial ryegrass that are more heat tolerant, spring transition back to bermudagrass has proven more difficult in recent years. Successful spring transition depends on climate, perennial ryegrass seeding rate, bermudagrass and perennial ryegrass cultivar, and management practices. Two studies were conducted in 2006, at the Glade Road Research Center (GRRC) and Turfgrass Research Center (TRC) in Blacksburg, VA. At the GRCC, ‘Patriot’ bermudagrass was utilized, while ‘Midiron’ bermudagrass was used at the TRC location. The study was repeated in 2007 at the Virginia Tech Golf Course (VTGC) on ‘Riviera’ bermudagrass in Blacksburg, VA. All treatments were arranged in a randomized complete block design with treatments replicated three times. All plots were 0.9 by 1.2 m and overseeded with perennial ryegrass at 275 kg/ha pure live seed in late September for the respective years. Foramsulfuron at 29 g ai/ha was applied weekly, for 24 weeks, starting April 6 using a CO2 pressurized backpack sprayer calibrated to deliver 280 L/ha. Ratings for all three trials included bermudagrass cover, biomass accumulation, and total nonstructural carbohydrate accumulation.  When averaged over trials, bermudagrass biomass was 792 g when under constant competition with perennial ryegrass and remained static for the first 100 heat units and then tended to increase, adding approximately 1 g biomass per heat unit for the next 200 heat units in a curvilinear fashion. Effects of competition-free heat units on bermudagrass biomass were similar to trends in bermudagrass cover. Although the cultivars exhibited similar responses of biomass production to cumulative growing degree days, the magnitude of biomass production by each cultivar varied. When averaged over treatments, biomass of 'Midiron', 'Patriot', and 'Riviera' was 495, 1081, and 1172 g/m2, respectively, with 'Patriot' and 'Riviera' statistically equivalent and greater than 'Midiron'. Our data suggest that the time of perennial ryegrass removal for optimum bermudagrass cover is a function of noncompetitive days of growth and the number of cumulative noncompetitive growing degree days. When large quantities of cumulative noncompetitive growing degree days are accumulated in a small number of days, a marginal number of noncompetitive growth days may still be necessary for acceptable bermudagrass cover. If noncompetitive days of growth are granted in a period of time in which cumulative noncompetitive growing degree days are being accumulated slowly, numerous days of noncompetitive growth may be necessary to reach acceptable bermudagrass cover. In addition, we determined that bermudagrass variety impacts the days of noncompetitive growth and cumulative noncompetitive growing degree days needed to obtain acceptable bermudagrass cover. More aggressive varieties of bermudagrass such as ‘Patriot’ may be able to outcompete perennial ryegrass and need less days of noncompetitive growth and cumulative noncompetitive growing degree days. Furthermore, it is possible that the number of cumulative noncompetitive growing degree days has more impact on bermudagrass biomass accumulation than cover. While increased cumulative noncompetitive growing degree days does not necessarily lead to more bermudagrass cover, it appears that it leads to more biomass accumulation, depending on variety. 




PARTIAL CONTROL: A NOVEL APPROACH TO SPRING TRANSITION OF OVERSEEDED BERMUDAGRASS. B. McNulty*, T. Middlesteadt, S. Askew; Virginia Tech, Blacksburg, VA (231)

ABSTRACT

Bermudagrass (Cynodon dactylon) is a warm season turfgrass that is commonly used in the transition zone and southern climates on golf courses, athletic fields, and home lawns. In winter months, bermudagrass goes dormant and turns from green to a light tan color. To remedy this problem, many turf managers overseed dormant bermudagrass with perennial ryegrass (Lolium perenne). Perennial ryegrass’ quick establishment, fine texture, and dark green color make it a desirable species for this application, but advances in varieties have made it more heat tolerant in recent years. This has made transitioning back to bermudagrass in warmer months difficult, warranting the use of selective herbicides to aid in the process. Timing of these products can be difficult and, if not done properly, could kill perennial ryegrass too quickly or not at all. Partial control of ryegrass, 20-40% treated, could prove beneficial in the slow transition from perennial ryegrass to bermudagrass. To investigate further, two trials were conducted, one in 2006 on ‘Vamont’ bermudagrass at Farmington Country Club (FCC) in Charlottesville, VA and the other in 2007 at the Virginia Tech Golf Course (VTGC) on ‘Riviera’ bermudagrass. Three partial control techniques were evaluated in these studies, drip, sponge, and strip. Custom equipment was constructed at the Glade Road Research Facility to accommodate all three techniques. All treatments were arranged in a randomized complete block design with 3 replications. Drip applicator was calibrated to deliver 1 drip every 10 cm (1,635 L/ha), while the sponge applicator was calibrated to deliver a 3-cm diameter sponge-dab every 10 cm (1,402 L/ha). Strip application (280 L/ha) was sprayed traditionally but using a custom constructed template to shield the turf not to be treated, while allowing strips of turf to receive the herbicide. Treatments included; foramsulfuron at 30% coverage applied early, trifloxysulfuron at 30% coverage applied early, foramsulfuron at 30% coverage applied early and late, and foramsulfuron at 20% coverage applied early and late. Non-treated checks with no partial treatment, were included in all trial locations. The FCC trial was initiated on April 26, 2006 and late treatments were applied on May 18, 2006. The VTGC trial was initiated on May 9, 2007 and late treatments were made on May 30, 2007. On July 7th of both years, a broadcast application of foramsulfuron was made to eliminate all remaining perennial ryegrass. Ratings included bermudagrass cover and quality. At FCC, strip application reduced bermudagrass quality to 4.9 and 5.3 at 22 and 50 days after treatment (DAT), respectively. Drip and sponge applications maintained turf quality greater than 7 throughout the transition process. All partial control techniques significantly improved turf quality when compared to the nontreated control at 86 DAT. In 2007 at VTGC, the same trends were visible. Strip application reduced turf quality early in the season, and at 63 DAT all partial control techniques significantly improved turfgrass quality when compared to the nontreated control.  For bermudagrass cover, all application techniques increased bermudagrass cover from 19% in nontreated plots to over 30% in partial control treated plots. At the time of foramsulfuron blanket application, non-treated plots had 40% bermudagrass cover, while all partial control plots had increased bermudagrass cover by 12-20%. These studies show that partial control techniques of perennial ryegrass in overseeded bermudagrass aid in the transition process and result in greater cover and quality of the desired turf species.              




MESOTRIONE TRANSLOCATION IN KENTUCKY BLUEGRASS AND ANNUAL BLUEGRASS. A. Post*1, M. Goddard2, S. Askew1; 1Virginia Tech, Blacksburg, VA, 2Monsanto, Scott, MS (232)

ABSTRACT

Mesotrione is a HPPD inhibiting herbicide newly registered for use in turfgrass in the United States in 2008. Registration includes pre- and postemergent broadleaf and grassy weed control in tall fescue, Kentucky bluegrass, centipedegrass, St. Augustinegrass, perennial ryegrass and fine fescue. It is particularly useful for controlling annual bluegrass in tolerant turf species.   The mechanisms of absorption and translocation of mesotrione are not well understood in turf, but interspecific differences in tolerance and selectivity have been noted even within genera. Marked differences in tolerance between Kentucky and annual bluegrass are particularly interesting. The objective of this research is to examine translocation of 14C-mesotrione in Kentucky bluegrass and annual bluegrass to characterize differences in their susceptibility to mesotrione. 

 

Trials were established in the greenhouse July 10th and September 16th 2009. They were arranged as a split-split plot design with six main plots of harvest timing (0.17, 4, 24, 48, 96, and 144 hours after treatment) and sub-plots of a 2 x 2 factorial containing two plant species (annual and Kentucky bluegrass) and two mesotrione application placements (foliar applied and root applied). The sub-sub plots included plant partitions for evaluation of translocation (treated foliage, treated root, non-treated foliage, non-treated roots, and root exudates). Whole plants were harvested at the given timings and divided into the described partitions for evaluation. 

 

In both studies, more 14C was absorbed when labeled mesotrione was applied to foliage than when applied to roots in both species. Recovery of 14C was also higher from treated foliage than treated roots in both species. Foliar absorbed 14C-mesotrione was more often translocated to other plant parts than root absorbed mesotrione. Root absorbed 14C –mesotrione was most often recovered from root exudates rather than other plant parts. In both trials annual bluegrass absorbed more 14C following mesotrione application than Kentucky bluegrass. Increased sensitivity of annual bluegrass to mesotrione when compared to Kentucky bluegrass may be due in part to differences in herbicide absorption. Further studies are planned to elucidate differences in 14C-Mesotrione metabolism rates between the two species.




PREEMERGENCE CONTROL OF PARTHENIUM HYSTEROPHORUS AND COMMELINA BENGHALENSIS. B. Stamps*; University of Florida/IFAS, Apopka, FL (233)

ABSTRACT

Preemergence control of Santa Maria feverfew (Parthenium hysterophorus L.) and jio (Commelina benghalensis).  Robert H. Stamps, Professor, University of Florida, IFAS, Mid-Florida Research and Education Center, Apopka

Santa Maria feverfew (a.k.a. parthenium weed, ragweed parthenium) is a Weed of National Significance in Australia, is considered by some to be one of the ten worst weeds in India and is becoming a more prevalent problem in Florida, USA.  Jio (a.k.a. Benghal dayflower) is listed as a noxious weed by several states and the United States government.  Jio is also becoming a more widespread plant in Florida.  Both of these weeds are easily spread during the shipment of ornamental plants and the presence of jio in ornamental plant nurseries is grounds for quarantining the nurseries.  After removal of established plants, both of these plants can recolonize the nurseries from seed.  Therefore, it is important to ascertain which preemergence herbicides have residual efficacy in preventing these weeds from reestablishing from seed.  From 2007 to 2010 studies were conducted to determine the efficacy of preemergence herbicides in controlling one or both of these weeds.  All studies were conducted under commercial containerized-plant production systems typical of ornamental plant nurseries in Florida.  Containers were filled with medium composed of pine bark:new peat:sand (6:4:1 by vol) and watered with overhead irrigation.  Weed seed were sown at 0 days after the treatments were applied (DAT), and again at 14, 28, or 56 DAT depending on the experiment.  Containers were fertilized with recommended rates of controlled-release fertilizer.  Treatments were also reapplied in some trials after the weed top growth was removed.  Weed control was determined by visual estimates made every two to four weeks and by the dry top weights of the harvested weeds.  When Santa Maria feverfew seeds were sown at 0 DAT, indaziflam at 4080 g a.i. ha1 was completely effective.  Flumioxazin (0.42 kg a.i. ha1), oxadiazon (3.36 g a.i. ha1), oxyfluorfen + oryzalin (2.24 + 1.12 g a.i. ha1), and oxyfluorfen + prodiamine (2.24 + 0.85 g a.i. ha1) provided 83 to essentially 100% control depending on treatment and trial.  Commercial herbicides containing combinations of dimethenamid-P + pendimethalin, trifluralin + isoxaben and trifluralin + isoxaben + oxyfluorfen were generally only effective at their higher label rates.  Dithiopyr (0.56 g a.i. ha1), oxadiazon + pendimethalin (2.24 + 1.4 g a.i. ha1), prodiamine (0.95 g a.i. ha1) and dimethenamid-P (0.841.68 g a.i. ha1) were not effective controlling Santa Maria feverfew.  In general, jio was less well controlled using preemergence herbicides than Santa Maria feverfew.  This may be due, in part, to slower germination over time of jio seeds allowing for more dissipation of herbicide concentrations at the medium surface.  Flumioxazin, oxyfluorfen + oryzalin or prodiamine, and prodiamine were the most effective treatments.  Dithiopyr, isoxaben, trifluralin + isoxaben (3.36 + 0.84 g a.i. ha1) and trifluralin + isoxaben + oxyfluorfen (3.36 + 0.42 + 0.42 g a.i. ha1) did not provide commercially effective control of jio.  Control of both weeds was reduced when seeds were sown later than 0 DAT indicating that roguing out escaped weeds that might produce seed is important.  Further research on controlling these weeds in nursery and landscape situations is needed to help reduce their spread and establishment.  rstamps@ufl.edu




STEWARDSHIP OF LAND MANAGEMENT PRODUCTS AND SOLUTIONS FROM DUPONT CROP PROTECTION. D. R. Forney*1, J. S. Claus2, R. R. Magee3, R. G. Turner4; 1DuPont Crop Protection, Newark, DE, 2DuPont Crop Protection, Wilmington, DE, 3DuPont Crop Protection, League City, TX, 4DuPont Crop Protection, Memphis, TN (234)

ABSTRACT

Stewardship of Land Management Products and Solutions from DuPont Crop Protection

 

Raymond Forney*, Jon Claus, Bob Magee, Ronnie Turner, Jack Cain

DuPont Crop Protection, Wilmington, DE
raymond.forney@usa.dupont.com

 

Environmental stewardship is one of the four core values of DuPont, along with safety and health, highest ethical behavior, and respect for people. Within DuPont Crop Protection, stewardship is defined as “An integrated business process for identifying, managing, and reducing the safety, health, and environmental risks throughout all stages of a product’s life in the best interests of our customers, employees, shareholders, society and the environment.” The stewardship principles for DuPont Crop Protection around quality, safety, health and environment, safe use, change management, and a global life-cycle commitment are considered key to sustainability. They are  applied across all business activities globally, from project inception throughout the complete life cycles of products, including sourcing of raw ingredients, intermediates, and services, through the environmental fate of associated waste and packaging. DuPont’s Land Management herbicide portfolio includes products for bare ground, forestry, invasive weeds, brush, and selective markets, and is expanding with new products based on aminocyclopyrachlor. Land Management stewardship program elements include technology development and registration, education and information, customer training, program recommendations, and sales and service programs. Key stakeholders include custom applicators, crop protection chemical distributors/ retailers, land owners and managers, and university and consultant professionals. Product information is provided in various media and includes labels, MSDS, product information bulletins, and relevant technical information on special topics like invasive species, and application technology. Stewardship training modules will be offered to customers and other stakeholders ranging across numerous topics such as the importance of timely communications, pesticide safety, and ecosystem services. Stewardship and sustainability in DuPont are critical to our vision: “To be the world's most dynamic science company, creating sustainable solutions essential to a better, safer, healthier life for people everywhere.”

 




CHOPPER GEN2 APPLIED TO BAREGROUND FOR PINE SITE PREPARATION. J. L. Yeiser*1, A. W. Ezell2; 1Stephen F Austin State University, Nacogdoches, TX, 2Mississippi State University, Starkville, MS (235)

ABSTRACT

The objective of this study was to apply Chopper GEN2+Accord Concentrate+MSO to woody sprouts commonly present on loblolly pine sites at site preparation.  2007 sites were selected for early and late harvesting dates.  Sprouts were selected for different stages of development.  Two sites were tested during 2007 in each of Mississippi and Louisiana and one site was tested in each state in 2008.  GEN2+Accord Concentrate+MSO application rates in 2007 were 32oz+2qt+1% and in 2008 were 40oz+2qt+1% in a total carrier volume of 15 GPA.  Timing of application varied so as to treat unwanted woody competitors when they were 0-in (bare ground), 6-12-in, 12-24-in, and 36-in.  An untreated check was also tested at each site in each year.

Herbicides were applied with a backpack aerial simulator supporting a KLC9 nozzle.  Treatment plots were 30-ft x 100-ft.  Measurement plots were centered internally within treatment plots and were 10-ft x 80-ft.  Sum of linear sprout heights was assessed by species and used to assess weed control.  Evaluations were performed for 2007 sites one, two and three and for 2008 sites, one and two growing seasons after treatment.

All herbicide treatments reduced the sum of heights for woody competitor below the untreated check for all evaluations.  After 2 growing seasons, sprouts treated 6-in in height exhibited sum of heights comparable to initial levels.  Sum of heights for sprouts that were >12-24in tall when treated remained reduced well below initial levels for all evaluation dates.




INVASIVE SPECIES DISTRIBUTION AMONG LARGE URBAN PARK FORESTS IN THE NORTHEASTERN UNITED STATES. R. E. Loeb*; The Pennsylvania State University, DuBois, PA (236)

ABSTRACT




NEW DEVELOPMENTS IN WOODY BRUSH CONTROL WITH AMINOPYRALID TANK MIXES. V. F. Peterson*1, W. N. Kline2, P. L. Burch3; 1Dow AgroSciences, Mulino, OR, 2Dow AgroSciences, Duluth, GA, 3Dow AgroSciences, Christianburg, VA (237)

ABSTRACT

Aminopyralid (Milestone® VM Herbicide) is a herbicide developed by Dow AgroSciences for managing broadleaf weeds and brush in rights-of-way, range & pasture, forestry site (state SLN labels) and other non-cropland sites. Aminopyralid has good utility in herbaceous weed and brush management programs. The weed spectrum is broadened when combined with certain other active ingredients. A new product with aminopyralid and metsulfuron (Opensight® Herbicide) has demonstrated excellent potential as a brush control tank-mix partner. Research was conducted in 2009 to evaluate efficacy of tank mixtures containing Milestone VM and Opensight on economically important woody brush species. Comparisons were made to current market standards and aminocyclopyrachlor.

Experiments were conducted in two nursery tree field trials in Virginia and Georgia; and in one natural area strip plot field trial in Georgia. Brush species evaluated in the Virginia and Georgia nursery tree trials were sweetgum (LIQST), red maple (ACRRB), red oak (QUEFC), yellow poplar (LIRTU) and loblolly pine (PIUTD).   Species evaluated in the Georgia strip plot trial were sweetgum (LIQST), red oak (QUEFC), white oak (QUEAL) and cherry (PRNSO). Opensight + Accord, Opensight + Accord + Arsenal and Milestone VM + Accord + Arsenal provided excellent control across all species in nursery tree trials and the strip plot trial. Mixtures with Milestone VM or Opensight provided 88 to 100% control at 414 DAT across all species. Aminocyclopyrachlor provided 26 to 67% control of red oak, sweetgum, red maple, yellow poplar and loblolly pine and 87 to 97% control of white oak and cherry in the Strip Plot trial only. Escort did not improve control (41 to 75%) of red oak, sweetgum, and loblolly pine when applied with aminocyclopyrachlor, but improved red maple control from 30 to 76% and yellow poplar control from 37 to 78% compared to aminocyclopyrachlor alone. Arsenal at 24 fl oz/acre applied with aminocyclopyrachlor + Escort improved control of sweetgum, red oak, white oak, and yellow poplar compared to aminocyclopyrachlor + Escort. Aminopyralid product mixtures provided better control over a broader spectrum of brush species than aminocyclopyrachlor products.

 




THE EFFECT OF HERBICIDES AND TIMING ON LONGLEAF SEEDLING SURVIVAL AND HEIGHT GROWTH ON OLD-FIELD PLANTED SITES IN GEORGIA. E. D. Dickens*1, D. Moorhead2, B. McElvany3, R. Joyce4, W. Parker5; 1University of Georgia, Statesboro, GA, 2University of Georgia, Tifton, GA, 3University of Georgia, Soperton, GA, 4University of Georgia, Dublin, GA, 5University of Georgia, Millen, GA (238)

ABSTRACT

Georgia were planted to longleaf pine since 1999. Four newly planted longleaf old-field sites (two scalped and two non-scalped) were located in southeastern Georgia to perform a herbicide trial using Oust + Arsenal, Oustar, or Arsenal, and a control, with two or three application dates, replicated three times at each site. As of July 2008, one to four months after the herbicide treatments, longleaf survival was significantly reduced (by 22 to 32 percentage points) where the herbicide was applied within two months of planting. Overall second year longleaf pine seedling survival on these four sites ranged from 51 percent (Jenkins County site, planted 24 February 2008) to 96 percent (Treutlen County site, planted 24 September 2007). On the two scalped sites, the best herbicide treatments (mid-April, mid-May Oustar or Arsenal) improved seedling survival by zero to eight percentage points, whereas on the two non-scalped sites the best herbicide treatments (mid-April, mid-May Oustar or Arsenal) improved seedling survival by ten to twelve percentage points through two years. The mean percentage of longleaf seedlings out of the grass stage through two years were as follows: Jenkins County scalped site at 5 percent, the Laurens County scalped site at 39 percent, the Laurens non-scalp site at 45 percent, and the Treutlen County non-scalped site at 95 percent.<span style="" font-family: " Arial\?> 




CONTROL OF UNWANTED HARDWOODS WITH MIXTURES CONTAINING AMINOCYCLOPYRACHLOR IN PINE SITE PREPARATION AREAS. A. W. Ezell*1, J. L. Yeiser2; 1Mississippi State University, Starkville, MS, 2Stephen F Austin State University, Nacogdoches, TX (239)

ABSTRACT

Site preparation continues to be the primary use of herbicides in forestry applications. In the South, control of undesirable hardwoods on areas to be planted with pine is a focus of vegetation management work. Mixtures of aminocyclopyrachlor show promise for use as site preparation treatments. A total of 12 treatments were applied to recently cutover sites in MS and TX to test the efficacy of aminocyclopyrachlor mixed with other herbicides for controlling unwanted hardwood stems. Applications were completed in August, 2009 using a CO2 powered backpack sprayer with a pole extension and KLC-9 nozzle to simulate an aerial application. Prior to application, all hardwood stems in the application plots were recorded by species and height class. In October, 2010 living hardwoods in the plots were again tallied by species and height class. The results of treatment efficacy in controlling the various species of hardwoods on these sites will be reported. 



USE OF INDAZIFLAM FOR HERBACEOUS WEED CONTROL IN FIRST-YEAR LOBLOLLY PINE PLANTATIONS. A. W. Ezell*1, J. L. Yeiser2; 1Mississippi State University, Starkville, MS, 2Stephen F Austin State University, Nacogdoches, TX (240)

ABSTRACT

Indaziflam is a new herbicide for use in forestry and has potential for controlling herbaceous weeds in newly established plantations. Herbaceous weed control is considered essential for successful plantation establishment in the South, and new products which could potentially expand our spectrum of control are always welcome additions. Two studies were installed at site in both Mississippi and Texas to evaluate the use of indaziflam alone on in mixtures with imazapyr and/or sulfometuron in one study and with sulfometuron and/or hexazinone in the second study. Treatments were applied  in March, 2009 over the top of newly planted loblolly pine (Pinus taeda)seedlings. Plots were evaluated at 30 day intervals after pplication through the first growing season for both control of competing herbaceous species and for any phytotoxic syptoms on the crop seedlings. In addition, plots were evaluted in April and May, 2010 for any residual herbaceous weed control. Results indicate that indaziflam demonstrates no phytotoxic effects on loblolly pine seedlings. Mixtures with imazapyr, sulfometuron, and hexazinone produced much better control than treatments of indaziflam alone. The mixtures with indaziflam continued to provide residaul control of herbaceous weeds into the year following application.



INDAZIFLAM FOR RAILROAD WEED CONTROL. J. Ferrell*1, B. A. Sellers2, G. MacDonald1, J. Michel3, D. Spak4; 1University of Florida, Gainesville, FL, 2University of Florida, Ona, FL, 3Bayer CropScience PL, Orlando, FL, 4Bayer CropScience LP, Research Triangle Park, NC (241)

ABSTRACT

Indaziflam is a preemergence herbicide that is effective against a number of grass and broadleaf weed species.  Though the use rate is between 25 and 100 g/ha, indaziflam is capable of providing long-term control of sensitive weed species.  To determine the utility of this herbicide for bare ground industrial sites, several railroad beds across Florida were selected for product evaluation, two of which will be presented here.  Indaziflam at 50, 100, and 150 g/ha was compared with several standards including: diuron (4500 g/ha), sulfometuron (150 g/ha), diuron + bromacil (2700 + 2700 g/ha), and diuron + sulfometuron (4500 + 150 g/ha).  All treatments were applied in March 2009 and included glyphosate (3000 g ae/ha) to control existing vegetation.  Plots were evaluated for 200 days after treatment (DAT) to determine percent grass control.  At two locations in north Florida (Jacksonville and Baldwin) it was observed that all herbicides provided greater than 80% control of grasses for the first 100 days.  At both locations, indaziflam provided greater than 95% control during this same period.  By 150 DAT, indaziflam continued to provide greater than 85% control at both locations while diuron, sulfometuron, diuron + bromacil became more variable.  In Baldwin, diuron + sulfometuron provided 100% control of grasses at 150 DAT, but only 45% control in Jacksonville.  Similarly, grass control with diuron + bromacil was 20% in Baldwin while remaining at 77% in Jacksonville.  By 200 DAT, grass control with indaziflam was 95% or greater at the Baldwin location while all other herbicides provided less than 38% control.  In Jacksonville, indaziflam provided greater than 78% control while the other herbicides varied between 67 and 42% control.  These data indicate that indaziflam is an effective herbicide for railroad weed control.  Moreover, the consistency of control with indaziflam at across both locations is noteworthy when compared to the more variable commercial standards. 




AMINOCYCLOPYRACHLOR FOR RANGE AND PASTURE WEED CONTROL. S. K. Rick*1, J. H. Meredith2, J. S. Claus3, C. Alford4; 1DuPont Crop Protection, Waterloo, IL, 2DuPont Crop Protection, Memphis, TN, 3DuPont Crop Protection, Wilmington, DE, 4DuPont Crop Protection, Denver, CO (242)

ABSTRACT

DuPont Crop Protection recently discovered and is developing aminocyclopyrachlor for broadleaf weed control in pasture and rangeland.  Aminocyclopyrachlor belongs to a novel class of chemistry known as the pyrimidine carboxylic acids. This new generation of synthetic auxin chemistry has unique properties at both the molecular and whole plant level that translates into more potent herbicidal activity.  Aminocyclopyrachlor is characterized by low use rates, low toxicity to mammals and a favorable environmental profile.  Aminocyclopyrachlor demonstrates both foliar and residual activity on a broad spectrum of broadleaf weeds including many invasive species.
jeff.h.meredith@usa.dupont.com



RUSH SKELETONWEED MANAGEMENT IN GRASSLANDS WITH AMINOCYCLOPYRACHLOR. T. Prather*1, I. C. Burke2, J. Wallace1; 1University of Idaho, Moscow, ID, 2Washington State University, Pullman, WA (243)

ABSTRACT

Rush skeletonweed is found frequently in Idaho from the Panhandle Region in the north to Craters of the Moon in south-central Idaho on the Snake River Plains.  Bureau of Land Management estimates of infested areas was 3 million acres in the 1990's.  Integrating plant competition, biological control and control with herbicides is necessary for longer-term management of rush skeletonweed.  Identifying effective herbicides for control is a key component to a return of infested lands to productive plant communities.  An experiment was established near Cambridge, ID in sagebrush-steppe to evaluate rush skeletonweed (Chondrilla juncea L) control with aminocyclopyrachlor at the rosette stage in the spring (May 19, 2008) and late fall (November 17 2008), and at the floral bud stage in mid-summer (July 22, 2008).  The experiment was blocked by timing with four replications.  Aminocyclopyrachlor at 1, 2, or 3 oz ai/A was effective as a fall treatment to rosettes, a spring treatment to rosettes and as a treatment in summer to rush skeletonweed at the floral bud stage.  There was a trend toward reduced control at the floral bud stage with a rate response where control averaged 62% at 1 oz ai/A and 99% control at 3 oz ai/A.  The weedy grasses, bulbous bluegrass (Poa bulbosa L.) and downy brome (Bromus tectorum L.) were reduced with less cover when aminocyclopyrachlor was applied in the fall.  Two perennial grasses at the site, red threeawn (Aristida purpurea Nutt.) and intermediate wheatgrass (Thinopyrum intermedium Barkworth & Dewey) were present and no treatment effects were detected.  Two shrubs, big sagebrush (Artemisia tridentata Nutt.) and antelope bitterbrush (Purshia tridentata Pursh)  appeared uninjured.  Rehabilitation of rangelands for longer-term management of rush skeletonweed will benefit from increased understanding of herbicide effects on native plants and forage grasses.  In other studies we have found that, while injured, arrowleaf balsamroot (Balsamorhiza sagittata (Pursh)Nutt), silky lupine (Lupinus sericeus Pursh), and snowberry (Symphoricarpos albus (L.) S.F.Blake) all survived to flower in the year after treatment.  Established bluebunch wheatgrass (Psuedoroegneria spicata  (Pursh) A.Love) and Idaho fescue (Festuca idahoensis Elmer) are both tolerant to aminocyclopyrachlor at up to 4 oz ai/A.  As seedlings, Idaho fescue, bluebunch wheatgrass, and Sandberg bluegrass (Poa secunda J. Presl) were tolerant to 2 oz ai/A but mountain brome (Bromus marginatus Neesex Steud.) and basin wildrye (Leymus cinereus (Scribn. & Merr.) A. Love) showed signs of injury with respect to biomass or epinasty.  Aminocyclopyrachlor is effective for control of rush skeletonweed and several grass, forb and shrub species appear tolerant.




WEED CONTROL WITH AMINOCYCLOPYRACHLOR IN PASTURES AND RANGELAND. R. N. Rupp*1, M. Edwards2, J. Harbour2, J. H. Meredith3, S. K. Rick4; 1DuPont Crop Protection, Edmond, OK, 2DuPont Crop Protection, Wilmington, DE, 3DuPont Crop Protection, Memphis, TN, 4DuPont Crop Protection, Waterloo, IL (244)

ABSTRACT

DuPont Crop Protection is evaluating an exciting new active ingredient, aminocyclopyrachlor, for broadleaf weed and brush control in pastures and rangeland.  Aminocyclopyrachlor is characterized by low use rates, low toxicity to humans and wildlife and a favorable environmental profile.  Aminocyclopyrachlor demonstrates both foliar and residual activity on a broad spectrum of broadleaf weeds including invasive species. Data will be presented from trials across the United States from 2004 –2010 showing that aminocyclopyrachlor at 1-2 ozai/a controls key species of broadleaf weeds as well as several brush species, including mesquite and huisache. Crop response on rangeland and pasture grasses is minimal at rates up to 2 oz ai/A. 




IWM IS LEVEL I IPM; LET'S AIM HIGHER. R. F. Norris*; University of California, Davis, Davis, CA (245)

ABSTRACT

The term integrated weed management, often shortened to IWM, is frequently used in recent weed science publications.  IWM is, however, a subset of the broader concept of integrated pest management, usually called IPM.  Integrated pest management has its origins in arthropod management, and IPM has often been viewed to represent management of arthropod pests.  From the legal aspect of pest management in the United States under the Federal Insecticide Fungicide and Rodenticide Act, it is clear that all organisms that interfere with human activity are considered to be pests. This includes everything from bacteria and algae to rats and kudzu (actually arthropods, mollusks, nematodes,  pathogens, vertebrates, and weeds). Proponents of the adoption of IPM now recognize that management of a single pest, or category of pests, without acknowledging other pest organisms is only the simplest form of IPM, and is considered to be level I. This is the level of IWM, and should arguably be called weed IPM (or IPM for weeds).  In most ecosystems, pests in different categories cannot be managed in isolation. A farmer has no option;  all types of pests must be managed in as coordinated manner as possible. Integration of management across all categories of pests  is level II IPM. Most current IPM programs do not attain level II.  Regional level tactics are required for optimum management of some pests . Such regional pest management strategies are considered to be level III IPM, and such strategies extend beyond the control of a single manager.  Weeds must be managed because of their impacts on crop yields and interference with farming operations.  Weeds, because they are plants, are ecologically producers. From a trophic dynamics viewpoint, weed management therefore has the possibility of impacting all other organisms that might use weeds as food or shelter, including pest and beneficial arthropods, nematodes, pathogens, and pest and useful vertebrates. The role of plants often classified as weeds in providing ecosystem services is becoming increasingly recognized, especially in Europe. Due to the complex role of weeds in ecosystems  their management requires that weed science embrace the full level II IPM concept.




DO BEETLES EAT WEED SEEDS: THE EFFECT OF SITE AND SEASON ON THE DIET COMPOSITION OF A COMMON GROUND BEETLE (PTEROSTICHUS MELANARIUS) IN WESTERN OREGON VEGETABLE CROPS. L. A. Moulton*, E. Peachey, A. Greco; Oregon State University, Corvallis, OR (246)

ABSTRACT

Western Oregon farm fields are home to a diverse assemblage of beneficial ground beetles (Coleoptera: Carabidae). Among these, the common black ground beetle, Pterostichus melanarius Illiger, has been the subject of dietary studies focusing on pests and weed seeds, and many suggest that it and other carabids are important invertebrate pest and post-dispersal seed predators in agricultural landscapes. Molecular analyses have focused on identifying and quantifying specific invertebrate prey within the guts of P. melanarius, and field and lab-based trials have focused on seed predation and food preference. Consumption of food items such as worms, slugs, seeds and various insects has been established, but it is unclear what the relative frequency of food items are in their diets, and how that might be influenced by site and season. We used stable isotopes and manual gut analyses to determine the relative occurrence of plant material and invertebrate material in the diet of P. melanarius, and whether diet composition was different between sites, or seasons. This methodology may help predict and/or quantify P. melanarius’ impact on weed and invertebrate pest populations in agricultural lands.

Visual examination of the gut contents of beetles sampled from three farms in western Oregon over two growing seasons revealed that the most frequent identifiable prey items were insect and spider parts, followed by earthworm remains, unidentifiable food items and plant material. Isotopic analysis of stomach contents showed a similar result, with the signatures of ingested items being close to or indistinguishable from invertebrate prey items that were tested, and more depleted in δ13C than would be expected from a diet that was heavily influenced by plant material. Over the sample season, isotopic signatures indicated that there was little change in the trophic level of feeding between the months of July, August and September. Overall, our analysis of the gut content of Pterostichus melanarius suggests a mixed diet that is heavily influenced by invertebrate prey food sources and contains little plant material.




UTILIZING THE CRITICAL PERIOD OF WEED CONTROL CONCEPT TO OPTIMIZE HERBICIDE TIMING IN LENTIL. L. Fedoruk1, S. Shirtliffe*2, E. N. Johnson3; 1BASF Canada, Saskatoon, SK, 2University of Saskatchewan, Saskatoon, SK, 3Agriculture and Agri-Food Canada, Scott, SK (247)

ABSTRACT

Weed control in conventional lentil is difficult because lentil is a poor competitor with weeds and there are few post emergent broadleaf herbicides. Imadazilinone-tolerant lentils have more herbicide options, but the optimum timing for herbicide application is not known. The critical period of weed control (CPWC) is the period in a crop’s life cycle when the crop must be kept weed free in order to prevent yield losses. The objective of this research was to determine the CPWC for lentil to optimize herbicide timing. We made lentil remain weedy or weed-free from zero to 11 above-ground nodes to investigate the durations of weed interference and weed-free period, respectively. Lentil has a CPWC beginning at the five-node stage and continuing to the 10-node stage. We observed that the CPWC in lentil begins when weeds start to accumulate significant biomass and ends with crop canopy closure. Therefore, to maximize lentil yields, growers should consider using a residual herbicide that can eliminate weeds during this CPWC. In a separate experiment, we verified these findings with different timings and combinations of herbicides.  Application of Imazethapyr + imazamox or imazamox at the five- to six-node stage resulted in the maximize lentil yield and lowest weed biomass compared to earlier applications.




A REVIEW OF SMOTHER CROPPING AND ASSOCIATED MECHANISMS OF WEED SUPPRESSION. S. Wedryk*1, J. Cardina2; 1The Ohio State University, Columbus, OH, 2The Ohio State University, Wooster, OH (248)

ABSTRACT

Smother cropping is frequently mentioned in the literature as a technique for suppressing weed growth through competition from living plants.  However, smother cropping research has been conducted using different terms and with associated management inputs, confounding the ability to determine whether smother crops are effective in weed suppression.  This review presents an analysis of smother cropping and related mechanisms of weed suppression.  Studies were selected that tested the ability of living plants to suppress weeds without confounding inputs.  The degree of weed suppression in each smother cropping situation was rated and analyzed to determine the most and least effective species and mechanisms of weed suppression.  Mechanisms related to crop growth and development were most effective.  Ancillary management practices, such as fertilization and irrigation, contributed to smother crop effectiveness and may serve to support crop growth and development.  Crop interaction mechanisms were least effective, due to competitive interactions of component smother crops.  The most effective smother cropping systems used a variety of functional, temporal, and spatial niches.  Development of a successful smother cropping system depends on the competitive ability of the crop and its physiological and chemical attributes as well as crop complementarity within the cropping system and against target weed species.




SYNERGISM BETWEEN CEREAL RYE MULCH AND SOYBEAN PLANTING DENSITY. M. R. Ryan*1, S. B. Mirsky2, D. A. Mortensen1, J. R. Teasdale2, W. Curran1; 1The Pennsylvania State University, University Park, PA, 2USDA-ARS, Beltsville, MD (249)

ABSTRACT

Mulch from cover crops has been shown to suppress weed seed germination and emergence, especially of annual species with relatively small seed size. Increasing crop seeding rate also increases crop competitive ability by accelerating crop canopy closure. This cultural weed management practice may complement the use of mulch, because the delay in weed emergence from mulch may allow large-seeded crop plants to establish a competitive canopy, which could then shade out already-stressed weed seedlings. Based on this rationale, we hypothesized there would be a synergistic interaction between increasing rye mulch and soybean planting rate. We created a range of rye biomass and soybean densities and assessed their weed-suppressive ability alone and in combination. The experiment was conducted in 2008 and 2009 in Maryland and Pennsylvania using five levels of cereal rye residue, representing 0, 0.5, 1.0, 1.5, and 2.0 times the ambient level, and five soybean densities ranging from 0 to 74 seeds m−2. In the absence of soybean, weed biomass decreased with increasing rye mulch and weeds were completely suppressed at levels above 1,500 g m−2. In the absence of rye mulch, weed biomass decreased with increasing soybean density in 2 of 4 site–yrs. In the other 2 site-yrs, the combination of these tactics produced a synergistic interaction. Our results indicate that increasing soybean planting rate can compensate for lower cereal rye biomass levels when these tactics are combined.

 




EFFECT OF NITROGEN RATES AND PLANT DENSITY ON GROWTH INDICES OF CORN (ZEA MAYS L.) UNDER STALE SEED-BED PLANTING SYSTEM. M. Farhang far*1, H. Rahimian Mashhadi2, M. R. Bihamta2; 1University of Tehran, Karaj, Iran, 2University of Tehran, Tehran, Iran (250)

ABSTRACT

Effect of nitrogen rates and plant density on growth indices of corn (Zea mays L.) under stale seedbed planting system

Farhang far Mohammad.*, Hamid R. Mashhadi, Mohammad R. Bihamta

Department of Agronomy and Plant Breeding, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

A field study was conducted at the Agricultural Research Farm of Tehran University in 2010, to understand the influence of different nitrogen rates and plant densities on maize growth indices under stale seedbed planting system. The experiment was carried out in a split factorial randomized complete block design with three replications. Factors included tow levels of seed bed preparation (stale seedbed and common seedbed), four levels of nitrogen fertilizer (0, 270, 325 and 380 kg ha-1 urea 46 percent) and density of corn in three levels (70 000,80 000 and 90 000 plants ha-1). Corn LAI and biomass values were 13% and 20% more in SSB compare no-SSB treatment, respectively. The highest values of LAI and biomass was obtained in 380 kg ha-1 treatment. Corn height was the highest in 90 000 plants ha-1, and was significantly different Compare to other plant densities. Weed biomass values were in SSB treatment lower than no-SSB.Corn CGR was highest in SSB treatments under 380 kg ha-1. SSB system con be employed as a useful tool to better manage the weed thus improve corn growth.

*farhangfar63@gmail.com

 

 

 

 

 

 

 

Abouziema, H. F., M. F. El-Karmany, M. Singh, and S. D. Sharma. 2007. Effect of nitrogen rates and weed control treatments on maize yield and associated weeds in sandy soils. Weed Tech. 21:1049–1053.

Ampong-Nyarko, K. and S. K. de Datta. 1993. Effects of nitrogen application on growth, nitrogen use efficiency and rice-weed interaction. Weed Res. 33:269–276.

Anderson, E. L., E. J. Kamparth, and R. H. Moll. 1984. Nitrogen fertility effects on accumulation, remobilization, and partitioning of N and dry matter in corn genotypes differing in prolificacy. Agr. J. 76:397-404.

Anderson, R. L., D. L. Tanaka, A. Black, and E. E. Schweizer. 1998. Weed community and species response to crop rotation, tillage, and nitrogen fertility. Weed Tech. 12:531-536.

Baird, J. V., J. P. Zublena, and S. C. Hodges. 1994. Nitrogen Management and Water Quality, North Carolina Agricultural Extension Service. 439–442.

Caldwell, B. and C. L. Mohler. 2001. Stale seedbed practices for vegetable production. Hort. Sci. 36:703–705.

Dickson, R. L., M. Andrews, R. J. Field, and E. L. Dickson. 1990. Effect of water stress, nitrogen, and gibberellic acid on fluazifop and glyphosate activity on oats (Avena sativa). Weed Sci. 38:54–61.

Evans, S. P., S. Z. Knezevic, J. L. Lindquist, C. A. Shapiro, and E. E. Blankenship. 2003 b. Nitrogen application influences the critical period for weed control in corn. Weed Sci. 51:408–417.

Harbur, M. M., and M. D. K. Own. 2004. Response of three annual weeds to corn population density and nitrogen fertilization timing.Weed Sci. 52:545-553.

Johnson, W. C. and B. G. Mullinix. 1995. Weed management in peanut using stale seedbed techniques. Weed Sci. 43:293–297.

Johnson, G. A., T. R. Hovestad, and R. E. Greenwald. 1998. Integrated weed management using narrow maize row spacing, herbicides, and cultivation. Agr. J. 90:40–46.

Kenezevic, S. Z., S. F. Weise., and C. J. Swanton. 1995. Comparison of empirtical models depicting density of and relative area as predictors of yield loss in maize (Zea mays). Weed Res. 35: 207-215.

Mc Closkey, M. C., L. G. Firbank, A. R. Watkinsons, and D. J. Webb. 1998. Interactions between weeds of winter Wheat under different fertilizer, cultivation and weed management treatments. Weed Res. 38:11-24.

Mclachlan, S. M., M. Tollenaar, C. J. Swanton and S. F. Weise. 1993. Effect of corn induced shading on dry matter accumulation distribution and architecture of red root pigweed (Amaranthus retroflexus). Weed sci. 41: 569-573.

Pysek, P. and J. Leps¡. 1991. Response of a weed community to nitrogen fertilization: a multivariate analysis. J. Veg. Sci. 2:237–244.

Rasmussen, IA. 2004. The effect of sowing date, stale seedbed,row width and mechanical weed control on weeds and yields of organic winter wheat. Weed Res 44, 12–20.

Tollenaar, M., A. A. Dibo, A. Aguilera, S. F. Weise, and C. J. Swanton. 1994a. Effect of crop density on weed interference in maize. Agr. J. 86:591–595.

Vizantinopolus, s. and N.katranis. 1998. Weed nanagement of Amaranthus spp in corn. Weed tech. 12:145-150.

Zoschke, A. and M. Quadranti. 2002. Integrated weed management: Quo Vadis? Weed Biol. Manage. 2:1-10.




EVALUATION OF INTERACTION BETWEEN FERTILIZER RATES AND HERBICIDE DOSEAGE ON CORN WEED CONTROL. A. Zare*; University of Tehran, Karaj, Iran (251)

ABSTRACT

Evaluation of interaction between fertilizer rates and herbicide doseage on weeds corn

Zare Ahmad*, Hamid R. Mashhadi, and Hassan Alizadeh

Department of Agronomy and Plant Breeding, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

To evaluate the interaction between nitrogen fertilizer and Nicosulfuron herbicide on weed control of corn, a factorial experiment was conducted based on RCBD with three replications at Research Fields of Pardis of Tehran in Karaj in 1387. The factor of nitrogen (Urea 46%) with 4 levels (0, 180, 270 and 360 kg/ha) and the Nicosulfuron herbicide via 5 doses (0, 20, 40, 60 and 80 g ai/ha, i.e. 0, 0.5, 1, 1.5 and 2 kg trade rate/ha, respectively) were considered. The results showed that except Russian Knapweed (Acroptilon repense L.) weeds in high amounts of nitrogen fertilizer (360 kg / ha) illustrated a positive reaction and had more dry weight than other treatments of nitrogen fertilizer. Also, Nicosulfuron application via both rates 60 and 80 g/ha controlled weeds effectively regardless of field pollution with weeds. The more weed control in high amount of nitrogen fertilizer (360 kg / ha), the more rate of Nicosulfuron herbicide needed. The interaction of nitrogen fertilizer and Nicosulfuron herbicide on growth indexes of corn showed that the corn height, leaf area index, biomass (stem and leaf weight), relative growth rate and crop growth rate in the nitrogen fertilizer treatments were higher than in the nitrogen control treatment. Even though, leaf area index and crop growth rate in the treatment of 360 kg/ha were higher than all of treatments, but persistence of these index were lower than in the treatment of 270 kg/ha. The interaction of nitrogen fertilizer and Nicosulfuron herbicide on grain yield and yield components showed that the treatment of 270 kg/ha nitrogen fertilizer plus 80 g ai/ha Nicosulfuron herbicide was the highest yield. However, the least yield was observed in control treatment (no Nicosulfuron and nitrogen application). According to the fitted equations on data, to achieve the highest grain yield, 250 kg/ha nitrogen fertilizer and to obtain the 50 % of the grain yield, 38 g ai/ha Nicosulfuron herbicide dose were needed.

*zareh.ahmad@yahoo.com

 

 

Barker, D. C., S. Z. Knezevic, A. R. Martin, D. T. Walters, and J. L. Lindquist. 2006. Effect of nitrogen addition on the comparative productivity of corn and velvetleaf (Abutilon theophrasti). Weed Sci. 54:354–363.

Jornsgard, B., K. Rasmussen, J. Hill, and J. L. Christensen. 1996. Influence of nitrogen on competition between cereals and their natural weed populations. Weed Res. 36:461–470.

Kim, D. S., E. J. P. Marshall, J. C. Caseley, and P. Brain. 2005. Modelling interactions between herbicide dose and multiple weed species interference in crop–weed competition. Weed Res. 46: 175–184.

Kim, D. S., E. J. P. Marshall, J. C. Caseley, and. P. Brain. 2006b. Modelling interactions between herbicide and nitrogen in terms of weed response. Weed Res 46:490–501.

Kim, D. S., P. Brain, E. J. P. Marshall. and J. C. Caseley. 2002. Modelling herbicide dose and weed density effects on crop:weed competition. Weed Res. 42: 1–13.

Kim, D.S., E. J. P. Marshall, J. C. Caseley, and p. Brains. 2006a. Modelling the effects of sub-lethal doses of herbicide and nitrogen fertilizer on crop–weed competition.Weed Res. 46:492-502.

Knezevic, S. F., S. F. Weise, and C. J. Swanton. 1994. Interference of redroot pigweed (Amaranthus retroflexus) in corn (Zea mays).Weed Sci. 42:568–573.

Knezevic, S. Z., M. J. Horak. and R. L. Vanderlip. 1997. Relative time of redroot pigweed (Amaranthus retroflexus L.) emergence is critical in pigweed–sorghum (Sorghum bicolor L.) Moench] competition. Weed Sci. 45:502–508.

Lindquist, J. L., D. C. Barker, S. Z. Knezevic, A. R. Martin, and D. T. Walters. 2007. Comparative nitrogen uptake and distribution in corn and Velvetleaf (Abutilon theophrasti).Weed Sci.55.102-110.

Massinga, R. A., R. S. Currie, M. J. Horak, and J. Boyer. 2001. Interference of Palmer amaranth in corn. Weed Sci. 49:202-208.

Wagner, N. C., B. D. Maxwell., M. L. Taper., and L. J. Rew. 2007. Developing an empirical yield –prediction model based on Wheat and Wild out (Avena fatua) density, nitrogen and herbicide rates, and growing-season precipitation. Weed Sci. 55:652-664.




RESPECT THE ROTATION - THE KEY TO WEED RESISTANCE MANAGEMENT. H. J. Strek*1, M. Hess1, D. Hurst2; 1Bayer CropScience, Frankfurt, Germany, 2Bayer CropScience, Raleigh, NC (252)

ABSTRACT

Respect the Rotation - The Key to Weed Resistance Management.

H. J. Strek*1, M. Hess1, D. Hurst2; 1Bayer CropScience, Frankfurt, Germany, 2Bayer CropScience, Research Triangle Park, NC (252)

The adoption rate of crops genetically modified for glyphosate tolerance, along with the exclusive use of glyphosate for weed management in the American market was unprecedented in the history of agriculture.  This resulted in an exceptional level of selection pressure for resistance.  The control of glyphosate resistant Palmer amaranth (AMPA) has become difficult in many areas of the Mid-South and Southeast.  Glyphosate resistance in another Amaranthus species (waterhemp, AMATA) is also becoming more difficult to control and is spreading in the Midwest.  Once a robust resistant species becomes established in a field, the costs for weed management and the effort needed to manage it increase.   Management options recommended by the WSSA include starting clean, using a pre-emergence herbicide followed by one or two post-emergent herbicide applications on weeds that are not above a certain threshold size.  One of the major challenges is convincing farmers to adopt weed management practices that are different from their current program before resistance is an issue.  Respect the Rotation is an initiative to elevate the importance of herbicide mode of action rotation, to improve grower adoption of herbicide diversity through rotation of crops, traits and herbicide classes and to promote IWM by highlighting an essential action to improve weed resistance management through a simple and consistent message.




COMMON RAGWEED IN GLYPHOSATE-RESISTANT SUGARBEET. J. M. Stachler*, J. L. Luecke, J. M. Fisher; North Dakota State University and University of Minnesota, Fargo, ND (253)

ABSTRACT

Glyphosate-resistant sugarbeet was planted on approximately 93% of the sugarbeet acreage in Minnesota and Eastern North Dakota in 2010.  Glyphosate-resistant common ragweed was first confirmed in North Dakota in 2007 and Minnesota in 2008 and continues to increase.  Clopyralid is the only sugarbeet herbicide available to effectively control glyphosate-resistant common ragweed.  Small-plot research was conducted in 2010 to determine the rate, timing, and number of clopyralid applications necessary to manage glyphosate-resistant common ragweed in glyphosate-resistant sugarbeet.

Sugarbeet, Crystal 539RR, was planted on May 12, 2010.  Treatments were arranged factorially in a randomized complete block design having four replications.  Factors included timing (2.5, 7.6, and 17.8 cm common ragweed) and treatments.  Treatments included glyphosate applied alone at 0.84 kg ae/ha, clopyralid applied once at 53, 105, and 211 g ae/ha, clopyralid applied twice at 53 and 105 g/ha, clopyralid applied once at 105 g/ha followed by 211 g/ha, clopyralid applied twice at 53 g/ha followed by 105 g/ha, and clopyralid applied three times at 105 g/ha.  Glyphosate as the potassium salt in Roundup PowerMAX was applied alone and with clopyralid.  Ammonium sulfate was included with all treatments at 2.8 kg ai/ha.  Treatments were applied with a 4-nozzle bicycle sprayer through XR8002 nozzles calibrated to deliver 159 L/ha spray volume.

Sugarbeet injury and common ragweed control was evaluated 21 days after the initial application and at harvest.  Sugarbeet roots were harvested on September 13 and root yield and extractable sucrose calculated.  An interaction occurred between timing and treatment for sugarbeet injury and common ragweed control, but not for root yield and extractable sucrose.  Sugarbeet injury was greatest at the 2.5 cm timing and at the 211 g/ha rate at 21 days after application.  At harvest, sugarbeet injury was greatest (12 to 15%) with clopyralid applied three times at 105 g/ha.  Glyphosate at 0.84 kg/ha controlled only a maximum of 64% of common ragweed with control declining over time to no greater than 30% at harvest, confirming the presence of glyphosate resistance in the population.  At 21 days after application, common ragweed control was greatest with clopyralid applied to 2.5 cm tall plants (81 to 95%) compared to 71 to 83% for 7.6 cm tall plants and 50 to 67% for 17.8 cm tall plants.  Clopyralid applied twice at a total rate of 316 kg/ha maximized common ragweed control at harvest for each timing.  Clopyralid applied twice or more controlled >90% of common ragweed at the 2.5 cm timing, compared to only clopyralid applied at a total of 316 g/ha to greater than 7.5 cm common ragweed.  Sugarbeet root yield and extractable sucrose was greatest with the weed-free check averaged over timing.  Sugarbeet root yield and extractable sucrose was greatest when clopyralid was applied to 2.5 cm tall plants (20.4 m tons/ha and 1021 kg, respectively).  Clopyralid should be applied at least three times at a total rate of 211 kg/ha to maximize root yield and extractable sucrose and effectively control glyphosate-resistant common ragweed.




SYSTEMS TO MANAGE PERENNIAL WEEDS IN ORGANIC TRANSITION. W. C. Johnson III*; USDA-ARS, Tifton, GA (254)

ABSTRACT

There is increased interest in the southeastern U. S. to produce certified organic agronomic crops, including peanut.  Many conventional growers are interested in diversifying into organic production by using long-term fallow sites (non-improved pastures, old hayfields, or abandoned crop producing fields) and having these sites immediately certified as organic.  However, common bermudagrass frequently infests long-term fallow sites and is extremely difficult, if not outright impossible, to control in organic crop production systems.  Research trials in a site heavily infested with common bermudagrass were conducted from 2008 to 2010 to evaluate systems of perennial weed control during fallow organic transition.  Treatments evaluated were all possible combinations of two primary tillage implements (power spader, disk harrow), summer weed control (solarization, fallow tillage with a peanut digger, and non-treated control), and winter tillage (fallow tillage with a peanut digger and non-tilled control).  Weed control parameters were measured the following spring, ten months after trial initiation.  Common bermudagrass densities were reduced by combinations of summer solarization or summer tillage with a peanut digger, followed by winter tillage with a peanut digger.  The peanut digger displaced common bermudagrass and exposed the vegetative material to desiccation.  However, control was not sufficient enough to prevent re-infestation by survivors.  Perennial nutsedges were present, but at non-uniform densities.  Primary tillage with a power spader reduced yellow and purple nutsedge tuber densities compared to the disk harrow.  Tuber densities were also reduced by summer tillage with a peanut digger.  These results indicate that an integrated system of summer solarization or summer tillage with a peanut digger, followed by winter tillage with a peanut digger reduce densities of common bermudagrass.  However, using systems of this type for only one season are not effective and the weed will repopulate.  Further validation on sites with uniform densities of perennial nutsedges is needed before response of those weeds to weed control treatments can be determined.




WEED MANAGEMENT IN ORGANIC VINEYARDS. A. Shrestha*1, M. W. Fidelibus2, K. Kurtural1, M. L. Moretti1; 1California State University, Fresno, CA, 2University of California, Davis, Parlier, CA (255)

ABSTRACT

Weed management in organic vineyards continue to be a challenge due to the lack of economically sustainable alternatives.  Further, there are additional issues associated with air quality (dust and smoke) regulations with some of the non-herbicide alternate treatments in the San Joaquin Valley.  A two-year on-farm study was initiated in 2010 in an organic raisin grape vineyard and in an organic winegrape vineyard to compare several weed management options.  Treatments include steam, plowing, cultivating, and an organic herbicide.  A non-treated control at each site has also been included.  Preliminary results show that steam was less effective in raisin vineyards with raised berms but more effective in winegrape vineyards with no raised berms.  The organic herbicide provided a selective bundown effect on certain broad-leaved weed species.  The mechanical weed control treatments (plow and cultivator) provided the greatest amount of weed control.  However, there may be disadvantages associated with mechanical weed control because of the soil disturbance process.  The study is ongoing and more parameters will be evaluated to compare the sustainability of each treatment at each site.  




THE PARASITIC PLANT GENOME PROJECT: NEW TOOLS FOR UNDERSTANDING THE BIOLOGY OF OROBANCHE AND STRIGA. J. Westwood*; Virginia Tech, Blacksburg, VA (256)

ABSTRACT

Parasitic plants are among the most destructive weeds as they connect directly to the vascular system of host plants to withdraw resources and alter host physiology.  The Orobanchaceae family contains two especially troublesome parasitic genera, Striga and Orobanche.  Weediness in this family is related to the evolution of parasitism in general and the evolution of host specificity in particular.  Evolution of parasitism required the transition from autotrophism to heterotrophism and has resulted in plants with many modified features such as a haustorium, reduced roots and leaves, ability to detect chemical signals from host plants, and in some species the loss of photosynthesis.  The Parasitic Plant Genome Project (PPGP; http://ppgp.huck.psu.edu/) aims to discover the genome-wide changes associated with the parasitic lifestyle through a comparative EST analysis of three species, a facultative parasite (Triphysaria versicolor), a photosynthetically competent obligate parasite (Striga hermonthica), and an obligate holoparasite (Orobanche aegyptiaca).  Despite their striking morphological differences, the numbers and types of genes expressed in each of these species are similar, with the notable exception of missing light-harvesting gene expression in O. aegyptiaca.  Weediness in Striga and Orobanche species appears to be due to a shift in host preference toward agronomic crops.  A major component of host preference is the perception of host-derived strigolactones, but Orobanche and Striga appear to be similar to non-parasites in having genes involved in strigolactone signaling.  Examples such as this suggest that alterations in gene expression have been more important in the evolution of parasitism than gene gain or loss.




RACE-SPECIFIC HOST RESISTANCE TO STRIGA - NEW INSIGHTS INTO AN OLD FOE. M. Timko*; University of Virginia, Charlottesville, VA (257)

ABSTRACT

Members of the genus Striga, the “witchweeds”, are noxious and persistent pests in farmer’s fields and serious constraints to crop productivity especially in Africa, India, and Southeast Asia. Among the primary hosts for Striga are the major cereals (maize, sorghum, rice and millet) and grain legumes (cowpea) that are important food staples worldwide. The negative impact of parasitic plants on crop productivity increases globally each year and their potential for affecting domestic agriculture looms larger as the movement of seed resources expands on a global scale. At the present time there is a limited understanding of how Striga and other parasitic plants select a suitable host and overcome their innate defense responses in order to complete their life-cycle. In the grasses most reported resistance to Striga appears to be polygenic with a large genotype X environment interaction that limits selection efficiency. In contrast, studies of the heritability of resistance (R) to S. gesnerioides in cowpea (Vigna unguiculata L. Walp.) indicate that at least seven distinct races of S. gesnerioides parasitic on cowpea exist in West and Central Africa and in all cases, race-specific resistance is conferred by single dominant genes. Using a positional cloning strategy, we isolated and characterized RSG3-301, an R gene conferring race-specific resistance to S. gesnerioides race 3 (SG3). The cloning of RSG3-301 opens the door for further exploration of the mechanism of resistance in these unique plant-plant associations. Resistance in cowpea to S.gesnerioides parasitism appears to involve a gene-for-gene mechanism reminiscent of effector-triggered immunity (ETI) described in other host - pathogen interactions. A hallmark of ETI is the direct or indirect recognition of parasite-derived avirulence (Avr) factors and other effectors that interfere with plant innate immunity by host sensors leading to activation of defense responses. In the absence of the appropriate host R gene product, host cell structure or function is altered, suppressing defense responses and allow parasite ingress. Our current understanding of the molecular and genetic factors underlying parasite virulence and host selection will be discussed and the applicability of our finding to understanding other Striga-host interactions (e.g., S. hermonthica on corn/sorghum/millet) and interactions of other genera of parasitic angiosperms with their hosts will be presented.  We will also describe the potential these studies have to the development of novel strategies for parasite control and eradication and to contributing to the practical goal of alleviating the burden of parasitic weeds from the backs of farmers worldwide. mpt9g@virginia.edu




BIOTECHNOLOGICAL APPROACHES TO PARASITIC WEED CONTROL. R. Aly*; Newe Yaar Research Center, Ramat Yeshai, Israel (258)

ABSTRACT

R. Aly1*

 

1 Department of Plant Pathology and Weed Research, ARO, The Volcani Center

 Newe-Yaar Research Center, P.O.Box 1021, Ramat yeshai 30095, Israel.

 

* E. mail: radi@volcani.agri.gov.il, Tel: + 972-4-9539514; Fax: + 972-4-9836936

 

Parasitic weeds such as Phelipanche aegyptiaca (Orobanche aegyptiaca) represent one of the most destructive and intractable problems to agriculture in developed and developing countries. A wide variety of parasitic weed control (chemical, biological, cultural and resistant crops) has been tried. Unfortunately, most are partially effective and have significant limitations. In order to develop a new resistance strategy based on biotechnology, the following are needed: 1) A reservoir of parasite genomic DNA or ESTs. 2) Identification of genes whose products selectively inhibit the parasite growth or silence a target key-gene of the parasite. 3) Capability of the transgene products or signals to move from host to parasite.  

By using biotechnological approaches, we have generated transgenic tobacco plants expressing a cecropin peptide (sarcotoxin IA), under the control of the inducible HMG2 promoter. Transgenic lines enhanced host resistance to the parasitic weed Phelipanche aegyptiaca (showed higher numbers of aborted parasitization events, reduced Phelipanche biomass and increased host biomass). Sarcotoxin IA has no obvious effect on growth and development of transgenic host plants.

Parasitic weeds such as Phelipanche accumulate high amounts of mannitol during their development. Mannitol content in the parasite is regulated by Mannose 6-Phosphate Reductase (M6PR) gene, an essential process to Phelipanche for water and nutrient uptake from the host. In our study, we used the inverted repeat technique to silence the parasite target gene - M6PR. In this study it was shown that the endogenous M6PR mRNA from P. aegyptiaca tubercles or shoots grown on transgenic tomato plants harboring the M6PR silencing construct was reduced by 60-80%. The number of dead tubercles was also increased significantly on transgenic plants as compared with the control plants.

In order to optimize our resistance strategies, we have also studied movement and uptake of molecules and macromolecules from host to parasite. In this study it was demonstrated that a Green Fluorescent Protein (GFP) was transferred from the host companion cells to the parasite through phloem connections only.




CONTROL OF STRIGA USING IR-MAIZE: A SUCCESS STORY ďż˝ HOW LONG WILL IT LAST? J. Ransom*1, F. Kanampiu2, M. Burnet3, J. Gressel4; 1North Dakota State University, Fargo, ND, 2CIMMYT, Nairobi, Kenya, 3Hi-Cap Formulations, Tubingen, Germany, 4Weizmann Institute of Science, Rehovot, Israel (259)

ABSTRACT

Based on findings that Striga asiatica could be controlled with post-emergence applications of ALS-inhibiting herbicide to hybrid maize with ALS target site resistance, this group of herbicides was screened for Striga hermonthica control when applied with or on IR-resistant maize seed. Imazapyr and pyrithiobac were the most promising because of their persistence and were used for further development based on crop safety and Striga control.  These compounds coated to maize seed prior to planting at rates of 30-45 g ha-1 provide near season long control of Striga and increase maize yields 3-4 fold, depending on the environment and the level of Striga infestation.  Locally adapted corn inbreds and hybrids with ALS-target site resistance and techniques for applying imazapyr to the seed have now been developed and are commercially available to farmers in western Kenya.  Slow release formulations of these herbicides were developed that provide greater crop safety and increased yield at higher herbicide rates.  Given the propensity that weeds have to evolve resistance to ALS-inhibiting herbicide, the rate at which seed-applied imazapyr would be rendered infective as a Striga control treatment was modeled.  Results suggest that there is little likelihood that herbicide resistance will be a problem under normal and dry conditions with short season maize as Striga would have to be homozygously resistant.  However, with short season maize when there are early heavy rains that wash away much of the herbicides; where slow release formulations are used; and in long season maize resistance could become problematic in 10-12 seasons as there would be selection for the million fold more prevalent heterozygous resistance.  Vigilant hand weeding Striga plants that are not controlled could prolong the usefulness of this technology.  Stacking the IR gene with glyphosate resistance and using imazapyr treated seed and mid-season glyphosate treatment would control Striga season long and delay the evolution of resistance to both herbicides.




CURRENT APPROACHES TO CONTROL OF CUSCUTA. T. Lanini*; University of California, Davis, Davis, CA (260)

ABSTRACT

Dodder is a stem parasite which infests many broadleaf plants.  Dodder produces haustoria that extracts assimilates and water from the host plant, thus, leading to growth and yield reduction.   Dodder is a serious problem in many crops, including tomatoes alfalfa, onion, sugarbeet, safflower, melon, citrus, carrot, and asparagus.  Dodder is also infests other many broadleaf plants, including weeds. 

Dormancy of dodder seed is induced by a rapid desiccation of the testa, rendering the seed impermeable to water and gases. Fluctuations in soil moisture and temperature near the soil surface may initiate the breaking of dormancy of buried seed.  Studies have found temperatures for dodder germination and emergence are in the range of 18°C to 36°C, with an optimum around 30°C.  This temperature range corresponds to temperatures encountered during the spring and summer season.  In field trials, dodder emergence was observed to cease in early to mid May, despite temperatures in the optimum range for germination and emergence.

After germination, the dodder seedling emerges from the soil as a rootless, leafless stem which circumnutates in search of a host.  Dodder seedlings cannot support autotropic life, thus if no suitable host is found within a few days, the seedling dies.  Once a connection occurs between dodder and a host, the dodder seedling loses its soil connection and relies entirely on the host for nutrients and water, thus reducing the growth and yield of the host. 

Preventing infestations by rotating to non-host crops, delaying crop planting until fall for sugarbeet (Beta vulgaris), use of resistant varieties or large transplants, and preemergence herbicides have all been shown to be successful in certain crops.  Once Cuscuta attaches to a crop, some loss in growth and yield will occur, regardless of the method of control, and selective control becomes very difficult. Removal of the host by hand weeding is a common method of dodder control in row crops.  In alfalfa, dodder patches are often treated with a contact herbicide or burned with a propane flamer.  These treatments are done when dodder is first detected to prevent dodder seed production. Post attachment control often requires killing or severely injuring the host plant to avoid spread of Cuscuta to surrounding plants.  However, several herbicides have been shown to selectively suppress attached Cuscuta, but rarely is complete control obtained.  Repeat treatments of low rates of glypohosate have been used to selectively remove C. japonica from citrus and C. indecora from alfalfa.  Cuscuta attached to genetically modified, herbicide resistant crops, have not been successfully killed by treatment with herbicide in all cases, indicating that these crops will only be a partial solution to the problem.  Cuscuta control will require an integrated approach conducted over a period of many years. 




INTEGRATED CROPPING PRACTICES REDUCE THE RISK OF RESISTANCE DEVELOPMENT. R. E. Blackshaw*; Agriculture and Agri-Food Canada, Lethbridge, AB (261)

ABSTRACT

Fifteen years ago the weed resistance problem on the Canadian prairies was considered second only to that of Australia. Although weeds resistant to Group 1 and Group 2 herbicides are reasonably common today, the overall severity of the resistance problem is less than what was originally predicted. There are currently no glyphosate-resistant weeds in western Canada despite Roundup Ready canola being grown on 3 million hectares annually and widespread glyphosate use in no-till systems prevalent in this area. Contrast these results to what has occurred in other regions of the world in the last 15 years and the obvious question arises ‘Why the difference?’ A large part of the answer lies in the number of diverse crops grown and the ‘slow but sure’ adoption of integrated weed management practices on the Canadian prairies. Farmers in this region have more than a dozen economically viable crops to choose from and often grow five to seven crops on their farm in any given year. A three to five-year crop rotation is usually practiced where cereals, oilseeds and pulses are grown in alternating years. Diverse crop rotations allow greater herbicide choice and prevent the build-up of weed species adapted to one production system. Conservation tillage is currently practiced on 70% of the cropland in western Canada. Initial predictions of greater weed severity with no-till have been unfounded and weed populations have been found to universally decline after five years of no-till adoption. Layered on top of a sound foundation of conservation tillage and diverse crop rotations farmers on the Canadian prairies have adopted additional IWM practices such as higher crop seed rates, competitive cultivars, specific timing and placement of fertilizer, and periodic use of forages or cover crops in the last decade. Widespread adoption of genetically-engineered herbicide-resistant canola (Roundup Ready and Liberty Link) hasn’t had negative consequences but rather has had positive effects on managing Group 1 and Group 2 weed resistance and aiding in overall weed management as long as canola is only grown once every three or four years in a diverse crop rotation. Ongoing research and cooperative farmer studies are focused on developing a more inclusive systems approach to achieve sustainable weed management while simultaneously maintaining or improving economic crop production on the Canadian prairies. 




WEED CONTROL TACTICS AND WEED POPULATION DYNAMICS. N. R. Burgos*1, A. Lawton-Rauh2; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC (262)

ABSTRACT

Weed population dynamics is governed by a complex network of genetic, ecological and anthropogenic factors.  Herbicide-resistant weed population evolution is an example. The resultant metapopulation network is a manifestation of the impact of various factors, natural or man-made, on weed establishment (germination and emergence), persistence, escape from management strategies, seed production, and life history timing.  Many groups are working on weed population dynamics models in an attempt to foretell the effects of local and regional agricultural practices and impending climate change on weed population establishment and proliferation. The most influential parameters in these models include base soil temperature, base soil water potential, and tillage – all related to weed establishment. Because our agricultural practices alter these parameters, and the biology/physiology of crops and weed species differ, we need information on weed biology as it relates to population and species interactions in the evolutionary context to make more informative, effective weed management decisions.   Research and actual field conditions indicate that continuous tillage favors annual weeds while long term zero tillage favors perennial weeds. Mowing favors species with prostrate and creeping growth habits such as Digitaria spp. and Trifolium spp.  In China, long-term handweeding and de-topping of weedy rice (Oryza sativa L.) produced biotypes that are as tall, or shorter than, the cultivated rice varieties.  These biotypes are thus barely distinguishable from cultivated rice, except for early maturation and significantly higher grain shattering.  In the US, where handweeding or de-topping are not practiced, weedy rice biotypes are up to 180 cm tall while rice cultivars are around 100 cm tall. Various weedy traits play a role in weed adaptations including early germination, rapid growth, sexual and asexual reproduction behavior, high fecundity, asynchronous maturation and emergence, dormancy, seed longevity, tolerance to biotic and abiotic stress, stress avoidance, high genetic variation, high competitive ability, or allelopathy.  Weed adaptation to management tactics can vary in rate (slow to fast), depending on how many traits are affected and the genetic basis for fastest adaptive response without compromising allele frequencies for other traits that lead to continued persistence through other selective pressures which may not be as strong.  For example, the response to mowing would be fast due to strong selection pressure from the lethality of total loss of plant stature, but this rate would be tempered by the developmental regulatory pathways that can compensate without compromising competitive ability.  On the other hand, the derivation of a new weed biotype, as in the case of weedy rice arising from adaptation to rice cultivation practices, or the origin and spread of herbicide resistance in Palmer amaranth, would be slow at first due to immediate impact on fecundity.  Following an initial slow rate of adaptation, a period of rapid population expansion could occur once adaptive alleles are derived through mutation or gene flow with other populations or species with highly adapted genotypes (such as herbicide resistance).  The origin and spread of such adaptive alleles would depend upon the number of genes involved in the adaptation, the coalescent age (whether adaptive mutations are randomly segregating in ancestral populations that predate the selective stressor) and fitness impact of adaptive alleles, and whether multiple molecular pathways can circumvent the stressor and lead to adaptation in the weedy species.  Furthermore, if the metapopulation network includes intra and/or interspecific gene flow, then it is necessary to determine if the genetic basis for adaptation in the weedy species is independently derived within populations or the result of alleles spreading between populations and/or species.  Improved understanding of the genetic controls of weedy traits as they relate to phenotypic variance and response rates will hopefully yield novel nonchemical weed control tools or approaches that are profitable, without compromising the broader ecosystem.

 




THE NEEDLE IN THE HAYSTACK: KEEPING IT LOST. F. Forcella*; USDA, Morris, MN (263)

ABSTRACT

A recent advertisement on American commercial television depicts a well-dressed young man reaching into a haystack. In less than a second he removes his hand from the straw and briefly examines something held between his thumb and forefinger. With feigned surprise and a slight smirk, he quips, “Huh, found it.” Needle in a haystack, resistance in a population, one in a billion: all seem equally rare.  Why then are there so many resistant weeds nowadays, and how might we prevent even more of them? Explicit answers are in other reports associated with the “Nonchemical Tactics in Herbicide Resistance Management” symposium, and they will not be listed here. Instead, two ideas related to the symposium topic, but only marginally related to one another, will be explored here. Hopefully each will be at least entertaining if not informative for the audience. The first topic involves the human dimensions of resistance prevention and management. In other words, we know what is necessary, so why don’t we do it? The second describes a new form of physical weed control, air-propelled abrasive grit. It is not a panacea for resistance management, but merely one more little hammer among many in the toolbox. In the agricultural system that has evolved in the USA, weed scientists interact with individuals and groups positioned at many different levels. Weed scientists basically serve as coaches to these entities, who effectively are our clients. Coaches must ask who their clients are (growers, policy makers, etc.), in what manner they relate to them, whether client behavior should be changed, and if so, how? If change is desired, there are three basic elements to it: the desire to change, the ability to change, and in some cases at least, permission to change. Desire is affected by awareness and perception. Extension educators have developed highly informative materials for making growers aware of resistance issues, but not all growers perceive the issue similarly. Some behaviorists link the desire to change inversely with wealth; i.e. change could kill the goose that lays golden eggs. The ability to change agronomic behaviors has three components: psychological, financial, and environmental. Fear of change is paralyzing for some. Change may not be feasible for others if it entails even short-term reductions in net income. And growers on gumbo soils, for example, simply have fewer options for successful change than growers with soils that are more versatile. Permission to change involves consent from higher authorities. Land owners, bankers, regulators, etc. can stymie change regardless of preferences of growers. Behaviorists suggest that the outcome of coach/client relationships reflects upon both the client and the coach, not just the client imperfectly following the coach’s advice. Thus, weed scientists may have to inquire, “How have we contributed to the issue at hand?” Behaviorists also talk about “force fields,” with multiple and opposing driving and restraining forces. Have weed scientists unwittingly had a hand in both? Can the identification and measurement of those forces assist in affecting the change that is needed to keep needles lost?  Physical weed control likely will never exceed the efficacy and efficiency of chemical control. Nevertheless, some physical control methods are very effective. Many of these techniques involve soil disturbance, and therein reside the problems of organic matter losses, erodible soils, and greenhouse gas emissions. Air-propelled abrasive grit may help alleviate this problem for both in-row and between-row, selective, postemergence control without cultivation. Grit can be derived from agricultural residues (corn cobs, nut shells), organically approved fertilizers (alfalfa meal, corn gluten meal, seed meals, poultry manure), mineral fertilizers (lime, gypsum), and bioenergy residues (dried distillers grain, biochar). Nutrient- and carbon-laden grit not only affects weed control, but also supplies needed fertilizers to crops and adds stable forms of carbon to soil. Two timely applications of grit, totaling about 1000 kg ha-1, provide season-long weed control in field corn and maintain high crop yields. Abrasive grit never will replace herbicides, but in situations where non-chemical and non-soil disturbing forms of control are needed, it represents a potential solution. In so doing, it can assist with limiting new incidences of herbicide resistance and help control populations already resistant.



PREVENTING THE SPREAD OF HERBICIDE RESISTANCE. B. D. Maxwell*; Montana State University, Bozeman, MT (264)

ABSTRACT

The objective of our research was to identify general herbicide resistance management strategies that can slow the spread of resistance across regions and to adjacent fields within a region.  Glyphosate resistant Conyza canadensis growing in regions with glyphosate tolerant soybeans and corn served as a model species to consider for simulations. Resistance spread was studied within a simulated region (county scale) using a cellular automata model where each cells in the model was a field or interfiled non-crop land use. The regional model indicated that creating isolation buffers 3 to 4 fields wide around glyphosate resistant soybean fields would minimize glyphosate resistance in populations more than any changes in crop rotation to reduce selection for resistance. Management strategies would need to be implemented at the landscape scale and therefore would cross land-ownership boundaries. Thus, effective area-wide management strategies should be in the domain of state or federal regulatory agencies.




GENE FLOW FROM HERBICIDE RESISTANT CROPS: WILL IT REVIVE NON-CHEMICAL WEED MANAGEMENT TACTICS? C. Mallory-Smith*, A. G. Hulting; Oregon State University, Corvallis, OR (265)

ABSTRACT

Gene flow has long been raised as a concern with the release of herbicide-resistant crops, but not usually because gene flow will complicate weed management.  Rather, gene flow has been used by some as an argument against the introduction of transgenic crops because they believe transgenic crops will have a negative impact on the environment.  Mechanisms of gene flow important from a practical weed management perspective include not only pollen movement but also movement of seed and vegetatively reproductive propagules.  Gene flow does have the potential to produce herbicide-resistant weeds either by hybridization with a weed species or with a nonresistant compatible crop, or by producing volunteers in rotational crops.  However, we should not forget that many herbicide-resistant crops are not transgenic but have been produced through traditional plant breeding techniques so it is not the technology that is important but rather the trait.  In the short term, it is doubtful that gene flow will create a revival of nonchemical weed control tactics.  Most production agriculture will continue to rely solely or heavily on the use of herbicides for weed management.  There will be a continued effort to bring herbicides with different sites of action into herbicide-resistant cropping systems to replace the herbicides that are no longer effective in the system. This situation has developed in part because weed scientist have become as dependent on recommending herbicides as growers have become for using them for weed control.  This dependence is viewed, by scientists both within and outside the weed science discipline, to lack creativity and innovation.  It is critical that we do expand the number of weed management methods that are used across all production systems and that these tactics include nonchemical strategies. Herbicide-resistant weed populations produced either by gene flow and by selection pressure of repeated use of herbicides with the same site of action continue to increase and new herbicides will not be discovered and deployed at the same rate.  It is time for our discipline to become more accepting and supportive of scientists with new views and ideas that may reduce the tendency of our discipline to be over-reliant on chemical weed control technology.  




INTEGRATING NONCHEMICAL PRACTICES INTO SIMULATION MODELING FOR HERBICIDE RESISTANCE: A PROACTIVE STRATEGY. J. K. Norsworthy*1, M. V. Bagavathiannan1, P. Neve2, K. L. Smith3, I. Zelaya4; 1University of Arkansas, Fayetteville, AR, 2University of Warwick, Wellesbourne, England, 3University of Arkansas, Monticello, Monticello, AR, 4Syngenta, Jealot Hills, England (266)

ABSTRACT

The increasing occurrences of herbicide resistance pose great challenges to current weed management programs. As a result of sustained selection with herbicides, weeds have continued to evolve herbicide resistance; hence, there is an urgent need to understand nonchemical strategies that can be integrated with herbicide-based weed management programs to best reduce the risk of herbicide resistance evolving.   So far, attempts have been made to investigate suitable resistance management programs once resistance has already become wide-spread, and herbicide programs have been the main focus of these efforts.  Little research has been conducted on ways to prevent or slow incidences as a proactive approach. Simulation models are valuable tools to examine the relative contribution of different factors to the overall risk of resistance evolving. Herbicide resistance simulation models have been developed to investigate the evolution of herbicide resistance in Palmer amaranth and barnyardgrass. These models will be used to test the value of different nonchemical practices in slowing the rate of evolution of resistance. The presentation will be based on the knowledge obtained from these two models. In particular, the discussions will focus on ascertaining the effectiveness of different cultural practices including crop rotation, planting dates, crop density, seed predation rates, tillage, cover crops, and others in reducing the overall risk of resistance.  By quantifying the impact of each cultural practice on the reduction in risks of resistance, a hierarchy of best management practices for mitigating resistance can be established based on model outputs.



IMPACT OF COVER CROP RESIDUE AND TILLAGE ON THE CONTROL OF GLYPHOSATE-RESISTANT PALMER AMARANTH. A. S. Culpepper*1, L. M. Sosnoskie1, J. Kichler2, L. E. Steckel3; 1University of Georgia, Tifton, GA, 2University of Georgia, Oglethorpe, GA, 3University of Tennessee, Jackson, TN (267)

ABSTRACT

During 2010, many Georgia cotton growers spent in excess of $60/A for herbicides to control glyphosate-resistant Palmer amaranth.  Even with this level of herbicide input, 92% of these growers also had to hand weed 54% of the crop with an average expense of $23.70/A.  With these costs, cotton production is not sustainable and a more economically effective integrated program must be developed.  An experiment integrating rye cover crop residue and/or deep tillage into typical herbicide systems was conducted in 2009 and again in 2010.

 

The experiment was conducted under dryland conditions in Macon County, Georgia.  Sites were infested with a natural population of glyphosate-resistant Palmer amaranth (>200 plants/yd).  The experiment was a randomized complete block design with a factorial arrangement of treatments.  Four tillage/cover crop regimes included 1) strip-tillage into weeds; 2) deep turning the soil 12 inches deep; 3) strip-tillage into dead rye cover crop residue; and 4) strip-tillage into dead rye cover crop residue that was planted after deep turning.  Four herbicide options included 1) no herbicide; 2) Roundup WeatherMax (22 oz/A) applied topically to 1-, 5-, and 13-leaf cotton; 3) Staple (1.7 oz/A) + Direx (1 qt/A) + Reflex (1 pt/A) + Gramoxone Inteon (2 pt/A) PRE followed by Roundup WeatherMax plus Parrlay (1.5 pt/A) topical to 4-leaf cotton and Direx (1 qt/A) + MSMA (2.5 pt/A) directed to 13-leaf cotton; and 4) Staple + Direx + Reflex + Gramoxone Inteon PRE followed by Ignite (29 oz/A) plus Parrlay topical to 4-leaf cotton and Direx + MSMA directed to 13-leaf cotton.  Both the deep tillage and planting of the rye cover crop (1.5 bu/A) occurred in the previous fall.  Once the cover crop reached 7 feet in height, it and all emerged weeds were terminated with cotton being planted two weeks later.  Both Roundup systems and the non-treated control were planted with DP 1050 BGRF cotton while the Ignite system was planted with Phytogen’s Widestrike 375 WRF cotton cultivar. 

 

In the absence of herbicides, deep turning the soil reduced Palmer amaranth emergence 50% at 21 d after planting.  The rye cover crop was 10% more effective than deep turning at reducing Palmer amaranth emergence; a combination of deep turning plus the cover crop reduced Palmer emergence 75%.  In the rye residue system, an average control rating of only 60% was achieved because the strip-tillage implement destroyed the residue in the row and permitted weed emergence; control was over 90% in the row middle where the rye was not disturbed.  Control from the Roundup only system was similar to the no herbicide control throughout the season.

 

In the Roundup-based system using residual herbicides, control of 59% was observed at harvest when strip-tilling into weeds.  Control was improved by 17 to 19% with the addition of deep turning or rye residue.  Deep turning plus rye residue coupled with the Roundup-based residual herbicide system provided 94% control.  Lint cotton yield of only 480 lb/A was collected when strip-tilling into weeds.  For the integrated Roundup program, deep turning, rye residue, and deep turning plus rye residue increased yields 23, 43, and 64%, respectively, when compared to strip-tilling into weeds.  Although the deep turning or rye residue systems provided similar levels of Palmer amaranth control, greater yields in the rye residue system were likely noted because of greater moisture preservation. 

 

In the Ignite-based system, control of 94% was observed at harvest when strip-tilling into weeds.  Control was improved by 5% with the addition of deep turning, rye residue, or deep turning plus rye residue.  Lint cotton yield of 625 lb/A was collected from the system when strip-tilling into weeds.  Yields of 680, 710, and 770 lb/A were noted in the Ignite systems when deep turning, using rye residue, and deep turning plus rye residue, respectively.  Similar to the results from the Roundup programs, cotton yields appeared to be greater in the presence of a rye cover residue because of greater moisture preservation in this dryland experiment.

 




ENGINEERED RESISTANCE TO HPPD INHIBITORS, THE NEXT GENERATION OF WEED MANAGEMENT IN SOYBEAN. B. S. Manley*1, G. D. Vail2, B. Vernooij1, K. Terpstra3, A. Silverstone1; 1Syngenta Biotechnology, Inc., Research Triangle Park, NC, 2Syngenta, Greensboro, NC, 3Syngenta Seeds, Inc., Clinton, IL (268)

ABSTRACT

The convenience, simplicity and cost-effectiveness of glyphosate coupled with glyphosate tolerance (GT) traits helped drive wide-spread adoption of the system first in soybeans and cotton followed by corn and other crops. The overuse of glyphosate has resulted in the onset and rapid spread of glyphosate-resistant weed populations. There are currently 11 species with confirmed resistance to glyphosate in the United States. Many of these populations have multiple resistance mechanisms with resistance to multiple herbicide modes of action. Traditional soybean selective herbicides are typically not able to fully manage these populations, so soybean growers have limited options to control weeds. 

 

Corn herbicides based on mesotrione and Callisto Plant Technology® solutions are first in class and provide corn growers with: 1) unprecedented broadleaf weed control including ALS-, triazine-, PPO-, and glyphosate-resistant weeds, 2) exceptional crop safety, 3) residual control, 4) flexibility, and 5) weed resistance management. Mesotrione is the foundation of leading corn herbicides including Callisto®, Lumax®, and Halex® GT. 

 

Syngenta scientists discovered that tolerance to mesotrione in some grasses was partly due to a tolerant target enzyme. One of these enzymes was used to engineer tolerance in soybeans to HPPD-inhibiting herbicides. Field trials conducted in the USA and Argentina from 2008 to 2010 have confirmed robust tolerance to mesotrione.  Studies for regulatory approval and commercialization are ongoing. HPPD tolerance is currently being incorporated into elite NK® brand soybean germplasm. Bringing HPPD tolerant soybeans to the market will deliver a new level of weed control performance and simplicity to North American soybean growers while providing an excellent solution for glyphosate-resistant weeds.

 

 

 

 

Lumax is a Restricted Use Pesticide.

 

HPPD tolerant soybeans are not currently registered for sale or use in the U.S. Callisto, Halex GT, Lumax, and Syngenta’s mesotrione family of herbicides are not currently registered for sale or use in soybeans in the US. 




CROP TOLERANCE AND YIELD OF DOW AGROSCIENCES HERBICIDE TRAIT TECHNOLOGY IN CORN. J. M. Ellis*1, S. C. Ditmarsen2, D. M. Simpson3, D. C. Ruen4, S. M. Ferguson5, N. N. Carranza6, C. A. Gallup7, B. W. Hopkins8; 1Dow AgroSciences, Smithville, MO, 2Dow AgroSciences, Madison, WI, 3Dow AgroSciences, Indianapolis, IN, 4Dow AgroSciences, Lanesboro, MN, 5Dow AgroSciences, Omaha, NE, 6Dow AgroSciences, Bogota, Colombia, 7Dow AgroSciences, Davenport, IA, 8Dow AgroSciences, Westerville, OH (269)

ABSTRACT

Crop Tolerance and Yield of Dow AgroSciences Herbicide Trait Technology in Corn.  Jeff M. Ellis, Scott C. Ditmarsen, David M. Simpson, David C. Ruen, Samuel M. Ferguson, Nelson M. Carranza, Courtney A. Gallup, and Bradley W. Hopkins, Dow AgroSciences, Indianapolis, IN.

 

Dow AgroSciences is currently developing two new herbicide tolerant traits.  The DHT1 trait in field corn has been extensively tested in field research trials since 2006 and has exhibited excellent tolerance to 2,4-D in single and sequential applications at preemergence, V4, and/or V7 stages of growth at rates up to 4480 g ae/ha per application.  In 2010, additional research trials were conducted to evaluate crop tolerance and yield effects from similar application timing and rate strategies.  Results of these trials confirmed earlier findings and demonstrated excellent DHT1 corn plant, brace root, and brittlesnap tolerance to both 2,4-D alone and 2,4-D + glyphosate combinations.  No negative effects on crop yield were observed in DHT1 corn.

 

This robust level of crop tolerance across a wide range of growth stages will enable expanded use patterns of 2,4-D.  DHT1, when stacked with glyphosate or other herbicide tolerant traits will provide broad spectrum grass and broadleaf weed control.  Dow AgroSciences herbicide trait technology will offer excellent crop tolerance and weed management flexibility in field corn, including efficacy on many glyphosate resistant or difficult-to-control broadleaf weed species.




DHT SOYBEAN YIELD COMPONENTS RESPONSE TO POSTEMERGENCE APPLICATIONS OF 2,4-D. A. P. Robinson*1, D. M. Simpson2, W. G. Johnson1; 1Purdue University, West Lafayette, IN, 2Dow AgroSciences, Indianapolis, IN (270)

ABSTRACT

The over-reliance and continued use of glyphosate as the sole mechanism for weed control has led to the selection of glyphosate-resistant weeds. New trait technology incorporating 2,4-D tolerance in soybean will provide an alternative method to control glyphosate-resistant weeds and reduce selection pressure by tank mixing herbicides with 2,4-D, but the response of 2,4-D on DowAgroSciences Herbicide Tolerant (DHT) soybean yield components has not been evaluated. Our objective was to quantify the effects of 2,4-D timing and rates on DHT soybean yield components. Four rates (0, 1120, 2240 and 4480 g ae ha-1) were applied at V5, R2 and V5 followed by R2 soybean growth stages at Fowler, IN in 2008 and 2009 and at Wanatah, IN in 2009. Yield, seed number, seed per pod and pod number were not changed (P ≤ 0.05) when compared across rates, application timings, or rates × application timings. Seed mass was reduced at the 4480 compared to 2240 g ae ha-1, but there were no difference in seed mass when compared across application timings or rates × application timings. We conclude that DHT soybean plants can tolerate high rates of 2,4-D while not reducing yield.




WEED CONTROL IN DICAMBA-RESISTANT SOYBEANS. C. B. Brabham*1, B. Johnson1, B. G. Young2, J. M. Matthews2, P. T. Marquardt1, C. Slack3, K. W. Bradley4, A. York5, A. S. Culpepper6, A. Hager7, K. Al-Khatib8, L. E. Steckel9, M. Moechnig10, M. Loux11, M. L. Bernards12, R. J. Smeda4; 1Purdue University, West Lafayette, IN, 2Southern Illinois University, Carbondale, IL, 3University of Kentucky, Lexington, KY, 4University of Missouri, Columbia, MO, 5North Carolina State University, Raleigh, NC, 6University of Georgia, Tifton, GA, 7University of Illinois, Urbana, IL, 8Kansas State University, Manhattan, KS, 9University of Tennessee, Jackson, TN, 10South Dakota State University, Brookings, SD, 11The Ohio State University, Columbus, OH, 12University of Nebraska-Lincoln, Lincoln, NE (271)

ABSTRACT

   Field experiments were conducted in 11 states to evaluate broadleaf weed management programs in dicamba-resistant soybeans which involved the use of preemergence and postemergence dicamba. Preemergence (PRE) dicamba at 0.25 lb ae/acre provided less than 60% control of smooth pigweed, giant ragweed, velvetleaf, palmer amaranth, waterhemp, and morningglory spp., but 97% control of common lambsquarters and horseweed at 3 weeks after treatment (WAT). Preemergence flumioxazin plus chlorimuron or sulfentrazone plus cloransulam provided 66 to 100% control of these weeds. Use of dicamba postemergence (POST) improved uniformity of control of velvetleaf, smooth pigweed, morningglory, and glyphosate-susceptible waterhemp. However, combining dicamba at 0.25 lb/acre with glyphosate resulted in 30% to 65% greater control of glyphosate-resistant palmer amaranth, glyphosate-resistant common waterhemp, glyphosate-resistant horseweed, and glyphosate-resistant giant ragweed compared to sequentially applied glyphosate.




MANAGEMENT OF GLYPHOSATE-RESISTANT WATERHEMP AND COMMON RAGWEED IN DICAMBA-RESISTANT SOYBEANS. R. J. Smeda*1, S. Seifert-Higgins2; 1University of Missouri, Columbia, MO, 2Monsanto Company, St. Louis, MO (272)

ABSTRACT

Glyphosate-resistant (Gly-R) weeds are becoming more prevalent across the landscape of Midwest corn and soybean production systems.  Forthcoming technology with dicamba-resistant soybean offers an effective, new postemergence (POST) tool for broadleaf weeds.  Research trials in conventional and no-tillage dicamba-resistant soybean were established in mid-Missouri to determine the effectiveness of managing Gly-R common waterhemp (Amaranthus rudis) and common ragweed (Ambrosia artemisiifolia).  In the presence and absence of flumioxazin (0.07 kg ai/ha) at planting (conventionalas well as no-tillage) or 2 weeks before planting (no-tillage combined with 2,4-D), individual or combined applications of glyphosate (0.86 kg ae/ha) and dicamba (0.14, 0.28, or 0.56 kg ae/ha) were broadcasted on 10 to 15 cm common waterhemp and common ragweed; in the conventional tillage trial, a sequential application of glyphosate was also made on 7 to 15 cm regrowth.  For the no-tillage trial, encapsulated acetochlor (1.26 kg ai/ha) was applied with some treatments at the initial POST timing.  Flumioxazin resulted in greater than 93% control of waterhemp and ragweed 14 days after planting (DAP) in the conventional soybean.    By 31 DAP (timing of initial postemergence applications), flumioxazin resulted in >76%  and >89% control of common ragweed and common waterhemp, respectively.  In the absence of flumioxazin, common waterhemp and ragweed control with glyphosate alone at 25 days after treatment (DAT)(57 DAP) was less than 50%; inclusion of 0.14 or 0.28 kg/ha dicamba boosted control of the respective species up to 85 and 75%.  Where flumioxazin was used, POST glyphosate resulted in 70 and 61% control of common waterhemp and ragweed, respectively by 14 DAT.  However, control of both species was up to 99% when flumioxazin was followed by glyphosate + dicamba + acetochlor.  For no-tillage soybean, use of 2,4-D as a burndown (23 days before planting) resulted in >90% weed control at the time of planting.  By 14 DAP, flumioxazin + glyphosate applied at planting was ineffective for control of common waterhemp and ragweed; addition of 0.56 kg/ha dicamba improved weed control to 95%.  Three weeks after the last POST applications, common waterhemp and ragweed control was only 36 and 70% respectively, when flumioxazin was used followed by glyphosate alone.  However, addition of dicamba at 0.28 kg/ha POST improved control of the respective species to 82 and 99%.  With herbicide use and soybean competition, control of common waterhemp and ragweed was 90% or greater at the end of the season, but this was only observed in plots treated with flumioxazin and dicamba or sequential applications of dicamba.  Optimum season-long management of spring emerging (common ragweed) or continually emerging (common waterhemp) Gly-R weeds requires the concerted activity of both preemergence and postemergence herbicides; dicamba is key to improving later season activity to acceptable levels.




EFFECT OF DICAMBA RATES ON SOYBEAN YIELD COMPONENTS. A. P. Robinson*, W. G. Johnson; Purdue University, West Lafayette, IN (273)

ABSTRACT

New trait technologies incorporating dicamba tolerance in soybean will increase the use of dicamba causing a greater potential for drift and redeposition. Previous research has shown that soybean is sensitive to dicamba, but it is unclear how yield components are affected from exposure to low quantities of dicamba. Our objective was to characterize changes in yield and yield components from dicamba rates on glyphosate-tolerant soybean. Ten rates (0, 0.05675, 0.0227, 0.5675, 1.135, 2.27, 4.54, 9.08, 22.7 and 454  g ae ha-1) were applied at three timings (V2, V5 and R2 soybean) on Becks brand 342NRR soybean planted at Lafayette, IN in 2009 and 2010 and Fowler, IN in 2009. Dose-response curves estimated that a 10% reduction in seed number was caused by 0.837, 0.561 and 0.597 g ae ha-1 of dicamba at V2, V5 and R2 respectively. Pod number was lowered by 10% from an estimated 1.18, 0.805, and 0.671 g ha-1 at V2, V5 and R2 respectively. Yield reduction followed a similar pattern, 0.755, 0.446, and 0.744 g ha-1 caused an estimated 10% loss at V2, V5 and R2 respectively. These data indicate that soybean was less affected by dicamba applications at the V2 timing and that pod production and seed number were most sensitive to dicamba rates.




SAFLUFENACIL EFFICACY ON HORSEWEED (CONYZA CANADENSIS) AND EFFECTS ON THE ABSORPTION AND TRANSLOCATION OF GLYPHOSATE. T. W. Eubank*1, V. K. Nandula1, K. N. Reddy2, D. R. Shaw3; 1Mississippi State University, Stoneville, MS, 2USDA-ARS, Stoneville, MS, 3Mississippi State University, Mississippi State, MS (274)

ABSTRACT

Saflufenacil has shown potential as an alternative means for controlling glyphosate-resistant (GR) horseweed. Saflufenacil inhibits protoporphyrinogen oxidase activity with a peroxidative mode-of-action which results in rapid necrosis and wilting of leaf tissues. This may lead to the disruption of cell membranes, which in turn, may inhibit the uptake and translocation of other herbicides when applied in combination such as glyphosate. The objectives of this study were to investigate interactions between saflufenacil and glyphosate mixtures on the control of horseweed, and to determine patterns of uptake and translocation of glyphosate applied alone and in combination with saflufenacil in horseweed.

Greenhouse studies were conducted in 2009 to evaluate the addition of glyphosate (0.4 to 1.68 kg ae ha-1) to saflufenacil (0.012 to 0.050 kg ai ha-1) on the control of GR and glyphosate-susceptible (GS) horseweed. Saflufenacil at all rates controlled both GS and GR populations at least 93% and 100% at 14 and 21 DAT, respectively and control of horseweed with the combination of saflufenacil + glyphosate was additive.

Studies were conducted in 2009 to determine saflufenacil effects on absorption and translocation of glyphosate in the GR and GS populations. Overall, GS horseweed absorbed 12 and 13% more 14C-glyphosate than GR horseweed at 24 and 48 hours after treatment (HAT), respectively. The addition of saflufenacil did reduce glyphosate absorption in GR horseweed by 7 and 13% at 24 and 72 HAT, respectively compared to GS horseweed. Generally, the addition of saflufenacil reduced 14C-glyphosate translocation in horseweed at least 6% in both populations; however, due to the exceptional efficacy of saflufenacil on horseweed these reductions did not reduce control.




PINDAR[TM] GT CONTROL OF CONYZA SP. BIOTYPES IN CALIFORNIA. M. Sorribas*1, M. L. Moretti2, A. Shrestha2, R. K. Mann1, G. W. Sthur3, M. L. Fisher3; 1Dow AgroSciences, Indianapolis, IN, 2California State University, Fresno, CA, 3Dow AgroSciences, Fresno, CA (275)

ABSTRACT

ABSTRACT

 

PindarTM GT Control of Conyza Species Biotypes in California

 

Monica Sorribas1, Marcelo L. Moretti2, Anil Shrestha2, Richard K. Mann1, Garrick W. Sthur3,
Marc L. Fisher3

 

1Dow AgroSciences, Indianapolis, Indiana; 2California State University, Fresno, California;

3Dow AgroSciences, Fresno, California


Pindar GT is a premix formulation of penoxsulam (Pindar), an ALS (acetolactate synthase) inhibitor (HRAC Group B) herbicide developed by Dow AgroSciences and registered by EPA in 2009 for use in tree nut crops and oxyfluorfen (Goal Tender®), a PPO (protoporphyrinogen oxidase) inhibitor (HRAC Group E). Pindar GT is a dual mode of action herbicide product that when applied during the winter dormant and/or spring period provides excellent residual and contact control of susceptible winter annual and spring/summer weeds in tree nuts including Malva spp. (Mallow species), Erodium spp. (Filarees), Amsinckia spp. (Fiddlenecks), Calandrinia ciliata (Redmaids), Amaranthus spp. (Pigweeds), Senecio vulgaris (Common groundsel), Sonchus spp. (Sowthistles),  Oenothera spp. (Primroses) and glyphosate susceptible and resistant Conyza canadensis (Marestail/Horseweed) and Conyza bonariensis (Fleabane) among other broadleaf weeds and common key grasses present in tree nut orchards. Pindar GT was registered by EPA in August 2010 and multiple State registrations including California were approved during the summer and spring of 2010.

In light of the increasing problematic spread of Glyphosate resistant Conyza spp. in tree nuts and other tree fruit crops in Fresno and San Joaquin Valley in California, a field trial was conducted in 2008 at the Dow AgroSciences Western Research Center in Fresno, California to determine the efficacy of Pindar GT on both species at different weed stages. Greenhouse trials were conducted in 2010 to determine the efficacy of Pindar GT versus other residual commercial herbicides to control different Conyza spp. biotypes in pre-emergence and at different post-emergence weed stages at the Western Research Center in Fresno, California. Results showed that Pindar GT at 3 pt/ac (35 gai/ha Penoxsulam+ 1680 gai/ha Oxyfluorfen) delivered pre-emergence and post-emergence control at different weed stages of different Conyza spp. populations. Additional research is in progress to extend Pindar™ GT testing to other glyphosate resistant populations.

 

®Trademark of Dow AgroSciences LLC

Pindar is not registered for sale or use in all states.  Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in all states.  Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.  Always read and follow label directions.




PINDAR GT: RESULTS OF LARGE SCALE DEMONSTRATION TRIALS IN CALIFORNIA IN 2010. J. P. Mueller*1, B. Bisabri2, M. L. Fisher3, M. Sorribas4, R. K. Mann4, D. G. Shatley5, J. Yerneni3; 1Dow AgroSciences, Brentwood, CA, 2Dow AgroSciences, Orinda, CA, 3Dow AgroSciences, Fresno, CA, 4Dow AgroSciences, Indianapolis, IN, 5Dow AgroSciences, Lincoln, CA (276)

ABSTRACT

PindarTM GT: results of large scale demonstration trials in California in 2010.

J. P. Mueller1, B. Bisabri2, M. L. Fisher3, M. Sorribas4, R. K. Mann4, D. G. Shatley5 and J. Yerneni3.

Pindar GT Herbicide (oxyfluorfen plus penoxsulam) combines two herbicidal modes of action into one product and provides long lasting pre-emergence and post-emergence control of difficult broadleaf weeds and some major grass species. This includes weeds which are resistant to other herbicides. Pindar GT is now registered for use on US tree nuts. In 2010, Pindar GT was compared to grower standard programs in 21 large scale tree nut trials applied in the winter dormant period in the San Joaquin and Sacramento Valleys of California.

The relatively high rainfall amounts which occurred in 2010 provided a challenge for residual herbicide programs. Pindar GT was shown to deliver consistent weed control across a wide range of weed species, soil types and rainfall levels. In most trials, Pindar GT performed better than the standard residual herbicide program used by the growers. Pindar GT provided four to six months control of the major broadleaf weed species infesting tree nut orchards in CA, including glyphosate - tolerant populations of Conyza (fleabane, horseweed). No crop safety or tank mixing issues occurred with Pindar GT during this extensive commercial validation project.  jpmueller@dow.com

TM Trademark of Dow AgroSciences LLC

1Dow AgroSciences, Brentwood, CA 2Dow AgroSciences, Orinda, CA 3Dow AgroSciences, Fresno, CA, 4Dow AgroSciences, Indianapolis, IN. US 5Dow AgroSciences, Lincoln, CA, USA.




HERBICIDE PROGRAMS FOR THE MANAGEMENT OF PALMER AMARANTH AND WATERHEMP IN CONVENTIONAL, GLYPHOSATE-RESISTANT, AND GLUFOSINATE-RESISTANT SOYBEANS. K. K. Rosenbaum*, T. R. Legleiter, K. W. Bradley; University of Missouri, Columbia, MO (277)

ABSTRACT

Separate field experiments were conducted in 2009 and 2010 at two locations in central and southeast Missouri to evaluate the effect of preemergence (PRE) and postemergence (POST) herbicide programs on palmer amaranth (Amaranthus palmeri S. Wats.) and common waterhemp (Amaranthus rudis Sauer) control in non-transgenic, glyphosate-resistant, and glufosinate-resistant soybean (Glycine max) production systems. At both sites, Schillinger 388TC, Asgrow AG3803 glyphosate-resistant, and MBS Genetics ML3963N glufosinate-resistant soybeans were planted at approximately 370,000 seed/ha. Palmer amaranth was the predominant species at the southeastern research location while common waterhemp was the predominant species at the central research location. Treatments included PRE-only, PRE fb POST, 2-pass POST, 1-pass POST with residual, and 1-pass POST herbicide programs relevant to the respective transgenic or non-transgenic soybean system. Results from visual control evaluations ten weeks after emergence (WAE) at the central location revealed that all PRE-only and PRE fb POST applications provided greater than 92% common waterhemp control in either soybean system, while the 2-pass POST programs provided 78 to 93% common waterhemp control, and the 1-pass POST and 1-pass POST with residual programs were more variable and provided 64 to 87% common waterhemp control. At the southeast research location, all PRE-only applications provided greater than 83% palmer amaranth control across soybean systems, while PRE fb POST applications provided from 68 to 92% palmer amaranth control, and 1-pass POST, 2-pass POST, or 1-pass POST with residual programs were extremely variable. Palmer amaranth control with POST programs in non-transgenic soybeans ranged from 18 to 30% while 2-pass POST programs in glyphosate- and glufosinate-resistant soybeans provided 86 to 90% control. In glyphosate- and glufosinate-resistant soybeans, the 1-pass POST with residual program did not increase palmer amaranth control compared to the 1-pass POST program. These results suggest that palmer amaranth is a much more difficult species to control than common waterhemp, regardless of the soybean system or herbicide program. Averaged across all herbicide programs at the central and southeast research locations, glufosinate-resistant soybeans provided the highest grain yields (3171 kg/ha central, 1924 kg/ha southeast) followed by the glyphosate-resistant soybean system (2861 kg/ha central, 1878 southeast) and the conventional soybean system (2527 kg/ha central, 1398 kg/ha southeast). Collectively, the results from these experiments indicate that programs containing PRE herbicide treatments provide the best opportunity for season-long control of common waterhemp and palmer amaranth and optimum grain yields in non-transgenic, glyphosate-resistant, or glufosinate-resistant soybean systems. 



GRAIN SORGHUM RESPONSE TO PYRASULFOTOLE & BROMOXYNIL AND GROWTH REGULATORS. N. G. Lally*1, C. R. Thompson1, D. Peterson1, L. Maddux2; 1Kansas State University, Manhattan, KS, 2Kansas State University, Rossville, KS (278)

ABSTRACT

Field experiments were conducted in 2009 at Manhattan, and Rossville, KS to evaluate grain sorghum response to POST treatments of pyrasulfotole & bromoxynil at six application timings. Two rates of pyrasulfotole & bromoxynil in a 1:8 ratio at 246 and 492 g/ha with and without 2,4-D low volatile ester at 140 g /ha were applied to sorghum at 1-, 4-, 7-, 10-, and 13-leaf collar and flag leaf growth stages. All treatments included 560 g/ha atrazine and 2.8 kg/ha ammonium sulfate. All treatments injured sorghum at all application timings. Injury was greatest 7 days after treatment (DAT)at both locations and plants were almost fully recovered by 28 DAT.  Pyrasulfotole & bromoxynil at 492 g/ha applied to 7-leaf collar sorghum produced the greatest injury of22% at Manhattan, and to 4-leaf collar sorghum at Rossville at 32%. Pyrasulfotole & bromoxynil at 492 g/ha with and without 2,4-D applied to 1-leaf sorghum delayed half bloom 3 days compared to the untreated check at Manhattan and pyrasulfotole & bromoxynil at 492 g/ha applied to 4-leaf sorghum delayed half bloom 4 days at Rossville.  At Manhattan, all treatments containing pyrasulfotole & bromoxynil except the 246 g/ha rate applied to 13-leaf collar and flag leaf sorghum reduced kernels per head 22-40% compared to the untreated check. Kernels per head were not reduced in the Rossville experiment. Thousand kernel weight was 28-33% greater for all treatments applied to flag leaf sorghum,and 25% higher with 492 g/ha of pyrasulfotole & bromoxynil +140 g/ha 2,4-D when applied to 13-leaf collar sorghum at Manhattan. At Rossville, 246 g/ha pyrasulfotole & bromoxynil + 140 g/ha 2,4-D  applied to 13-leaf collar and flag leaf sorghum increased kernel weight by 12% and pyrasulfotole & bromoxynil at 492 g/ha with and without 2,4-D applied to flag leaf sorghum increased thousand kernel weight by 12%. Pyrasulfotole & bromoxynil at 246 and 492 g/ha applied to 7-leaf collar sorghum reduced grain yield 21 and 22% at Rossville. In the Manhattan experiment, yield reductions were observed with pyrasulfotole & bromoxynil at 246 and 492 g/ha + 2,4-D at 140 g/ha applied to 7- and 13-leaf collar and flag leaf sorghum; pyrasulfotole & bromoxynil at 492 g /ha applied to 4-, 7-, and 13-leaf collars; and pyrasulfotole & bromoxynil at 246 g/ha applied to 13-leaf collar sorghum.  This data suggests a field use rate of 246 g/ha pyrasulfotole & bromoxynil applied to 1-, 4-, 7-, and 10-leaf collar sorghum could be a beneficial weed control option for grain sorghum producers.



EVALUATION OF CATTLE GRAZING PATTERNS IN RESPONSE TO HERBICIDE APPLICATIONS AND SUBSEQUENT WEED REMOVAL IN TALL FESCUE PASTURES. K. W. Bradley*, B. C. Sather, T. R. Legleiter; University of Missouri, Columbia, MO (279)

ABSTRACT

Grazing experiments were conducted during 2009 and 2010 to investigate the effect of herbicide application and subsequent weed removal on cattle grazing distribution in mixed tall fescue [Lolium arundinacea (Schreb.) S.J. Darbyshire] and legume pastures.  At each location, herbicide applications were made to one-half of the grazed acreage to remove all weeds and brush present. Weeds and legumes were left uncontrolled across the remaining half of the grazed acreage at each location for comparison. Global positioning system (GPS) tracking collars were fitted to three beef cows at each site and GPS locations of each collar were recorded at 30-minute intervals for a three- to four-month time period after herbicide application.  Weed, grass forage, and legume density in the treated and untreated areas was determined at monthly intervals after application at each site. Total forage yields (weeds plus grass forage) were also collected and separated in treated and untreated forage at monthly intervals after treatment. At each location, broadleaf weeds were substantially reduced and legumes were almost completely eliminated in herbicide-treated compared to untreated portions of the pastures.   By the end of the season, the forage grass and legume component of the total forage yields was higher and weed component lower in treated compared to untreated portions of the pastures in 2 out of 3 locations. Across all locations, by 3 months after treatment the distribution of cattle grazing herbicide-treated compared to untreated portions of the pastures increased by 8 to 19%. Overall, results from these experiments indicate that herbicide treatment and subsequent weed removal can increase forage grass yields and cattle grazing distribution in pastures with a variety of weed infestation levels.




SAFENING OF METSULFURON WITH 2,4-D IN BAHIAGRASS. B. A. Sellers*1, J. Ferrell2, G. MacDonald2; 1University of Florida, Ona, FL, 2University of Florida, Gainesville, FL (280)

ABSTRACT

Metsulfuron is a highly effective herbicide that has been labeled for use in bermudagrass pastures for many years. Previous research has found that metsulfuron applied at 21 g/ha provided more consistent and effective long-term control of blackberry species when compared to triclopyr.  However, bahiagrass phytotoxicity following metsulfuron application is usually moderate to severe; the level of phytotoxicity appears to be related to the bahiagrass cultivar, the environment, and possible tank-mix partners (antagonism).  Preliminary research revealed that the addition of 2,4-D amine to metsulfuron decreased the amount of phytotoxicity in bahiagrass.  Therefore, safening metsulfuron by the addition of 2,4-D may be a viable option for blackberry control in bahiagrass pastures.  Field experiments were initiated in 2009 near Ona, FL to evaluate the effect of metsulfuron at 12, 17, and 21 g/ha with or without 0.53 kg/ha 2,4-D amine on bahiagrass biomass production.  Herbicide treatments were applied in late April and early November to a pure stand of ‘Pensacola’ bahiagrass using an ATV-mounted sprayer calibrated to deliver 280 L/ha.  The experiment was setup as a 6 x 2 (herbicide treatment x application timing) factorial arrangment of treatments in a randomized complete block design with three replications.  Bahiagrass biomass was harvested by clipping a 0.5 x 2.5 m2 area of each plot at 4 week intervals following the spring application and following 30 cm regrowth the following spring after the winter application.  The cumulative yield data of two harvests from the spring application and the yield data from the single harvest following the winter application were used to compare treatments.  Data were subjected to ANOVA after being converted to percent of the untreated control and means were separated using Fisher’s Protected LSD when appropriate.  Overall, the spring application of metsulfuron resulted in approximately 40% less biomass than when applied in the fall.  When averaged over both application timings, the addition of 2,4-D resulted in at least 32% greater biomass than metsulfuron alone.  Although the addition of 2,4-D to metsulfuron resulted in higher bahiagrass yield as compared to metsulfuron alone, bahiagrass yield was 14 to 29% less than the untreated control.  In normal situations, a rancher would not find this level of injury to be acceptable.  However, dense blackberry infestations often limit the amount of grazing in infested pastures, making the bahiagrass that is present virtually unusable.  Therefore, ranchers would most likely accept a reduction in yield when blackberry is the predominant weed present in a particular pasture. 

 




THE EFFECT OF WEED MANAGEMENT FOLLOWING GLYPHOSATE-RESISTANT ALFALFA STAND ESTABLISHMENT ON FORAGE PRODUCTIVITY AND STAND LONGEVITY. W. J. Everman*1, J. J. Kells1, R. H. Leep1, D. Min2, A. J. Chomas1, T. Dietz1; 1Michigan State University, East Lansing, MI, 2Michigan State University, Chatham, MI (281)

ABSTRACT

Glyphosate-resistant (GR) alfalfa offers growers new options for weed control in alfalfa. One potential benefit of using GR alfalfa, is increased longevity of an alfalfa stand under frequent harvests. It is hypothesized that GR alfalfa will have a greater longevity due to removal of weed interference with minimal crop injury. To study GR alfalfa yield, weed invasion, alfalfa stand persistence and relative forage quality (RFQ), a field trial with three weed control methods (no herbicide, glyphosate, and hexazinone) under two harvest frequencies (high and moderate) was established in August 2003 at the Michigan State University Agronomy Farm in East Lansing, Michigan, USA. Alfalfa yield was not affected by herbicide treatments in most years. There were no differences in weed biomass between alfalfa treated with glyphosate and hexazinone, except in 2007. Alfalfa stand density decreased approximately 90% (from 236 to 27 plant m-2 ) while GR alfalfa yield decreased approximately 30% (from 11.04 to 7.87 Mg ha-1). Stand density of GR alfalfa showed natural thinning over the seven year period regardless of harvest intensity or herbicide treatment. In more than half of the production years (four out of six years), relative forage quality of GR alfalfa was significantly higher under a high intensity harvesting system than a moderate intensity harvesting system. RFQ was not affected by weed removal with herbicides in most years. Weed removal and harvest intensity in established GR alfalfa  ha dno effect on stand persistence.




WARM SEASON PERENNIAL WEED CONTROL IN COOL SEASON GRASS HAY. W. Witt*; University of Kentucky, Lexington, KY (282)

ABSTRACT

Tall fescue, orchardgrass and timothy are cool-season grasses frequently used for beef and horse hay in Kentucky.  Tall ironweed, smooth groundcherry, and Carolina horsenettle occur frequently in these hayfields and reduce hay yield or reduce the quality of the hay.  Tall fescue and orchardgrass may be used as pasture and a hay crop removed either before or after grazing by beef animals. Sericia lespedeza, blackberries and multiflora rose may occur in these fields in addition to the weeds mentioned previously. Mowing during the hay harvest does not provide control of these species. Experiments were conducted in 2006 through 2010 to compare the relative effectiveness of herbicides for the control of these weeds.  All treatments in all experiments contained three or four replications, individual plot sizes were 3m by 10m and treatments applied at 140 L/ha or 190 L/ha.  Control was based on a visual estimate using a 0-100 scale. Treatments providing greater than 80% control of tall ironweed and smooth groundcherry contained triclopyr, aminopyralid, or aminocyclopyrachlor.  Greater than 85% of Carolina horsenettle was provided by treatments containing aminopyralid, dicamba, or metsulfuron. Treatments containing aminopyralid or metsulfuron provided greater than 80% control of Sericia lespedeza.  Forage grasses injury was not noted 30 days after treatment for any treatments.




SOLVINIX LC, THE FIRST PLANT VIRUS-BASED BIOHERBICIDE. R. Charudattan*, E. Hiebert; BioProdex, Inc., Gainesville, FL (283)

ABSTRACT




UTILITY OF AMINOPYRALID + METSULFURON FOR WEED CONTROL, SEEDHEAD AND GRASS HEIGHT SUPPRESSION IN BAHIA AND FESCUE ROADSIDES. V. F. Peterson*1, W. N. Kline2, B. B. Sleugh3, P. L. Burch4, J. Ferrell5, W. Witt6, R. J. Smeda7, S. F. Enloe8, J. L. Belcher8, F. H. Yelverton9, L. S. Warren9; 1Dow AgroSciences, Mulino, OR, 2Dow AgroSciences, Duluth, GA, 3Dow AgroSciences, Des Moines, IA, 4Dow AgroSciences, Christianburg, VA, 5University of Florida, Gainesville, FL, 6University of Kentucky, Lexington, KY, 7University of Missouri, Columbia, MO, 8Auburn University, Auburn, AL, 9North Carolina State University, Raleigh, NC (284)

ABSTRACT

Roadside managers have dual objectives to control weeds and reduce tall vegetation that affect visibility, aesthetics, and safety on roadways.   These objectives are often achieved by a combination of mowing and herbicide applications.  Mowing has become more costly with recent fuel prices and increases exposure of crews on roadsides to traffic hazards. In addition to weed control, grass height management is required because overgrown vegetation limits motorist visibility and increases hazards.  Herbicide applications containing sulfometuron-methyl, imazapic, chlorsulfron, and metsulfuron-methyl have been used as plant growth regulators (PGR’s) to suppress grass growth and seed head development on many cool- and warm-season grasses found on roadside rights-of-way.  

 

Aminopyralid + metsulfuron (Opensight®) is a new herbicide product from Dow AgroSciences for control of weeds and certain woody plants, including invasive and noxious weeds, on non-cropland areas including roadsides, electric utility and communication transmission lines, pipelines, railroads, non-irrigation ditch banks, natural areas, and grazed areas in and around these sites. Trials were established in 2010 in Alabama, Florida, Missouri, Mississippi and North Carolina to compare performance of Opensight to commercial standards for weed control, grass height and grass seed head suppression.

 

Opensight and mixtures with Opensight provided better weed control efficacy when compared to imazapic on weeds such as goldenrod (Solidago Canadensis), narrow-leaf plantain (Plantago lanceolata), common catsear (Hypochoeris radicata), cudweed (Gnaphalium sp.), poison hemlock (Conium maculatum), curly dock (Rumex crispus), hop clover (Trifolium aureum) and others.

 

In addition to weed control, Opensight provided excellent foliage height and seedhead suppression on both fescue (Schedonorus phoenix) and bahiagrass (Paspalum notatum). Across all trials, growth suppression was generally equivalent between Opensight and imazapic up to about 70 DAT.

 

Based upon these field trials, foliage injury to tall fescue from Opensight® or Plateau was minimal and should not be a concern. Foliage injury to bahiagrass from Opensight® or Plateau is significant enough to create a visual impact on roadside turf and can last for approximately 2 months. Observations from these trials, suggest that bahiagrass injury is transient, recovering after approximately 60 DAT.

 

In one trial with common bermudagrass (Cynodon dactylon), imazapic significantly injured (clorosis) and thinned the bermudagrass stand. This allowed tall growing weeds to flourish and negate the effect of this treatment to reduce mowing frequency.

 

For roadside turf management, Opensight provides weed control, grass height and seed head suppression without the need for adding imazapic. Use of Opensight will result in cost savings while delivering broad spectrum weed control and grass growth suppression.

 

®Trademark of Dow AgroSciences LLC

When treating areas in and around roadside or utility rights-of-way that are or will be grazed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details. State restrictions on the sale and use of Opensight apply. Consult the label before purchase or use for full details. Always read and follow label directions.




SUPPRESSION OF MEDUSAHEAD ESTABLISHMENT WITH PREEMERGENCE AMINOPYRALID AND AMINOCYCLOPYRACHLOR TREATMENTS. J. M. DiTomaso*, G. B. Kyser; University of California, Davis, Davis, CA (285)

ABSTRACT

Medusahead (Taeniatherum caput-medusae) is the most problematic invasive grass in California rangeland, often developing into monotypic stands.  Various control techniques, such as prescribed burning, grazing, and herbicides have been tested but are not always practicable.  Aminopyralid, normally used for selective control of certain broadleaf species such as thistles, appears to have an impact pre- or early postemergence on some grasses, including medusahead.  We tested the efficacy of aminopyralid for medusahead control, both pre- and postemergence in a greenhouse and in preemergence applications at three rangeland sites.  In a rate series study in the greenhouse, aminopyralid reduced medusahead seedling vigor 85% with 131 g a.e./ha applied preemergence or  >245 g a.e./ha early postemergence.  Preemergence treatments also suppressed seedling emergence.  Following this preliminary trial, we used only preemergence applications in the field experiments.  In foothill rangeland sites at Winters, Marysville, and Red Bluff, California, we compared a rate series of aminopyralid (53, 88, 123, and 245 g a.e./ha) with rimsulfuron and imazapic.  Plots were 3 m by 9 m in four replications at each site.  Treatments were applied in early fall.  Visual cover estimates and biomass/seedhead samples were taken in three quadrats per plot in late May.  Medusahead control was consistent across sites, at 89% with 245 g a.e./ha aminopyralid and 59% with 123 g a.e./ha.  Most other treatments produced 40% to 60% control.  Cover of other annual grasses increased in plots treated with aminopyralid at all sites, probably owing to suppression of medusahead and Asteraceae species.  Aminopyralid appears to be a good option for suppressing medusahead, particularly if a site is also infested with yellow starthistle or other problem Asteraceae.  However, at the maximum labeled broadcast rate (123 g a.e./ha), aminopyralid does not provide complete control of medusahead.  In addition, the ideal application time for medusahead control is preemergence – i.e., early fall – which is too early to provide season-long control of yellow starthistle. 



CONTINUING AMINOCYCLOPYRACHLOR RESEARCH AT COLORADO STATE UNIVERSITY. B. Lindenmayer*1, P. Westra1, S. J. Nissen1, D. L. Shaner2; 1Colorado State University, Fort Collins, CO, 2USDA, Fort Collins, CO (286)

ABSTRACT

Continued evaluation of Canada thistle (Cirsium arvense) plots treated with aminocyclopyrachlor or aminopyralid has provided additional control data and prompted further investigation.  Herbicide was applied at three rates (70, 140, and 210 g ai/ha) in three formulations of aminocyclopyrachlor and one rate of aminopyralid (126 g ai/ha) in September, 2008 to C. thistle foliage and to soil where the thistle had recently been shallowly tilled at two sites, one irrigated and one dryland site.  Biomass was collected 1, 1.5 and 2 years after treatment (YAT).  All rates of all formulations of all herbicides performed equivalently over the duration of the experiment, but the soil-applied herbicides were more effective  than foliar applied at 1 and 1.5 YAT and were equally as effective as the foliar-applied herbicides at 2 YAT.  Greater biomass was observed at the irrigated site, but overall control trends were similar at the dryland site.  A site-of-uptake study was done to determine how the herbicides were being taken up by the plants in the soil.  C. thistle root segments were planted in soil where a treated layer of soil was located above (A) or below (B) the root segments and plant growth was evaluated 28 days after treatment.  Aminocyclopyrachlor, aminopyralid, and clopyralid were all applied at 70 g ai/ha.  Shoot production and total shoot biomass for all A treatments were not significantly different between the herbicides or the untreated check. However, shoot production and biomass were significantly lower for aminocyclopyrachlor and aminopyralid when the herbicides were located below the root segments (B treatement).  Interestingly, the total root biomass was not significantly affected in either A or B treatments.  These results suggest that aminocyclopyrachlor and aminopyralid are absorbed by the root system and translocated to the shoots where growth is inhibited, but there is limited uptake by emerging shoots.  Therefore, root uptake and soil residual activity may be very important factors in perennial weed control with these herbicides.     




ALTERNATIVES FOR MSMA ALONG ROADSIDES. R. S. Wright*, J. D. Byrd; Mississippi State University, Mississippi State, MS (287)

ABSTRACT

An alternative herbicide or mixture of herbicides were evaluated against MSMA along roadsides in Mississippi for control of dallisgrass (Paspalum dilatatum), vaseygrass (Paspalum urvillei), and sericea lespedeza (Lespedeza cuneata).  All treatments were made with a CO2 pressurized backpack sprayer that delivered 236 L/ha.  Visual evaluations were made on a scale from 0 to 90% (0=no visual control; 90%= complete control visually). 

The experiment to evaluate dallisgrass control was initiated May 6, 2008.  Treatments were 80 + 158, 105 + 210, or 140 + 282 g ae/ha imazapic + glyphosate; 420, 502, or 840 g ae/ha glyphosate; 105, 140, or 175 g ae/ha imazapic; 3696 g ai/ha MSMA, and an untreated control.  All herbicide treatments were applied with a 90/10 nonionic surfactant at a rate 0.25% v/v.  Dallisgrass control was higher treated with glyphosate compared to imazapic 31 or 65 days after treatment (DAT).  Bermudagrass injury was above the 30% acceptable level with all treatments, except MSMA 31 DAT.  Dallisgrass was controlled 90% with 840 g/ha glyphosate and control with 420 or 502 g/ha ranged from 80 or 88% control, respectively, 31 DAT.  Control with 105 or 140 g/ha imazapic was 65% or 68% with 175 g/ha imazapic 31 DAT.  MSMA provided the lowest level of dallisgrass control (45% or less) 31 or 65 DAT.

The experiment conducted to evaluate control of vaseygrass or sericea lespedeza was initiated August 4, 2010.  The treatments consisted of 20 + 5, 40 + 10, or 60 + 15 g ai/ha nicosulfuron + metsulfuron methyl; 20 + 5 g ai/ha nicosulfuron + metsulfuron methyl combined with 53 + 94 g ae/ha imazapic + glyphosate, 40 + 10 g ai/ha nicosulfuron + metsulfuron methyl combined with 80 + 158 g ae/ha imazapic + glyphosate,  or 60 + 15 g ai/ha nicosulfuron + metsulfuron methyl combined with 105 + 210 g ae/ha imazapic + glyphosate; 3696 g ai/ha MSMA, and an untreated control.  All treatments were applied  a 90/10 nonionic surfactant at a rate of 0.25% v/v.  MSMA provided the highest level of vaseygrass (77%) or sericia lespedeza (67%) control 36 DAT.  Vaseygrass control was higher with imazapic + glyphosate treatments or MSMA compared to nicosulfuron + metsulfuron treatments 93 DAT.   Sericia lespedeza control was higher with 40 + 10 or 60 + 15 g/ha nicosulfuron + metsulfuron methyl (77%) or MSMA (87%) compared to imazapic + glyphosate treatments (38 to 53%) 93 DAT.   




A FRAMEWORK FOR DEFINING HERBICIDE-RESISTANT WEED BIOTYPES. W. Vencill*1, R. L. Nichols2, D. G. Shilling1; 1University of Georgia, Athens, GA, 2Cotton Incorporated, Cary, NC (288)

ABSTRACT

Herbicide resistance is an attribute of weed biology at the population, individual plant, and molecular levels. With regard to weed resistance, the term biotype is frequently used to describe (a population of) weeds from a locality that has been bio-assayed to  ascertain the level (dose or rate)of herbicide required to kill the plants  with reference to  known  susceptible plants (of the same species?).  Such a characterized collection may be reported, and thereby designated as a resistant biotype, in the Herbicide Resistance Action Committee (HRAC) database, www.weedscience.org, the reference compilation of resistant weeds.  Often the genetic mechanism conferring the resistance is unknown at the time of the report, and other collections with similar  dose-response relationships to the herbicide may or may not have the same resistance mechanism(s).  A similarly characterized collection from a neighboring geography may also be counted as a biotype. 

 

From a molecular perspective each different genetic mechanism conferring resistance against an herbicide mechanism of action is unique.  Other plants  of  the  same  species sharing  the same resistance mechanism  share the resistance  biotype.  We propose that the term ‘weed resistant biotype’ specify a unique genotype that encodes a specific resistance mechanism  expressed in phenotypes  displaying the herbicide resistance.  From this perspective the basic reporting unit in the HRAC data base should be described as a reportable population or case, and may or may not represent a unique biotype, pending characterization of the resistance mechanism they express.  We further propose that the increasing prevalence and importance of weed resistance presents the opportunity for the Weed Science Society of America to coordinate the terminology and reporting of herbicide resistance and harmonize it with that used by the other crop management disciplines. The presentation will illustrate the utility of the proposed definition by using data the HRAC database.



WATERHEMP EVOLVES RESISTANCE TO A FIFTH CLASS OF HERBICIDES, HPPD INHIBITORS. P. J. Tranel*, N. E. Hausman, S. Singh, C. Riggins, S. Rousonelos, L. Gonzini, D. Maxwell, D. E. Riechers, A. Hager; University of Illinois, Urbana, IL (289)

ABSTRACT

A population of waterhemp in a seed corn production field in central Illinois was not adequately controlled after postemergence applications of herbicides that inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD).  Progeny from the field population survived each of three different HPPD-inhibiting herbicides, applied as foliar treatments either alone or in combination with atrazine under greenhouse conditions.  Dose-response experiments indicated that the level of resistance to the HPPD inhibitor mesotrione is at least 10-fold, relative to sensitive biotypes.  Under field conditions, control of this population 14 days after postemergence application of commercial rates of mesotrione, tembotrione or topramezone was 10 percent or less, thus confirming the greenhouse results.  Additional research has revealed this population also demonstrates resistance to atrazine and simazine, and also to herbicides that inhibit acetolactate synthase. hager@illinois.edu



PALMER AMARANTH BIOTYPES RESPONSE TO HPPD INHIBITING HERBICIDES. C. R. Thompson*, N. G. Lally, D. Peterson; Kansas State University, Manhattan, KS (290)

ABSTRACT

 Palmer amaranth infests crop fields across the state of Kansas and remains one of the more difficult weed problems in Kansas crop production.  During the summer of 2009, Palmer amaranth was not controlled in a Bayer field sorghum demonstration in Stafford County with pyrasulfotole&bromoxynil 1:8 ratio applied at 245 g/ha.  During September, Palmer amaranth seed collections were made from the pyrasulfotole &bromoxynil treated area, R1, and from the remainder of the field, R2.  A known susceptible (S) source of Palmer amaranth was produced near Manhattan, KS.  Greenhouse experiments were conducted to evaluate Palmer amaranth response to pyrasulfotole&bromoxynil at several rates, field use rates of atrazine, isoxaflutole, isoxaflutole&thiencarbazone methyl 2.5:1, mesotrione and tembotrione.  All herbicides were mixed with crop oil at 1% v/v and applied to 7 to 10 cm Palmer amaranth.  Early screening suggested 7 to 11 times more pyrasulfotole&bromoxynil was required to injury the R1 and R2 collections 50% compared to the susceptible standard.  Tembotrione at 129 g/ha injury R1 and R2 85 to 90% 28 DAT and when tank mixed with 1.12 kg/ha atrazine the R1 and R2 collections were controlled 100%.  Isoxaflutole at 105 g/ha controlled R1 and S 53 and 100% 28 DAT and when mixed with 1.12 kg/ha atrazine control was 46 and 100%.  Isoxaflutole@thiencarbazone methyl at 129 g/ha controlled R1 and S 70 and 100% and when mixed with 1.12 kg/ha atrazine both collections were controlled 100%.  Mesotrione at 105 g/ha controlled R1 and S 24 and 80% 28 DAT and when mixed with 1.12 kg/ha atrazine control was 70 and 100%.  Collections R1 and R2 were not controlled with field use rates of pyrasulfotole&bromoxynil, isoxaflutole, isoxaflutole&thiencarbazone methyl, mesotrione,  or atrazine.  Previous years use of mesotrione and atrazine in corn fields in the area have likely contributed to the resistance of the R1 and R2 collections. The field use rates of tembotrione tank mixed with atrazine controlled the R1 collection 100%.  Additional information will be presented in the session.




CROSS-RESISTANCE PATTERNS OF ACETOLACTATE SYNTHASE (ALS) INHIBITOR-RESISTANT GLOBE FRINGERUSH (FIMBRISTYLIS MILIACEA) BIOTYPES IN SOUTHERN BRAZIL. C. E. Schaedler*1, J. A. Noldin2, D. Agostinetto1, N. R. Burgos3, L. C. Fontana1; 1Universidade Federal de Pelotas, Pelotas, Brazil, 2Epagri, Itajai, Brazil, 3University of Arkansas, Fayetteville, AR (291)

ABSTRACT

Weeds resistant to herbicides are widespread worldwide. Fimbristylis miliacea (FIMMI) is one of the most troublesome weeds in rice fields in southern Brazil. Acetolactate synthase (ALS)-inhibiting herbicides are widely used to control weeds in rice. The continuous use of ALS-inhibiting herbicides has led to the evolution of herbicide-resistant FIMMI. The objective of this research was to characterize resistance patterns of ALS inhibitor-resistant globe fringerush biotypes using whole-plant dose-response assays. To confirm the resistance of FIMMI to ALS inhibitors, whole-plant bioassays were conducted in 2008 and 2009 at Universidade Federal de Pelotas. The experiment was a randomized complete block design, with four replicates consisting of three factors (biotype, herbicide and rate) in a 3 x 4 x 7 factorial arrangement. The ALS herbicides were bispyribac-sodium, pyrazosulfuron-ethyl, penoxsulam and imazethapyr + imazapic. A standard herbicide treatment, bentazon, was also included because all FIMMI biotypes are susceptible to bentazon. Plants at the six-leaf stage were sprayed with herbicide equivalent to 0, 1, 2, 4, 8, 16 and 32x the full herbicide doses for the resistant biotypes (FIMMI 10 and FIMMI 12) and 0, 1/32, 1/16, 1/8, 1/4, 1/2 and 1x for the susceptible biotype (FIMMI 13).  Herbicide treatments were applied using a backpack sprayer calibrated to deliver 150 L ha-1 at 200 kPa. The efficacy on F. miliacea was visually evaluated as % control at 7, 14, 21 and 28 days after treatment (DAT) and weight of dry biomass at 28 DAT. FIMMI 10-R biotype showed cross resistance to three chemical families of ALS-inhibiting herbicides (bispyribac-sodium, pyrazosulfuron-ethyl and penoxsulam). FIMMI 12-R biotype showed cross resistance to two (pyrazosulfuron-ethyl and penoxsulam) ALS herbicide families. Bentazon is still an effective alternative to control FIMMI in areas with ALS herbicide resistance. All biotypes did not show cross resistance to imidazolinones, i.e. the premix formulation of imazethapyr + imazapic.



INVESTIGATING CROSS-RESISTANCE TO GLUFOSINATE IN GLYPHOSATE-RESISTANT ITALIAN RYEGRASS POPULATIONS. W. V. Avila*, C. Mallory-Smith; Oregon State University, Corvallis, OR (292)

ABSTRACT

Italian ryegrass (Lolium multiflorum) is one of the most competitive weeds in orchards and crops in several regions of the United States. In many orchards, the control of Italian ryegrass is based on the intensive use of glyphosate. As a consequence, several populations have evolved glyphosate-resistance in Oregon. In a routine herbicide screening test, a differential pattern of sensitivity to the herbicide glufosinate was observed among the glyphosate resistant and susceptible populations. Interestingly, there is no report of the use of glufosinate in the orchards where the populations were collected. Three Italian ryegrass glyphosate-resistant populations (OR1, OR2, and OR3) were evaluated. Glyphosate-resistance in the OR1 population is due to reduced glyphosate translocation. The mechanism of glyphosate-resistance in OR2 and OR3 appears to be the same as the mechanism in OR1 because no mutations in the EPSPS gene have been found. Therefore, dose-response, ammonia accumulation and enzyme activity studies were conducted to test the sensitivity to glufosinate in three glyphosate resistant and three susceptible Italian ryegrass populations. The rates of glufosinate required to reduce the growth in 50% (GR50) from dose response experiments were 0.15, 0.18, and 0.21 for the control populations C1, C2, and C3, respectively; whereas GR50 values for the resistant populations OR1, OR2, and OR3 were 0.49, 0.42, and 0.40 g ai ha-1, respectively. The same trend was obtained in ammonia accumulation studies where the susceptible populations accumulated two and three times more ammonia than the resistant populations at 48, 72, and 96 hours after glufosinate treatment. The I50 values of the GS enzyme activity ranged from 3.29 to 3.65 µM for the resistant populations and from 3.46 to 3.63 µM for the susceptible populations; therefore, an altered target is not responsible for the resistance to the glufosinate. Based on the results and the history of these populations, we hypothesize that reduced herbicide translocation is responsible for the cross resistance to glyphosate and glufosinate.



POTENTIAL FOR EVOLUTION OF RESISTANCE TO PYROXASULFONE IN LOLIUM RIGIDUM POPULATIONS. R. Busi*, T. A. Gaines, S. B. Powles; University of Western Australia, Crawley, WA, Australia (293)

ABSTRACT

Annual ryegrass (Lolium rigidum) is a genetically diverse, cross-pollinated species that has evolved resistance to multiple herbicides.  Pyroxasulfone is a novel pre-emergence herbicide that provides excellent annual ryegrass control, including multiple-herbicide resistant populations.  The objective of this study was to examine the dynamics of resistance evolution prior to the commercialization of this new herbicide.  The frequency of major effect genes conferring resistance to high pyroxasulfone doses was investigated by screening over 65 million annual ryegrass seeds in the field with 400 g ha-1 pyroxasulfone.  Progeny of all surviving plants were evaluated for pyroxasulfone resistance and none showed any increase in pyroxasulfone resistance when compared to the parental ryegrass populations in dose response studies, indicating that no major resistance genes were present in 65 million ryegrass individuals.  In a separate experiment, recurrent selection with sub-optimal pyroxasulfone doses was conducted in both herbicide-susceptible and multiple herbicide-resistant L. rigidum populations, S and MR.  Selected progenies were assessed for pyroxasulfone resistance relative to the unselected originator parent populations using dose-response studies.  Pyroxasulfone resistance evolved in both populations S and MR with resistant/susceptible (R/S) ratios of 1.7- and 4.2-fold based on plant survival, and 1.3- and 8.0-fold based on biomass, respectively.  The dose-response profile to several other herbicides with different modes of action indicated that a resistance mechanism providing broad-spectrum herbicide detoxification and unrelated to the herbicide site of action was likely selected.  This unprecedented study shows that repeated pyroxasulfone use at sub-optimal doses can lead to rapid herbicide resistance evolution in a cross-pollinated grass species such as L. rigidum.  Effective stewardship programs for resistance prevention must be ensured to sustain pyroxasulfone herbicide efficacy.




BIOKINETICS AND MECHANISM OF SELECTIVITY OF SAFLUFENACIL (KIXORTM). C. L. Brommer*1, K. Grossmann2, R. A. Liebl3; 1BASF, Raleigh, NC, 2BASF Agricultural Research Center, Limburgerhof, Germany, 3BASF Corporation, Research Triangle Park, NC (294)

ABSTRACT

   

Saflufenacil (KixorTM) is a new protoporpyrinogen IX oxidase (PPO) inhibiting herbicide for preplant burndown and selective preemergence dicot weed control in multiple crops, including corn. The biokinetic properties and the mechanism of selectivity of saflufenacil among corn, black nightshade and common morningglory are reported. After root treatment of plants at the third leaf stage, the phytotoxic selectivity of saflufenacil between corn and the weed species has been quantified as approximately 10-fold. The plant species showed similar selectivity following POST applications; the plant response was approximately 100-fold more sensitive to saflufenacil versus root application. PPO enzyme activity in vitro was inhibited by saflufenacil with 50% inhibition in a concentration range from 0.2 nM to 2.0 nM without clear differences between corn and the weed species. Treatments of light-grown plants and dark-grown seedlings with [14C]saflufenacil revealed that the herbicide is rapidly absorbed by root and shoot tissue. The [14C]saflufenacil was distributed within the plants systemically through acropetal and basipetal movement. Systemic [14C]saflufenacil distribution can be explained by the weak acid character of saflufenacil and its metabolic stability in the Black nightshade and Ipomea species. Metabolism of [14C]saflufenacil in corn was more rapid than in the weeds versus corn. Low translocation of root-absorbed [14C]saflufenacil in the corn shoot was observed. It is concluded that rapid metabolism in corn combined with low translocation support preemergence selectivity of saflufenacil based on physical placement in soil.




FERAL RYE STAGE OF GROWTH EFFECTS ON IMIDAZOLINONE TRANSLOCATION AND EFFICACY. M. Ostlie*1, D. L. Shaner2, P. Westra1; 1Colorado State University, Fort Collins, CO, 2USDA, Fort Collins, CO (295)

ABSTRACT

Feral rye, an obligate out-crossing winter annual grass of the same species as cultivated rye, is a major crop pest in Colorado wheat. Recent studies indicate great genetic plasticity in regards to feral rye imazamox tolerance in Colorado and Oklahoma populations. Notably, feral rye had a greater survival rate when exposed to cold temperature shortly after application, than without cold temperatures. Since imazamox can be applied in the fall in imazamox tolerant winter wheat, cold temperatures can be a factor in management decisions. To study cold weather effects, experiments were established to measure imazamox behavior in warm and cold temperatures. An experiment was designed to quantify imazamox translocation to different feral rye tissues before, during, and after vernalization. A second experiment was designed to elicit the amount of time required after application until cool temperatures affect imazamox and imazapyr efficacy. Leaf wash data indicate much slower in-take of imazamox in cold temperatures and reduced translocation to the growing points. It was observed that somewhere between 4-5 days of warm temperatures were required for maximum imazamox activity. Increased tolerance of feral rye to imazamox under cold temperatures primarily may be due to decreased translocation of herbicide along with slow metabolism of the herbicide to non-toxic forms, allowing plant recovery.




ABSORPTION, TRANSLOCATION, AND METABOLISM OF QUIZALOFOP AND RIMSULFURON IN HERBICIDE-RESISTANT GRAIN SORGHUM. J. Abit*1, K. Al-Khatib1, M. Tuinstra2; 1Kansas State University, Manhattan, KS, 2Purdue University, West Lafayette, IN (296)

ABSTRACT

Studies were conducted to determine if herbicide absorption, translocation, and metabolism are mechanisms that could explain the resistance of ACCase- and ALS-resistant grain sorghum to quizalofop and rimsulfuron, respectively. ACCase- and ALS-resistant and -susceptible genetic lines were grown under controlled conditions and treated at the 4-leaf stage with 14C-labeled quizalofop and rimsulfuron. In the ACCase experiment, at 3 d after treatment (DAT), absorption was 90% in both genotypes; at 7 DAT, however, absorption remained near steady in the susceptible but increased to 5% in the resistant genotype. Translocation of 14C-quizalofop in sorghum was similar with less than 10% of the absorbed herbicide translocated out of the treated leaf by 7 DAT. In the ACCase metabolism study, resistant grain sorghum transformed 88% of inactive quizalofop-ethyl to active quizalofop while 91% of the inactive was converted to active form by the susceptible plants 3 DAT. By 7 DAT, all inactive quizalofop-ethyl was converted to active quizalofop. For the ALS studies, results do not support the involvement of differential absorption and translocation of rimsulfuron; however, metabolism was more rapid in the resistant lines than in the susceptible genotypes (TX430S and N223S). The percentage of recovered rimsulfuron 3 DAT corresponded to 80 and 83% in the resistant compared to 87% in the susceptible grain sorghum. At 5 DAT, metabolism was near steady in all sorghum plants but by 7 DAT, resistant genotypes metabolized 4 to 12% more than the susceptible sorghum. Rapid metabolism of rimsulfuron in ALS-resistant grain sorghum is an added mechanism that could help evaluate the level of rimsulfuron resistance.

 




INFLUENCE OF LIGHT INTENSITY IN MECHANISM OF PARAQUAT RESISTANCE IN RESISTANT (CONYZA BONARIENSIS) BIOTYPE FROM CALIFORNIA. M. L. Moretti*1, B. D. Hanson2, K. J. Hembree3, A. Shrestha1; 1California State University, Fresno, CA, 2University of California, Davis, Davis, CA, 3UCCE, Fresno, CA (297)

ABSTRACT

A glyphosate and paraquat resistant (R) biotype of hairy fleabane (Conyza bonariensis) in the San Joaquin Valley (SJV) is the first reported case of dual resistance to the aforementioned herbicides in this species worldwide.  To develop an efficient management program for this biotype, it is essential to understand the possible mechanism of resistance. Chlorophyll fluorescence (Fv/Fm) has reportedly been used as a tool to identify the mechanism of resistance in paraquat-resistant hairy fleabane and horseweed (C. canadensis). The most accepted mechanism of paraquat resistance in Conyza ssp. is sequestration into vacuoles with participation of membrane protein transporters. Therefore, the objective of this study was to measure the Fv/Fm of paraquat-treated R and susceptible (S) hairy fleabane plants under various light intensities. Potted plants at the rosette stage (16 to20 leaves) were treated with paraquat at 0.5 kg a.i.ha-1and immediately exposed to light intensities of either 0 (completely dark), 850 (medium light), or 1700 (high light) µmol m-2s-1 photosynthetic photon flux density (PPFD) in a 12 h light/dark regime for three days. Fv/Fm levels were measured at 5 min, 30 min, 1, 2, 4, 8, 12, 36, and 72h after treatment. Paraquat reduced Fv/Fm levels of all treated plants within 5 min of spraying under light presence. This reduction was more pronounced in the S plants at the higher light intensities.  The paraquat-treated S plants showed visual injury symptoms even in the completely dark treatment. The R plants were less affected by paraquat at all measurements compared to the S plants with the lowest Fv/Fm values occurring 8h after treatments at which initial recovery of the R plants was observed.  Complete recovery of the R plants, as measured by the Fv/Fm values, occurred after 36h. All R plants survived paraquat treatment regardless of light intensity but recovery was more rapid (P<0.05) under high light than at medium light or complete darkness. These findings are similar to a study in paraquat-resistant horseweed in which the authors attributed the phenomenon to paraquat sequestration into vacuoles, an energy dependent process. Such process was attributed to multidrug protein transporters, possibly including ABC transporters, which relies on ATP for active transport. Activity of these transporters was effectively lessened by selective transporter inhibitors such as potassium nitrate (KNO3).  Initial reductions in the Fv/Fm values in the R hairy fleabane plants in our study indicated that paraquat reached the chloroplasts but was inactivated soon, possibly due to sequestration. In a second study, with similar methodology, KNO3 was added to paraquat in an attempt to evaluate the effect of selective transporter inhibitors in the resistance mechanisms. Fv/Fm measurements indicated that KNO3 delayed the recovery of R plants to 36h but the plants still survived. In summary, paraquat sequestration is most likely the mechanism of resistance for this R population of hairy fleabane from the SJV, and this process is light intensity dependent. Potassium nitrate mitigated the Fv/Fm recovery process to some extent reinforcing the assumption that transporter proteins may play a role in sequestrating paraquat into metabolically inactive vacuoles.




IMPACT OF PESTICIDES ON THE NUTRITIONAL CONTENT OF FRUIT AND LEAFY TISSUE OF CROPS. G. Armel*, D. Kopsell, C. Sams, J. Vargas, R. Koepke-Hill; University of Tennessee, Knoxville, TN (298)

ABSTRACT

Pesticides are effective plant growth regulators with the potential to affect primary and secondary metabolism in labeled crops. Field, greenhouse, and laboratory studies were conducted to ascertain the impacts of POST applications of various herbicides, insecticides, fungicides, plant growth regulators, and safeners on pesticide tolerance and primary and secondary metabolites related to nutritional quality in  sweet corn (Zea mays  var. rugosa), kale (Brassica oleracea L. var. acephala), basil (Ocimum basilicum L.), and switchgrass (Panicum virgatum L.). All studies were maintained weed free and fertilized and irrigated similarly in order to understand the impact of these POST pesticide applications on nutritional content. Evaluation of nutritional quality parameters in these crops included fatty acids, elemental minerals, proteins, amino acids, carbohydrates, and carotenoid/xanthophyll antioxidants. Differences measured in nutritional quality parameters from pesticide applications will be discussed for each of the crops in the studies.



WHY ARE THERE NO NEW HERBICIDE MODES OF ACTION IN RECENT YEARS? S. O. Duke*; USDA-ARS, Oxford, MS (299)

ABSTRACT

Herbicides with new modes of action are badly needed to manage evolution of resistance of weeds to herbicides with old modes of action.   Yet, no major new mode of action has been introduced to the market place for about 20 years.  There are probably several reasons for this.  Examples of herbicides with new modes of action that have been discovered during the past two decades will be discussed.  These products may have remained dormant due to concerns that glyphosate-resistant crops have reduced the potential market for a new herbicide.  There could be other economic concerns and/or problems with toxicology with some of these products also.  Furthermore, the capture of a large fraction of the herbicide market by glyphosate with glyphosate-resistant crops led to significantly diminished herbicide discovery efforts.  This occurred as a result of consolidation and decisions among the remaining companies to put a larger portion of their discovery effort on insecticides and fungicides.  Another problem might be that the best herbicide molecular target sites may have already been discovered.  However, there are target sites that are not utilized for which there are inhibitors that are highly effective at killing plants, suggesting that this is not true.   Some of these sites may be questionable because of toxicological concerns.   Results of modern methods of target site discovery (e.g., gene knock out methods), rather than herbicide discovery, have generally not been made public.  These methods have limitations such as usually completely knocking out production of a gene product, whereas good herbicides generally kill without saturating a target site.  In summary, the reasons for a long dry period for new herbicide target sites are unclear, but several factors are probably involved. The economic stimulus to the herbicide industry caused by the evolution of herbicide-resistant weeds, especially glyphosate-resistant weeds, may result in one or more new modes of action becoming available in the not too distant future.




QSAR AND QSPR IN HERBICIDE DISCOVERY. R. D. Clark*; Simulations Plus, Inc., Lancaster, CA (300)

ABSTRACT

Quantitative structure-activity relationships (QSAR) and quantitative structure-property relationships (QSPR) have been used to guide herbicide discovery and development since the work of Toshio Fujita and Corwin Hansch in the early 1960s, and they remain relevant to series optimization and the identification of “lead hops” today.  Much about QSAR has changed since then, but many of the fundamental challenges remain the same: getting good data to work with, identifying which descriptors to use, and constructing models that produce testable hypotheses.  While many new descriptors and modeling methods have been introduced, advances in the interpretation and assessment of models are equally important. Awareness of the need for external test sets to evaluate predictive power has grown, along with an awareness of the potential hazards of straying outside a model’s applicability domain.  Last but not least, the types of properties modeled have expanded dramatically: today it is every bit as important to be able to confidently predict environmental and toxicological endpoints as it is to predict herbicidal potency.




HIGH THROUGHPUT SCREENING AND FOLLOWUP ON ENZYMES OF THE NON MEVALONATE PATHWAY. M. C. Witschel*; BASF, Ludwigshafen, Germany (301)

ABSTRACT

 

High Throughput Screening and Followup on Enzymes of the Non Mevalonate Pathway

M. C. Witschel*; BASF SE, Ludwigshafen, Germany

In the last two decades a new biosynthetic pathway for the synthesis of isoprenoids in the chloroplasts of plants has been identified, the Non Mevalonate Pathway or Methylerythritol Phosphate (MEP) Pathway. Most of the steps in this pathway have been proven to be essential for plant growth either by herbicidal inhibitors like Ketoclomazone or Fosmidomycin, or by antisense experiments. At BASF several enzymes of this pathway have been tested for inhibitors in the in vitro high throughput screening and by structure based design. Results of these screenings and the subsequent structure based optimization programs will be discussed and the identified herbicidal leadstructures will be presented.




APPROACHES TO THE USE OF NATURAL PRODUCTS FOR HERBICIDE DISCOVERY. F. E. Dayan*; USDA-ARS, University, MS (302)

ABSTRACT

The number of molecular target sites inhibited by commercial herbicides has remained essentially unchanged since the introduction of the p-hydroxyphenylpyruvate dioxygenase inhibitor sulcotrione in 1993.   Most ‘new chemistries’ introduced since have simply been molecules belonging to new chemical classes with known mechanisms of action. Examples of this are the pyrimidinedione herbicide saflufenacil, which inhibits protoporphyrinogen oxidase, and the sulfonylisoxazoline herbicide pyroxasulfone, which inhibits very-long-chain fatty acid elongase. 

As farmers face ever expanding problems associated with the evolution of herbicide-resistant weeds, there is a need for truly innovative classes of herbicides with new modes of action. There are undoubtedly a large number of novel structures in the vaults of the major agrichemical companies, some of which may inhibit new target sites. However, the use of natural phytotoxins is a biorational approach to herbicide discovery that capitalizes on nature’s ‘high-throughput’ (slow but over a much extended period of time) evolutionary chemical ecology selection process.   Furthermore, there is generally little overlap between the mode of action of natural and synthetic phytotoxins, which makes the study of natural products an important approach for the discovery of new target sites. 

The following approaches to the use of natural products for herbicide discovery will be presented: ethnobotanical approach where prior knowledge may suggest the existence of a putative phytotoxin; Chemical ecology approach where, for example, plant pathogens are more likely to produce phytotoxins than soil microbes; Structural approach where natural toxins may have structural similarities to enzyme substrates or reaction intermediates.   At every step, one should remember Pasteur’s quote ‘In the fields of observation chance favors only the prepared mind’ and be ready to notice that which may seem trivial to others. 




USING “PHYSIONOMICS AND METABOLOMICS” APPROACHES TO DISCOVERY OF NEW MODES OF ACTION. K. Grossmann*; BASF Agricultural Research Center, Limburgerhof, Germany (303)

ABSTRACT

Using “physionomics and metabolomics” approaches to discovery of new modes of action. Klaus Grossmann*, Johannes Hutzler, Stefan Tresch BASF SE, Limburgerhof, Germany; and Nicole Christiansen, Ralf Looser, Thomas Ehrhardt metanomics, Berlin, Germany. E-mail: Klaus.grossmann@basf.com

 

Keyword: Herbicide mode of action, metabolic profiling, physiological profiling

 

The search for novel herbicides with new sites or modes of action is an important assignment in crop protection research. However, for active compounds identified in greenhouse screens, the crucial point is to take the most efficient path to determine their target sites. In the literature today, molecular (functional genomics, transcriptomics), biochemical (proteomics), analytical (metabolomics) and physiological (physionomics) approaches are discussed. In particular, the metabolic and physiological response pattern to a herbicide can be viewed as the end result of changes elicited in the molecular and biochemical process chain. These response patterns are highly diagnostic of a herbicide´s mode of action and are therefore in the focus of this talk. At the starting point of mode of action characterization, we use an array of “functional” biotests for comprehensive physiological profiling of herbicidal effects. Together with a set of assays of known target enzymes, this physionomics procedure enables to discriminate known, novel or multiple modes of action of a compound. Moreover, a first clue to a new mode of action is provided with respect to which structural cell component or metabolic pathway a compound is affecting. In the latter case, metabolic profiling (metabolomics) is performed with the use of treated duckweed (Lemna paucicostata) plants. After plant extraction and subsequent GC-MS and LC-MS/MS analyses, changes in tissue levels of ca. 200 identified and 300 unknown analytes are quantified, relative to control. Check for assignment of metabolite changes to profiles of about 150 herbicides from 60 known modes of action is performed with the use of multivariate statistical data analyses. Effects on plant metabolism are visualized in detail in a biochemical pathway view. Distinct metabolite changes in a pathway (“metabolite hot spots”) can direct to the affected enzymatic step and trigger subsequent studies for target identification. Here, metabolite feeding in Lemna and molecular (e.g. mutant resistance screening) and biochemical (e.g. enzyme activity testing) methods are used. The value of this cascade strategy in mode of action identification is exemplified by recent studies on cinmethylin and isoxazoline derivatives including methiozolin, inhibitors of tyrosine aminotransferase as a new herbicide target.




CHEMICAL GENETIC APPROACHES TO HERBICIDE DISCOVERY. T. A. Walsh*; Dow AgroSciences, Indianapolis, IN (304)

ABSTRACT

Chemical genetics can be defined as the systematic use of chemical compounds as probes to elicit defined phenotypes in biological systems of interest, equivalent to genetic screening for mutant phenotypes. We have used this approach in herbicide lead discovery to uncover novel in vivo-active chemistries with excellent lead attributes, coupled with their cognate target sites. The “chemistry-first” paradigm of this approach can circumvent many of the obstacles that arise from trying to develop herbicide leads from in vitro biochemical screening of new but often chemically-unvalidated target sites. The chemical genetic approach also has advantages over classic undirected whole plant screens that can generate in vivo actives, but with no associated target site information or with poor herbicide lead attributes. Several examples of a chemical genetic approach successfully applied to herbicide lead discovery will be described, as well as some of the ensuing advantages and challenges.




IMPACT OF TILLAGE INTENSITY, POST-HARVEST RESIDUE MANAGEMENT, AND HERBICIDE PLACEMENT ON BERMUDAGRASS INTERFERENCE IN SUGARCANE. C. D. Dalley*, E. P. Richard, Jr., R. P. Viator; USDA-ARS, Houma, LA (305)

ABSTRACT

Bermudagrass is a difficult to manage perennial weed ubiquitous to Louisiana sugarcane fields. Studies conducted near Houma, LA, evaluated the impact of crop management practices on the spread of bermudagrass and sugarcane production. Three tillage frequencies were compared: standard tillage, reduced tillage, and no-till. Standard tillage, using a rolling disk cultivator, included four tillage applications: mid-March, mid-April following fertilizer injection, mid-May and early-June. Reduced tillage had two tillage applications: following fertilizer injection and in early-June. In no-till, there was no additional tillage after the crop was planted. Green harvesting sugarcane deposits 13 to 22 Mg/ha of extraneous leaf materials uniformly onto sugarcane fields. In Louisiana’s climate, this post-harvest residue has been shown to be detrimental to the growth and establishment of subsequent ratoon crops and its removal is recommended; accomplished mostly through burning. Three post-harvest residue management practices were compared: no residue removal, removal by burning, and removal from the row top with a rotating brush, moving residue into the wheel furrow. Band-application of herbicides in early-spring, in combination with row side tillage, is a common practice in Louisiana sugarcane production due to its cost savings. However, reducing tillage frequency, when combined with band-application, may increase spread of bermudagrass. Two spring herbicide application methods [metribuzin (2.8 kg ai/ha) plus pendimethalin (2.8 kg ai/ha)] were compared: broadcast-application, band-application; both were compared to no herbicide application. Bermudagrass infestations were visually evaluated in the ratoon crops. Cultivation and herbicide application method interacted in their impact on bermudagrass infestation. Under conventional tillage practices, broadcast- and band-applications had similar bermudagrass cover in the first (16 and 17%) and second ratoons (13 and 14%), with slightly higher percent cover in banded (22%) verses broadcast (15%) in the third ratoon. Bermudagrass cover was greatest under no-till for all herbicide application methods, and was more than 90% cover when no herbicide was applied. Banding herbicides, combined with reduced tillage, resulted in higher bermudagrass cover compared to standard tillage in all three ratoon crops. Post-harvest residue management did not affect bermudagrass cover. It was hypothesized that retaining the residue may protect the bermudagrass from freezing winter temperatures allowing it to resume growth earlier than when residue was removed and/or that the residue may interfere with herbicide applications. The results of this study do not support either theory. Sugar yields were affected by all three management practices, with an interaction between cultivation and herbicide applications. In plant cane, yields were less only under the combination of no-till and no herbicide application. In the ratoon crops, banding herbicides only resulted in lower yields under no-till, while reduced tillage only resulted in lower yields when no herbicide was applied. With few exceptions, reduced and standard tillage had similar yields. Yields were always lower when using no-till. When no-till was practiced, total yields for the crop cycle were reduced 11% when herbicides were applied broadcast, 15% when banded, and 25% when no herbicide was applied. When post-harvest residues were not removed yields were reduced 5, 6, and 10% in the first, second, and third ratoon, respectively, compared with removal by burning; removal by brushing was intermediate. Reducing the frequency of tillage from four to two applications appears to be a viable option for growers, even when band-applying herbicides, although adopting a no-till strategy in sugarcane seems less viable.



GLYPHOSATE APPLICATION TIMING(S) AND TANK MIXES FOR WEED CONTROL AND RESISTANCE MANAGEMENT IN GLYPHOSATE-RESISTANT SUGAR BEET. A. Anand*1, P. Jha2, J. O. Garcia2; 1Montana State University, Bozeman, MT, 2Montana State University, Huntley, MT (306)

ABSTRACT

Field experiments were conducted at the Southern Agricultural Research Center in Huntley, MT, in 2008 and 2010 to evaluate glyphosate timing and tank-mixes for weed control in glyphosate-resistant sugar beet.  Glyphosate-resistant sugar beet variety “BTS 36RR50 Pro 200” was planted on April 25, in 2008 and April 21, in 2010 at a seeding rate of 119,548 seeds/ha in 61-cm wide rows.  Weeds present at the experimental sites in both years were wild buckwheat, redroot pigweed, green foxtail, common lambsquarters, and common mallow.  Treatments were arranged in a randomized complete block design with four replications.  Treatments included three sequential applications of glyphosate at 0.84 kg ae/ha applied alone or tank-mix with other herbicides at 2-, 6-, and 8- to 10-leaf stages of glyphosate-resistant sugar beet.  Tank mixtures with glyphosate included triflusulfuron (Upbeet) at 0.002 kg ai/ha, ethofumesate (Nortron) at 0.105 kg ai/ha, or desmedipham + phenmedipham + ethofumesate (Progress) at 0.126 kg ai/ha applied at the 2-leaf stage or clopyralid (Stinger) at 0.197 kg ai/ha, clethodim (Select) at 0.157 kg ai/ha, S-metachlor (Dual II Magnum) at 1.400 kg ai/ha or dimethenamid (Outlook) at 0.840 kg ai/ha applied at the 6-leaf stage.  Glyphosate was applied alone at the 8- to 10-leaf stage.  All glyphosate applications included 20 g/L of AMS.  Herbicides were applied with a hand-held boom calibrated to deliver 94 L ha-1 at 276 kPa.  A non-treated control was included for comparison.  Crop injury and weed control were visually rated at 7, 14 and 21days after each application on a scale of 0 (no control or injury) to100 (complete control or plant death).  Two central rows in each plot were harvested on October 12, 2008 and October 6, 2010 for sugar beet yields.  Sixteen sugar beet roots from each plot were randomly sampled to estimate the sugar (sucrose) yield.  Data for crop injury, weed control, and yields were subjected to ANOVA using PROC GLM in SAS.  Means were separated using Fisher’s protected LSD test at an alpha level of 0.05.  None of the herbicide treatments caused more than 5% sugar beet injury.  A single application of glyphosate (0.84 kg ae/ha) at the 2-leaf stage of sugar beet provided complete control of redroot pigweed and green foxtail 7 DAA.  Averaged across herbicide treatments, common mallow control 7 d after the first application of glyphosate at the 2-leaf stage was 69%, which was lower than the 99% control following two applications of glyphosate with or without tank-mix.  Irrespective of tank-mixes, two applications of glyphosate (2-leaf fb 6-leaf stage) provided 100% control of common lambsquarters compared with 86% control with a single application.  Wild buckwheat control with one and two applications of glyphosate was 66 and 83%, respectively.  Three follow-up applications of glyphosate at 2-, 6- and 8- to10-leaf stages were needed to obtain >90% control of wild buckwheat.  Sugar beet root and sugar yields did not differ across herbicide treatments, and averaged 57,295 and 10,240 kg/ha, respectively.  Season-long weed interference in non-treated plots resulted in two- to three-fold decrease in sugar beet root and sugar yields compared with glyphosate treated plots.  In conclusion, multiple (two to three) applications of glyphosate were needed for season-long weed control in glyphosate-resistant sugar beet.




DIFFERENCES IN HERBICIDE RESPONSE AMONG BARNYARDGRASS POPULATIONS FROM MISSISSIPPI. J. A. Bond*, V. K. Nandula, R. C. Bond, T. W. Eubank; Mississippi State University, Stoneville, MS (307)

ABSTRACT

Herbicide resistance in barnyardgrass (Echinochloa crus-galli) is common across the southern United States rice-growing area.  In Mississippi, propanil and quinclorac resistance has been observed since the late 1990’s.  There have been reports of imazethapyr failure in imidazolinone-tolerant rice since 2005, and complaints of poor barnyardgrass control with cyhalofop are common.  Thirty-nine percent of rice growers in Mississippi suspect resistance in barnyardgrass.  To assist in developing herbicide programs for managing barnyardgrass in rice, directed surveys are conducted each year in Mississippi to identify potential herbicide-resistant populations of barnyardgrass.  Collected samples are screened for response to bispyribac, clomazone, imazamox, imazethapyr, propanil, and quinclorac.  Results from 2007 to 2010 suggest that 45% of barnyardgrass samples collected from Mississippi rice fields are resistant to propanil, 20% are resistant to quinclorac, and 15% exhibit multiple resistance to propanil and quinclorac.  Barnyardgrass response to cyhalofop is variable in greenhouse studies, with control ranging from 58 to 97%; however, no resistant populations have been identified.  Resistance to imazethapyr, imazamox, and penoxsulam is suspected and ongoing studies are addressing this problem.  Currently, bispyribac is still effective against barnyardgrass populations collected in Mississippi.  jbond@drec.msstate.edu




SYNERGISM OF IMAZETHAPYR PLUS PROPANIL COMBINATIONS FOR RED RICE CONTROL IN CLEARFIELD RICE. E. P. Webster*, J. B. Hensley; LSU AgCenter, Baton Rouge, LA (308)

ABSTRACT

In 2009, a study was conducted on a Crowley silt loam soil at the LSU AgCenter Rice Research Station near Crowley, Louisiana to evaluate the weed control of imazethapyr with various propanil formulations. Clearfield rice ‘CL 151’ was planted and treated with imazethapyr early postemergence (EPOST) followed by late postemergence (LPOST) at 70 g ai/ha. Propanil was added at 3.36 kg ai/ha to either the EPOST or LPOST treatments. Among the various propanil formulations, control of red rice, rice yield, and net returns increased from 22 to 38%,  1460 to 2970 kg/ha, and 29 to 71%, respectively, when propanil was added EPOST, and from 9 to 29%, 730 to 1790 kg/ha, and 11 to 42%, respectively, when propanil was added LPOST.

 

In 2010, a propanil plus thiobencarb pre-mix was evaluated for the potential synergistic effects on imazethapyr. The study was conducted at the same location as previously described. Treatments consisted of an EPOST application of imazethapyr at 18, 35, or 70 g/ha, with and without the addition of propanil plus thiobencarb at 4.2 kg ai/ha followed by (fb) imazethapyr at 105 g/ha LPOST. Propanil plus thiobencarb at 2.5 qt/A fb imazethapyr LPOST, and a nontreated were added for comparison.

 

The control of red rice, broadleaf signalgrass [Brachiaria platyphylla (Munro ex Wright) R.D. Webster], barnyardgrass [Echinochloa crus-galli (L.) Beauv.], yellow nutsedge (Cyperus esculentus L.), and Indian jointvetch (Aeschynomene indica L.) were visually evaluated at 0 to 100%, where 0% equals no control, and 100% equals complete plant death. Ratings were taken at 14 and 35 days after (DA) EPOST and LPOST applications, respectively. Data were evaluated using Tukey’s HSD test. The addition of propanil plus thiobencarb to imazethapyr increased the control of red rice, broadleaf signalgrass, and barnyardgrass compared with imazethapyr fb imazethapyr when imazethapyr was applied at 35 and 70 g/ha at 14 DAEPOST, and 35 and 70 g/ha at 35 DALPOST. The addition of propanil plus thiobencarb to imazethapyr increased the control of yellow nutsedge compared with imazethapyr fb imazethapyr when imazethapyr was applied at 1 and 2 oz/A at 14 DAEPOST. Propanil plus thiobencarb controlled Indian jointvetch with or without imazethapyr in the mixture. Furthermore, the addition of propanil plus thiobencarb to imazethapyr had no increase in control of all weeds evaluated when the imazethapyr rate was increased to 70 g/ha.

 

This study indicates that synergism exists between imazethapyr and propanil plus thiobencarb, in the control of yellow nutsedge, and the grasses evaluated in this study. However, no synergism was observed for Indian jointvetch due to the control obtained by propanil plus thiobencarb alone.




REBELEX FOR BROAD SPECTRUM WEED CONTROL IN U.S. RICE. J. D. Siebert*1, A. T. Ellis1, V. B. Langston2, R. B. Lassiter3, R. K. Mann4, D. G. Shatley5, L. C. Walton6; 1Dow AgroSciences, Greenville, MS, 2Dow AgroSciences, The Woodlands, TX, 3Dow AgroSciences, Little Rock, AR, 4Dow AgroSciences, Indianapolis, IN, 5Dow AgroSciences, Lincoln, CA, 6Dow AgroSciences, Tupelo, MS (309)

ABSTRACT

RebelEX herbicide is a pre-mixture of cyhalofop-butyl (Clincher® SF) and penoxsulam (Grasp® SC) that was commercially launched in 2010 for the postemergence control of broadleaf, grass, aquatic and annual sedge weeds in both drill and water seeded rice.  The labeled rate range for RebelEX is 16 [285 g ai/ha] (equivalent to 2.0 oz of Grasp SC [35 g ai/ha] + 12 oz of Clincher SF [250 g ai/ha]) to 20 [356 g ai/ha] fluid ounces (equivalent to 2.5 oz of Grasp SC [44 g ai/ha] + 15 oz of Clincher SF [313 g ai/ha]) of product per acre.  Trials conducted from 2008-2010 evaluated weed control and crop safety with RebelEX utilizing standard small plot research techniques.  Crop safety evaluations indicate excellent rice tolerance (both conventional and hybrids) to both cyhalofop-butyl and penoxsulam alone and in the premix.  When applied postflood (after the permanent flood is established) control of AESVI, ALRPH, CNPPA, ECHCG, LEFSS and SEBEX is similar for RebelEX and equivalent rates of Clincher SF and Grasp SC.  In 2010, tank mix trials were established to evaluate weed control and crop safety of RebelEX applied with either Newpath® (imazethapyr) or Beyond® (imazamox) to determine the fit in a CLEARFIELD rice system.  No rice injury was reported with any treatment.  RebelEX, Newpath and Beyond alone or in combination provided similar control of CNPPA, CYPES and ECHCG.  Although not statistically significant, a numerical increase in LEFSS control was observed with the tank mix of RebelEX+Newpath or RebelEX+Beyond over the single entities applied alone.  SEBEX control with Newpath and Beyond applied alone was 5 and 11%, respectively, but increased to at least 85% when RebelEX was added in the tank mix.  RebelEX alone provided 90% control of SEBEX (18 fl oz/A [320 g ia/ha]).  ALRPH control with RebelEX alone or RebelEX+Newpath (80 and 83%) was statistically greater than control with Newpath alone, at 73%.  ALRPH control with RebelEX alone and in combination with Beyond was numerically greater than Beyond applied alone.  RebelEX increased the control of LEFSS, SEBEX and ALRPH when tankmixed with Newpath and Beyond, as compared to Newpath and Beyond alone.  Standard efficacy and tank mix trials confirmed the broad spectrum weed control and excellent crop safety of RebelEX demonstrating the value and fit of this herbicide in any rice weed management system.

 

®™ RebelEX, Grasp, and Clincherare trademarks of Dow AgroSciences, LLC. 

®™ CLEARFIELD, Newpath, and Beyond are trademarks of BASF Corporation.

RebelEX is not registered for sale or use in all states.  Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.  Always read and follow label directions.




SHADE AVOIDANCE: THE IMPORTANCE OF PLANT-TO-PLANT VARIABILITY. C. J. Swanton*1, E. Page1, P. Westra2, M. Loux3, A. Dobbels3, K. L. Smith4, J. Bullington4, H. Wright5, C. L. Foresman6; 1University of Guelph, Guelph, ON, 2Colorado State University, Fort Collins, CO, 3The Ohio State University, Columbus, OH, 4University of Arkansas, Monticello, Monticello, AR, 5Syngenta Crop Protection Canada Inc, Guelph, ON, 6Syngenta, Greensboro, NC (310)

ABSTRACT

Recent improvements in the yield of maize have been attributed primarily to greater hybrid stress tolerance.   The genetic improvement associated with stress tolerance has been accompanied by a decrease in plant–to –plant variability observed under field conditions. The degree to which plant-to plant variability can change will be influenced by environmental stresses as well as the way in which we use herbicide technology.  Evidence will be presented to illustrate the importance of understanding how timing of herbicide application can increase plant-to-plant variability and thereby potentially reduce the stress tolerance of a maize hybrid. In addition to yield, plant-to plant variability should be taken into consideration when defining the application timing for new herbicide technology. 




PYROXASULFONE:PROFILE OF NEW HERBICIDE FOR RESIDUAL WEED CONTROL. Y. Yamaji*1, H. Honda1, M. Kobayashi2, O. Watanabe2; 1Kumiai America, White Plains, NY, 2Kumiai Chemical Industry, Tokyo, Japan (311)

ABSTRACT

A new herbicide, pyroxasulfone is being developed in the United States, Australia and Canada.  Joint review is ongoing by the respective country’s regulatory agencies.  The chemical structure, consisting of two hetero rings results in unique physical/chemical properties, a favorable environmental and toxicological profile, and preemergence weed control with wide application windows.  Pyroxasulfone can be used in corn, soybean and wheat with a key feature being residual control.  Pyroxasulfone provides consistent, season long weed control of grass and small seeded broadleaf weeds such as Italian ryegrass and Common waterhemp.  The mode of action, inhibition of very long chain fatty acid elongase, works to control current herbicide resistant weeds.  Fall, preemergence application on winter wheat provides excellent Italian ryegrass control through to spring.  Spring application will provide Common waterhemp control up to 8 weeks at proposed use rates.  Several products including pre-mixes containing pyroxasulfone will be available.



UTILITY OF PYROXASULFONE FOR RESIDUAL WEED CONTROL IN CORN AND SOYBEAN. W. E. Thomas*1, J. S. Harden1, R. Bond1, S. J. Bowe1, R. A. Liebl1, Y. Yamaji2, H. Honda2, T. Ambe3; 1BASF Corporation, Research Triangle Park, NC, 2Kumiai America, White Plains, NY, 3Kumiai Chemical Industry, Tokyo, Japan (312)

ABSTRACT

Pyroxasulfone is a selective herbicide under development for residual control of grass and small seeded broadleaf weeds in conventional and herbicide-tolerant corn and soybean production. Field research trials have been conducted across the US to evaluate weed control and crop safety from various application timings including fall, early preplant, preplant, preemergence, and postemergence. Rate ranges of pyroxasulfone have been tested for various soil types and application timings; with tested rate ranges being 94 to 157, 125 to 188, and 157 to 220 g ai/ha on coarse, medium, and fine textured soils, respectively. Combined with the flexible application timings and length of residual weed control, studies indicate that pyroxasulfone will provide an effective solution for many problematic weeds including Setaria spp. and glyphosate-resistant Amaranthus spp. Similar to other group K3 herbicides, pyroxasulfone may not provide complete control of some weeds such as common lambsquarter (Chenopodium album) and giant ragweed (Ambrosia trifida). Thus, our research indicates that a tank-mix partner or sequential herbicide system may be required to provide adequate control. Negligible corn and soybean injury has been observed from pyroxasulfone, regardless of application timing. These field trials show that pyroxasulfone provides a flexible management tool that consistently controls numerous grasses and small-seeded broadleaf weeds. Registration is anticipated in 2011.

Corresponding email: walter.e.thomas@basf.com.




MANAGEMENT OF ITALIAN RYEGRASS WITH PYROXASULFONE IN WINTER WHEAT. S. Tan*1, R. Bond1, S. J. Bowe1, R. A. Liebl1, Y. Yamaji2, H. Honda2, T. Ambe3; 1BASF Corporation, Research Triangle Park, NC, 2Kumiai America, White Plains, NY, 3Kumiai Chemical Industry, Tokyo, Japan (313)

ABSTRACT

Pyroxasulfone is a new selective herbicide under development for residual control of grass and broadleaf weeds in wheat production. Field research trials have been conducted across the USA from 2005 to 2009 to evaluate Italian ryegrass control and wheat safety from different application timings including preplant, preemergence, and postemergence. Rate ranges of pyroxasulfone from 25 to 250 g ai/ha have been tested for different application timings. Studies indicate that pyroxasulfone provides excellent control of Italian ryegrass and some other winter annual weeds with flexible application timing and long-lasting efficacy. No or little crop response was observed from most of the weed-free trials. These field trials show that pyroxasulfone can be an effective management tool for Italian ryegrass and other grass and broadleaf weeds in winter wheat.




EVALUATION OF PYROXASULFONE FOR GRASS WEED MANAGEMENT IN WINTER WHEAT IN WESTERN OREGON. A. G. Hulting*, B. Hinds-Cook, D. Curtis, C. Mallory-Smith; Oregon State University, Corvallis, OR (314)

ABSTRACT

Pyroxasulfone (KIH-485) is a Group 15, soil-applied herbicide that has the potential to control many broadleaf and grass weed species in several crops including winter wheat.  The mode of action of pyroxasulfone has been reported to be similar to that of other inhibitors of very-long-chain fatty acid synthesis.  A series of field experiments were conducted during 2006-2009 near Corvallis, OR, to evaluate the potential for Italian ryegrass control in winter wheat with preemergence and early postemergence applications of pyroxasulfone.   Application rates of pyroxasulfone evaluated ranged from 0.05 kg ai/ha to 0.15 kg ai/ha.  Early postemergence treatments were generally applied during late fall at the 1 to 3 leaf growth stage of winter wheat which corresponded with 1 to 2 leaf Italian ryegrass.  All of the pyroxasulfone treatments were compared to current Italian ryegrass soil-applied chemical control programs in winter wheat which included the use of herbicides such as diuron, flufenacet, flufenacet +metribuzin and diclofop.  Visual evaluations of percent Italian ryegrass control and winter wheat injury were made at regular intervals following applications.  Winter wheat yields were quantified at grain maturity.  Percent Italian ryegrass control following pyroxasulfone applications ranged from 65 to 100 % and was equal to control achieved with flufenacet and flufenacet +metribuzin treatments and greater than that achieved with diuron applications in most studies.  In general, the highest rates of pyroxasulfone evaluated resulted in the greatest control of Italian ryegrass.  Percent winter wheat injury from pyroxasulfone ranged 0 to 10 % and was associated with the higher application rates evaluated and preemergence application timings. No yield loss in winter wheat from any of the pyroxasulfone treatments and timings was quantified. Pyroxasulfone, when applied at the rates and timings in these studies, appears to have a unique fit as a soil-applied grass weed management herbicide in winter wheat in western Oregon based on its high level of activity on grass weed species such as Italian ryegrass and excellent crop safety.




IMPACT OF VOLUNTEER ROUNDUP-READY CORN IN WHEAT-CORN-FALLOW. A. Schlegel1, B. D. Olson2, J. D. Holman*3; 1Kansast State University, Tribune, KS, 2Dow AgroSciences, Geneva, NY, 3Kansas State University, Garden City, KS (315)

ABSTRACT

A common crop rotation in the west central Great Plains was no-till winter wheat-corn-fallow. Most of the corn produced was herbicide tolerant, and volunteer corn in fallow was not controlled with glyphosate. This study evaluated the impact of volunteer corn on soil moisture storage in fallow and the succeeding winter wheat crop across three locations in western Kansas between 2008 and 2010. Volunteer corn reduced available soil water at wheat planting 8 out of 9 site years. On average, available soil water was reduced by 1 in for each 2500 volunteer corn plants acre-1. Volunteer corn reduced wheat tillers in half of the site years. Similarly, volunteer corn reduced wheat yields in half of the site years, and yields were reduced 1 bu acre-1 for every 500 volunteer corn plants acre-1. When wheat yields were above 70 bu acre-1 or below 35 bu acre-1 other factors affected wheat yield more than the preceding volunteer corn population or available soil water at wheat planting.




EMPIRICAL INSIGHTS INFORM A SPATIALLY EXPLICIT INVASIVE SPECIES MODEL. E. Rauschert*, D. A. Mortensen; The Pennsylvania State University, University Park, PA (316)

ABSTRACT

 Preventing or slowing the spread of invasive species into new areas is an important part of invasive species management, as eradication is usually not feasible once populations are well-established. Although in most cases, human activities are thought to be the primary drivers of long-distance dispersal, quantification of the vectors involved has been lacking in many cases. We present a the results of long-distance dispersal experiments to understand the rapid spread in North America of the invasive exotic Microstegium vimineum (Japanese stiltgrass) at local and regional scales. We use the information gained in the dispersal experiments to model the long-distance spread of the species through a forest landscape. Detailed small-scale experiments provide the data to model the natural spread of Microstegium using maximum likelihood techniques. These models predict dispersal parameters ranging from 0.18 m to 1.86 m, depending on the habitat, which imply spread rates several orders of magnitude slower than actual large-scale observations. Forested roads, along which Microstegium grows abundantly, are often unpaved and are subject to frequent maintenance activities such as road grading. Experiments using seed proxies document the ability of road grading to rapidly spread seeds throughout road networks, with some seed proxies traveling over 250 m in a single event. The resulting simulations mimic the actual invasion pattern observed when facilitated movement along roads is incorporated. These results highlight the need to explicitly address human-mediated spread, often from multiple vectors, when managing invasive species, as this likely determines the speed of an invasion, rather than the natural dispersal abilities of the species.




ECOLOGY, BIOLOGY AND CONTROL OF EXOTIC-INVASIVE WEEDS IN COASTAL FORESTRY OF BRITISH COLUMBIA, CANADA. R. R. Prasad*; Pacific Forestry Centre, Victoria, BC (317)

ABSTRACT

Scotch broom (Cytisus scoparius), Gorse (Ulex europaeus) Daphne (Daphne laureola) and English ivy (Hedera helix), are four prominent, invasive plants that pose a serious threat to Garry oak and associated ecosystems on federal lands in Victoria, British Columbia. These plants colonize disturbed areas quickly, form dense monospecific stands, remain persistent for a long time and defy any easy eradication program. They suppress and inhibit the growth of native plants and ultimately arrest forest succession. Several federal departments including the Department of Environment, Department of National Defence, Department of Fisheries and Oceans, Department of Indian Affairs and Parks Canada have expressed great concerns regarding their rapid incursion, adverse impacts and the resulting degradation of native habitats. With a grant from the Department of Environment and the Department of National Defence, we conducted research to examine the population dynamics, phenology and control methods of these invasive plants on federal lands near Victoria, B.C. Of the several methods of control tested, including manual cutting, application of a registered herbicide (Release- triclopyr), a fungal bioherbicide (Chondrostereum purpureum), and a commercial plastic mulch, it was found that some treatments (mulch and herbicide) provided 100% efficacy on resprouting behaviour of all four invasive species. While one bioherbicide (Fusarium tumidum) was very effective on Scotch broom under the greenhouse conditions, it was not applied under field conditions. The other bioherbicide (Chondrostereum purpureum) produced a variable response when applied under the field conditions. Manual cutting was found to be the least effective. Also a novel prospective bioagent (Phomopsis sp. denovo) was isolated from dying and dead samples of Daphne from the field and results from laboratory, greenhouse and field conditions suggest that it may hold great potential for control of Daphne. Continued and additional research is necessary to determine the appropriate formulations of these bioagents as well as the effectiveness of the different and integrated control treatments over a period of years. A new technology using superheated water (Aquacide) to kill vegetative shoots of gorse did not offer long term control nor was it found to be cost effective.




SURVEY OF INVASIVE PLANTS ON GUAM AND IDENTIFICATION OF THE 20 MOST WIDESPREAD. G. P. Reddy*; University of Guam, Mangilao, GU (318)

ABSTRACT

Invasive plants are introduced, nonnative species that thrive and spread spontaneously in areas beyond their natural range.  They are characteristically adaptable and aggressive and have high reproductive capacity.  Their vigor, combined with escape from their natural enemies, often leads to extensive outbreak populations.  The many invasive species on Guam constitute a growing problem.  A survey of invasive plants in five habitat types across the 20 municipalities of Guam identified the 20 most widespread:  The Hairy beggar's-tick or Spanish needles, Guinea grass, Blue porter weed or Jamaica vervain, Chain of love or Mexican creeper, Russell river grass, Perennial grass, Pacific island silver grass or Japanese silver grass, wild poinsettia, Mexican fireplant or milkweed, siam weed, American rope or Chinese creeper, mile-a-minute weed, cinderella weed or nodeweed, garden spurge or red milkweed, sensitive plant or sleeping grass, leadtree, mission grass or foxtail grass, dwarf poinsettia or wild poinsettia, paddy’s lucerne or common sida, balsam pear or bitter gourd, golden beardgrass or Inifuk, graceful spurge and swollen fingergrass. At present, the best option for managing them could required more work on the possibility of biological control and may be to adopt preventive and mechanical control methods.




TOP 10 WORST HERBICIDE RESISTANT WEEDS GLOBALLY. I. M. Heap*; WeedSmart, Corvallis, OR (319)

ABSTRACT

The evolution of herbicide-resistant weeds continues to threaten the sustainability of global agriculture. Herbicide resistance is the evolved capacity of a previously susceptible weed population to withstand a herbicide and complete its lifecycle when the herbicide is used at normal rates in an agricultural situation. Through rare random genetic mutations, weed populations can naturally contain herbicide-resistant individuals at very low frequencies. Weeds may resist herbicides through an altered target site, enhanced metabolism, decreased translocation, or increased sequestration. Repeated use of the same herbicide, or herbicide mode of action, eventually enriches the frequency of these rare mutations to a point where they predominate and cause herbicide failure. The first documented case of a herbicide resistant weed was that of triazine-resistant Common Groundsel (Senecio vulgaris) found in 1970 in the USA.   The International Survey of Herbicide Resistant Weeds (www.weedscience.org) documents the occurrence of herbicide-resistant weeds worldwide. The survey currently documents 350 different herbicide-resistant weed biotypes in 59 countries and they continue to increase at a rate of about 9 new biotypes per year. Many of these cases are scientific curiosities rather than major agronomic problems. Of the top 20 most widespread and economically important herbicide-resistant weed species, ten are grasses, and five are pigweed species (Amaranthus spp.). The most problematic species worldwide is Lolium rigidum, which has been identified as resistant in twelve countries, has evolved resistance to eleven MOAs, occurs in eight cropping regimes and infests over 20,000 farms and 4 million acres. Avena fatua, Amaranthus spp.,Conyza spp., Echinochloa spp., Chenopodium album, and Kochia scoparia the next most important herbicide-resistant weeds, globally. Since the mid-1990’s the use of glyphosate in glyphosate-resistant crops has been extremely valuable in controlling existing herbicide-resistant weeds that evolved resistance in conventional crops. Glyphosate provides excellent control of ALS inhibitor, ACCase inhibitor, and triazine resistant weeds that had become serious problems in corn/soybean rotations and cotton production. However over reliance on glyphosate for weed control led to a rapid increase in the number of glyphosate-resistant weeds (21 globally). Whilst Conyza canadensis is the most widespread glyphosate-resistant weed, glyphosate resistant pigweed species, in particular Amaranthus palmeri and Amaranthus rudis, pose the biggest threat to the sustainability of glyphosate-resistant crops. Other serious threats are posed by Ambrosia spp., Lolium spp., and Sorghum halepense. The sustainability of both conventional and glyphosate-resistant crops is dependent on rotation of herbicide modes of action in conjunction with integrated weed management practices.

 




GEOGRAPHICAL DISTRIBUTION OF ACCASE INHIBITOR RESISTANT ECHINOCHLOA SPECIES IN RECLAIMED PADDY FIELDS, SEOSAN, KOREA. D. Kim, S. Lim*, M. Park; Seoul National University, Seoul, South Korea (320)

ABSTRACT

This study was conducted to investigate the geographical distribution of ACCase inhibitor resistant E. crus-galli in Seosan, where acetyl CoA carboxylase (ACCase) inhibitor resistant Echinochloa crus-galli var. crus-galli was first found in 2007. In 2008, we collected Echinochloa crus-galli seeds from 158 sites of Seosan Hyundai reclaimed paddy fields with an area of 10,000 ha. Whole-plant dose-response studies were conducted to evaluate the extent of cyhalofop-butyl resistance of all the collected accessions. Echinochloa crus-galli plants of all the accessions were tested at the 4 leaf stage with cyhalofop-butyl at a range of doses, 0, 62.5, 125, 250, 500 g a.i. ha-1. Among 158 accessions, 119 accessions showed resistance to cyhalofop-butyl with R/S ratio of greater than 10 and evenly distributed in the fields. The average R/S ratio is 23.6 with one accession showing significantly high resistance with R/S ratio of 47.2. GIS mapping of R/S ratio and E. crus-galli plant density showed that the resistant E. crus-galli is now evenly and wide spread in the fields with high dispersal potential.




ALS INHIBITOR RESISTANT ECHINOCHLOA SPECIES EVOLVED IN KOREAN PADDY FIELDS. D. Kim*, S. Kang, M. Yook, J. Song; Seoul National University, Seoul, South Korea (321)

ABSTRACT

 A series of herbicide dose-response studies were conducted to investigate ALS inhibitor resistance in Echinochloa crus-galli and E. oryzicola collected in Korean rice paddy fields. Echinochloa crus-galli collected from Seosan, Gimje, and Suwon and E. oryzicola collected from Gimje, Iksan, Naju, and Suwon in Korea were tested with different acetolactate synthase (ALS) inhibitors with different chemistries, azimsulfuron (sulfonylurea), penoxulam (triazolo pyrimidine), pyriminobac-methyl (pyrimidinyl benzoate) to evaluate their resistance to ALS inhibitors. The R/S ratio of Echinochloa crus-galli Seosan-5 accession, which was confirmed to be resistant to ACCase inhibitor cyhalofop-butyl, was 5.40, 3.40 and 1.39 for azimsulfuron, penoxulam and pyriminobac-methyl, respectively. This result implies that the resistance to ALS inhibitors depends on their chemistry. Similar results were also found in Echinochoa oryzicola Gimje and Iksan accessions, which also showed resistance to cyhalofop-butyl, with the greatest R/S ratio for azimsulfuron, followed by penoxulam and pyriminobac-methyl. Therefore, it can be concluded that Echinochloa species showing resistance to cyhalofop-butyl also showed resistance to ALS inhibitors with the greatest resistance against sulfonylurea and the least against pyrimidinyl benzoate. Further works are now in progress to investigate resistance mechanism and reason of such difference in ALS resistance depending on chemistry.




STATUS OF GLYPHOSATE-RESISTANT ITALIAN RYEGRASS IN MISSISSIPPI. R. C. Bond*, V. K. Nandula, J. A. Bond, T. W. Eubank; Mississippi State University, Stoneville, MS (322)

ABSTRACT

Italian ryegrass has become increasingly problematic for growers in the Mississippi Delta since 2005.  Two Italian ryegrass populations from Mississippi, Tribbet (T) and Fratesi (F), were suspected to be tolerant to glyphosate.  Both suspected resistant populations were screened for glyphosate resistance.  A susceptible (S) population from Elizabeth, Mississippi (E) was included for comparison.  Plants were treated with isoproylamine salt of glyphosate at 0, 0.11, 0.21, 0.42, 0.84, 1.68, 3.36, and 6.72 kg ae/ha. GR50  values for T, F, and E populations were 0.66, 0.66, and 0.22 kg/ha, respectively, indicating that the T and F populations were threefold more tolerant to glyphosate compared to the E population. 

 

Laboratory experiments were also conducted to characterize the mechanism of glyphosate tolerance in the two glyphosate resistant populations.  The Tribbet population absorbed less of the applied 14C-glyphosate (43%) compared to the susceptible (E) population (59% of applied) at 48 h after treatment (HAT).  The Fratesi population absorbed 56% of the applied 14C-glyphosate 48 HAT which was similar to both the T and E populations, but tended to be more comparable to the E population.  The amount of 14C-glyphosate that remained in the treated leaf was significantly higher than the T (67% of absorbed) and F (65% of absorbed) populations compared to the E population (45% of absorbed) at 48 HAT.  There were no differences in epicuticular wax mass among the three populations.  Shikimate acid accumulated rapidly at higher levels in glyphosate-treated leaf segments of the S populations compared to the T population up to 100 µM glyphosate.  However, above 500 µM glyphosate, the levels of shikimate were similar in both the T and E populations.  No degradation of glyphosate to tolerance to glyphosate in the T population is partly due to reduced absorption and translocation of glyphosate and in the F population it is partly due to reduced translocation of glyphosate.

 

Information regarding the influence of environmental factors of germination and emergence of glyphosate-resistant (GR) Tribbet Italian ryegrass population was needed to understand of the biology and ecology and to aid in management of this resistant weed species.  Experiments were also conducted to determine the effects of temperature, light, pH, salt, and osmotic stress and planting depth on germination of T and glyphosate-susceptible Elizabeth Italian ryegrass populations.  Overall, germination of both populations of Italian ryegrass was highest at 13° C and decreased when temperature increased to 20 or 27° C under both light and dark conditions.  Light stimulated germination (57%) compared to darkness (41%) at 13° C, but light had no effect on germination at 20 and 27° C.  The GR Italian ryegrass population had higher germination (69-87%) compared to the E Italian ryegrass population (37-57%) at pH range of 4-7.  Seedling emergence was less than 7% from seed planted at 0.5 cm depth and no seedlings emerged from seed planted below 2.5 cm for both populations.  Both populations germinated under a broad range of environmental conditions used in the study, however, the T populations was higher than the E population. 

 

A survey of GR Italian ryegrass was also conducted to document the distribution GR populations in Mississippi.  Seed samples suspected to be resistant to glyphosate were collected from 17 counties in the Mississippi Delta region.  Greenhouse studies were conducted to screen for resistance to glyphosate at 0.84 kg ae/ha.  Among 100 Italian ryegrass populations, one-third was considered to be resistant to glyphosate with at least one resistant population in 12 counties.  Additional greenhouse experiments were conducted to screen for resistance to preemergence and postemergence herbicides  Preemergence herbicides screened included S-metolachlor, clomazone, trifluralin, and chlorimuron-ethyl plus tribenuron-methyl.  Postemergence herbicides included diclofop, mesosulfuron, and pyroxsulam.  There were one or more Italian ryegrass populations resistant to chlorimuron ethyl plus tribenuron methyl, diclofop, mesosulfuron, and pyroxsulam.



GROWTH AND FITNESS OF GLYPHOSATE-RESISTANT GIANT RAGWEED. C. B. Brabham*, W. G. Johnson; Purdue University, West Lafayette, IN (323)

ABSTRACT

   Glyphosate resistance in giant ragweed has been confirmed in nine US states and in Ontario, Canada. Glyphosate resistance in giant ragweed is poorly understood and it is not known if resistance is associated with a fitness penalty in the absence of glyphosate. Field studies were conducted to compare the vegetative and reproductive productivity of a glyphosate-resistant (GR) and –susceptible (GS) giant ragweed in a non-competitive environment. Both biotypes had similar growth patterns for height gain and accumulation of leaf area and shoot dry weight over the 50 day experiment. At the six weekly harvest intervals, GR were greater than or equal to GS in height, leaf area, and shoot dry weight. As the season progressed, GR transitioned to reproduction earlier and shed pollen eight days before GS in both years. At physiological maturity, GR produced 1,125 seeds plant-1, while GS produced 1,493 seeds plant-1 and allocated more stored energy to seeds. These finding suggest glyphosate resistance in giant ragweed is associated with a fitness penalty.   




STUDIES ON GLYPHOSATE RESISTANT GIANT RAGWEED IN ONTARIO. J. Vink1, F. J. Tardif*2, P. H. Sikkema1, D. E. Robinson1, M. B. Lawton3; 1University of Guelph, Ridgetown, ON, 2University of Guelph, Guelph, ON, 3Monsanto Canada, Guelph, ON (324)

ABSTRACT

Giant ragweed (Ambrosia trifida) is an extremely competitive weed and is becoming an increasing problem for soybean growers in southwestern Ontario. In 2008, a giant ragweed biotype near Windsor, ON was not controlled with glyphosate and further testing confirmed it as the first glyphosate resistant weed in Canada.  Giant ragweed seed was collected from 65 fields across Essex, Kent and Lambton counties to document the distribution of glyphosate resistant giant ragweed in Ontario. Giant ragweed seedlings were sprayed with glyphosate at 1800 g ae/ha, and evaluated 1, 7, 14 and 28 days after application. Preliminary results from the greenhouse testing indicate there are additional fields in southwestern Ontario with glyphosate resistant giant ragweed. Field trials in soybean were initiated during the summer of 2010 at three locations in Essex County with known glyphosate resistant giant ragweed. The objectives were to determine the level of giant ragweed control with higher rates of glyphosate, glyphosate tank mixes applied preplant and glyphosate tank mixes applied postemergence.  Based on the first year of field trials, there are only two glyphosate tank mixes applied preplant that provided acceptable control of glyphosate resistant giant ragweed. Glyphosate (900 g ae/ha) + 2, 4-D ester (500 g ai/ha) and glyphosate (900 g ae/ha) + saflufenacil (25 g ai/ha) provided 97% and 87% control 4 weeks after application, respectively. Giant ragweed control with higher rates of glyphosate was not satisfactory. The recommended field rate (900 g ae/ha) provided only 31% control, while some giant ragweed plants were able to survive glyphosate applied at 10,800 g ae/ha or 12 times the recommended field rate. Use of dicamba with Dicamba tolerant soybeans was very effective controlling glyphosate resistant giant ragweed at the one confined field trial location where it was tested.




A MODELLING APPROACH FOR UNDERSTANDING THE RISKS OF BARNYARDGRASS EVOLVING RESISTANCE TO HERBICIDES IN RICE. M. V. Bagavathiannan*1, J. K. Norsworthy1, K. L. Smith2, P. Neve3; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas, Monticello, Monticello, AR, 3University of Warwick, Wellesbourne, England (325)

ABSTRACT

A modeling approach for understanding the risks of barnyardgrass (Echinochloa crus-galli) evolving resistance to herbicides in rice. Muthukumar V. Bagavathiannan*, Jason K. Norsworthy, University of Arkansas, Fayetteville, AR; Kenneth L. Smith, University of Arkansas, Monticello, Monticello, AR; and Paul Neve, University of Warwick, Wellesbourne, United Kingdom.

Rice is an important crop in Arkansas, comprising about 47% of the total U.S. rice acreage and 46% of total U.S. rice production.  Barnyardgrass is the most problematic weed of rice in Arkansas, and it is typically managed using herbicides. Extensive use of herbicides in rice production has led to the evolution of barnyardgrass resistance to major rice herbicides. Currently, barnyardgrass resistance globally has been confirmed for at least eight different modes of action and most of them originate from rice.  The evolution of barnyardgrass resistance to imazethapyr is of particular concern because of the widespread adoption of Clearfield® rice technology in recent years, which has favored multiple applications of imazethapyr in a growing season. Herbicide resistance simulation models are valuable in predicting and managing resistance in weed populations. For instance, the glyphosate resistance simulation models for rigid ryegrass (Lolium rigidum) in Australia and Palmer amaranth (Amaranthus palmeri) in Arkansas, U.S. were effectively utilized for making appropriate management decisions. Such models were typically developed for simulating weed resistance to a single mode of action. However, in recent years, there is occurrence of multiple resistant barnyardgrass populations in Arkansas.  There is an urgent need to understand the simultaneous evolution of resistance to more than one herbicide mode of action. In this view, a mathematical model is being developed to simulate the concurrent evolution of barnyardgrass resistance to acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibiting herbicides in rice. The risks of ALS and ACCase resistance under current management regimes are explored, and the relative effectiveness of some alternative strategies in slowing the rate of evolution of resistance is investigated. Overall, this model is a valuable tool to address important issues pertaining to herbicide resistance management in barnyardgrass. Future research will continue to refine the model incorporating new mutation, seed immigration, and crop rotation. The biological, genetic, and management assumptions for the model are presented in a separate poster presentation. muthu@uark.edu




DIFFERENTIAL TOLERANCE TO GLUFOSINATE AND HPPD INHIBITORS AMONG PALMER AMARANTH POPULATIONS. G. M. Botha*, N. R. Burgos, E. L. Alcobar; University of Arkansas, Fayetteville, AR (326)

ABSTRACT

Population differentiation in tolerance of Palmer amaranth (Amaranthus palmeri) to glufosinate and tembotrione.

George Botha, Nilda R. Burgos, and Ed Allan L. Alcober

University of Arkansas, Department of Crop, Soil and Environmental Science, USA

Palmer amaranth (Amaranthus palmeri) is a weedy amaranth, which has become one of the major weed problems in upland areas in the southern U.S. In 2005, resistance of Palmer amaranth to glyphosate was reported in Mississippi County, Arkansas. Other states in the US that had reported resistance of Palmer amaranth to glyphosate within this period include Georgia, North Carolina, South Carolina, Tennessee, and Mississippi.

The absence of desirable weed control options prompted research on alternative herbicides to glyphosate. Greenhouse experiments were therefore initiated to evaluate the tolerance of 12 glyphosate-resistant Palmer amaranth accessions to Ignite 280L (glufosinate, glutamine synthetase inhibitor) and Laudis (tembotrione, HPPD inhibitor). Each herbicide was tested at the full, ½, and ¼ doses. The experiments were conducted between October and December 2010. Plant injury and mortality were recorded 21 days after treatment (DAT).

Significant differences were observed between accessions on responses to both herbicides. Glufosinate caused 11 to 100 % injury to Palmer amaranth as the rate increased from 0.183 kg ai ha-1 (0.25x dose) to 0.73 kg ai ha-1 (full dose), while mortality ranged from 0% to 98% at this dose range. The full dose of glufosinate caused 94 to 100% injury and 76 to 98% mortality.

The Pra-C accession was most tolerant to glufosinate at both half (0.365 kg ai. ha-1) and full doses causing 49 and 94 % injury, respectively. Lee-accession was the most susceptible with 96% injury at the half dose. Differential tolerance to glufosinate was apparent at reduced doses. The full dose of tembotrione (0.08 kg ai ha-1) caused 55 to 99% injury and 16 to 96 % mortality on Palmer amaranth accessions.  Differential tolerance to this herbicide was apparent at the full dose.  Mis-B, STF-C1, and STF-B accessions were tolerant to tembotrione. 

Nomenclature: glufosinate, tembotrione; Palmer amaranth, Amaranthus palmeri S.Watts. AMAPA.

 Key words: alternative herbicides, differential tolerance, glutamine synthetase inhibitor, herbicide resistance, HPPD inhibitor, injury, mortality




TIMING THE REMOVAL OF WINTER PEAS INTERCROPPED WITH WINTER WHEAT TO OPTIMIZE AVAILABLE SOIL NITROGEN AND MOISTURE IN A DRYLAND SMALL GRAIN SYSTEM. K. A. Borrelli*, I. C. Burke, R. T. Koenig, D. R. Huggins, S. H. Hulbert; Washington State University, Pullman, WA (327)

ABSTRACT

Crop diversification is a common practice among growers interested in organic and sustainable farming practices. Wheat growers could benefit from intercropping a legume as a source of biological nitrogen (N) with the wheat if competition for other resources is not a concern. The main objective of this experiment was to determine the optimal time to mechanically remove winter pea (Pisum sativum L. cv. ‘Granger’) intercropped with winter wheat (Triticum aestivum L. cv. ‘Brundage’) to provide the greatest amount of fixed N and perhaps other benefits to the wheat crop while reducing soil moisture stress. Winter wheat and winter pea were seeded simultaneously using a 2.2 m wide double disk no-till drill on October 16, 2009 in Pullman, WA. The experiment was arranged in a 2-factor strip plot design with four replications and two controls, winter wheat alone and winter pea alone. Four removal times were determined based on percent cover of the intercrop (time 1 is 25% row canopy cover; time 2 is 50% row canopy cover; time 3 is 75% row canopy cover, time 4 is 100 % row canopy cover; and time 5 is harvest). Before removing the crop, a subsample of each crop was taken from 3 randomly selected, 25 cm lengths in the last 3 m of each treatment plot. Samples of aboveground biomass from wheat and pea were collected again from previously swept plots at each new treatment time. Soil samples were collected to a depth of 0 to 60 cm at each treatment time for treatment plots, non-intercropped controls and previously swept plots, and for all plots at harvest to a depth of 0 to152 cm. Soil samples were analyzed for gravimetric water content and inorganic N. Increasing duration of the intercrop did not affect wheat or pea growth. Soil moisture was lowest for both pea and wheat removed at 50% cover and no difference was observed in soil moisture over the other sampling times or the control. Soil N was higher in plots with peas as the main crop compared to plots with wheat as the main crop, suggesting that peas left more residual N than wheat. However, no difference was found between the treatments when wheat was removed. Higher soil N than the other treatments was observed when peas were removed at 75% cover. Results indicate that competition for soil water and N may not affect wheat growth when intercropped with a legume.  




THE IMPACT OF TWO YEARS OF WILD OAT MANAGEMENT AFTER FOUR YEARS OF LOW CROP INPUTS IN BARLEY AND CANOLA. K. N. Harker*1, S. Brandt2, J. T. O'Donovan1, R. E. Blackshaw3, E. N. Johnson2, R. Kutcher4; 1Agriculture and Agri-Food Canada, Lacombe, AB, 2Agriculture and Agri-Food Canada, Scott, SK, 3Agriculture and Agri-Food Canada, Lethbridge, AB, 4Agriculture and Agri-Food Canada, Melfort, SK (328)

ABSTRACT

Crop inputs influence weed and crop yield outcomes as well as net returns. A study was conducted at five western Canada locations (Lacombe, AB; Lethbridge, AB; Beaverlodge, AB; Scott, SK; and Melfort, SK) to determine the impact of crop input levels on weed biomass and crop yields in a barley-canola rotation with each rotation phase present each year. Inputs and their respective levels were as follows: cultivar (barley – ‘AC Metcalfe’ or ‘Harrington’, canola – ‘InVigor 5020’ or ‘84S00LL’), seeding rate (barley – 150 or 300 seeds m-2, canola – 75 or 150 seeds m-2), fertilizer rate (0, 50, or 100% of recommended), and herbicide rate (0, 50, or 100% of recommended). Higher levels of individual inputs were added to the lowest input combination and lower levels of individual inputs were removed from the highest input combination in each crop. All possible treatment combinations were not employed. The same input levels were applied to the same plots for four consecutive years. In general, high input levels were more necessary for high net returns in canola than in barley, and reduced fertilizer and herbicide inputs were most detrimental to crop yield (especially by year 3 and 4). In year five and six, full inputs in barley or RR canola were applied to respective rotational phase plots to determine “recovery” from the previous four years of cumulative treatment effects. A surprising number of plots had similar yield and weed biomass to the plots subjected to full inputs for the previous four years. The best yield recovery in year five and six low-input treatments were in plots that included 100% herbicide rates in previous years. The highest weed biomass in year five and six plots was from plots with fertilizer applied in the absence of herbicide for the previous 4 years, or from high input plots with no herbicide applied for the previous 4 years.



ENVIRONMENTAL CONDITIONS, GROWTH STAGES AND FUNGICIDES AFFECT HERBICIDE TOLERANCE OF WINTER WHEAT. M. De Jong*1, P. H. Sikkema2, F. J. Tardif1, M. Cowbrough3; 1University of Guelph, Guelph, ON, 2University of Guelph, Ridgetown, ON, 3OMAFRA, Guelph, ON (329)

ABSTRACT

Environmental conditions, growth stages and fungicides affect herbicide tolerance of winter wheat. De Jong, M., F. Tardif, P. Sikkema, and M. Cowbrough. Department of Plant Agriculture, University of Guelph, Guelph, ON

Profitable winter wheat production in Ontario is largely dependant on grain yield and as such, yield losses due to weeds and diseases will have a greater impact when crop prices are high. It is common for producers to tank-mix herbicides and fungicides to reduce application costs and save time. These applications are often made early in the season when temperatures approach freezing. In the spring of 2008, a number of producers experienced significant crop injury when they applied herbicide-fungicide tank-mixes to winter wheat. Field studies were conducted at four Ontario locations to determine the extent of crop injury and associated yield loss, and to explore whether it was due to the environmental conditions at application, the crop stage at application, or the specific combination of herbicide and fungicide. Estaprop (dichlorprop/2,4-D), Buctril M (MCPA/bromoxynil), and Infinity (pyrasulfatole/bromoxynil) herbicides were applied singly and in combination with four fungicides and applications were made following a frost (night-time forecast of 0ºC) and at a late growth stage (Zadoks 37-39). Visual injury ratings indicated herbicide-fungicide tank-mixtures of Estaprop+Folicur (tebuconazole), Buctril M+Folicur, and Buctril M+Quilt (azoxystrobin/propiconizole) consistently caused injury at frost (2-15%) and ‘late’ (8-30%) application timings. Despite the level of injury, wheat plants recovered and, in the majority of cases, yields were unaffected.  These results suggest that tank-mixtures containing the fungicide Folicur consistently injure winter wheat plants. In addition, herbicide-fungicide tank-mixes are more likely to injure winter wheat when applied at a late crop stage. These results contribute to profitable winter wheat production by identifying herbicide and herbicide-fungicide combinations that minimize crop injury and yield loss.




PREEMERGENCE ETHOFUMESATE INCREASES POSTEMERGENCE SPRAY RETENTION ON COMMON LAMBSQUARTERS. A. R. Kniss1, D. C. Odero*2; 1University of Wyoming, Laramie, WY, 2University of Florida, Belle Glade, FL (330)

ABSTRACT

Greenhouse experiments were conducted to determine whether sublethal rates of ethofumesate applied preemergence (PRE) increased postemergence (POST) spray retention on common lambsquarters. Ethofumesate was applied PRE at rates from 0 to 224 g/ha, followed by POST treatment with either water or glyphosate (at 840 g ae/ha) to which a red dye had been added. Plants were immediately washed and spray retention determined spectrophotometrically. POST spray retention was influenced by the interaction of PRE ethofumesate rate and POST spray material. Common lambsquarters retained more glyphosate compared to water, regardless of PRE ethofumesate rate. Increasing the rate of PRE ethofumesate increased the POST spray retention of both water and glyphosate. PRE application of ethofumesate increased POST spray retention of water by 114% and glyphosate by 18% compared to no ethofumesate treatment as determined by non-linear regression. Ethofumesate rates of less than 90 g/ha increased POST spray retention to 95% of the total observed response.




BAS762ACH FOR POSTEMERGENCE WEED CONTROL IN DRY BEANS. P. Jha*1, J. O. Garcia1, A. Anand2; 1Montana State University, Huntley, MT, 2Montana State University, Bozeman, MT (331)

ABSTRACT

An experiment was conducted in 2010 at the Southern Agricultural Research Center, Huntley, MT to evaluate crop tolerance and weed control efficacy of BAS 762ACH and to evaluate current weed management programs in dry beans.  BAS 762ACH is a new product from BASF containing active ingredients, bentazon and imazamox.  Dry edible beans (Pinto) were planted on May 17, 2010 at a seeding rate of 67 kg/ha in 61-cm row widths.  The experiment was conducted in a randomized complete block design with four replications.  Weeds present at the test site were buffalobur, wild buckwheat, common lambsquarters, wild prosomillet, common mallow, kochia, and redroot pigweed.  Crop tolerance and efficacy of BAS 762ACH applied postemergence (POST) was compared with two standard POST herbicides, imazamox (Raptor) and bentazon (Basagran), applied alone or in mixtures.  Bentazon rate was 0.84 kg ai/ha when applied alone and 0.56, 0.75, 0.84, or 0.98 kg ai/ha when applied as a tank-mix with imazamox (0.035 kg ai/ha).  BAS 762 ACH was applied at 0.945 kg ai/ha.  All POST treatments included 1.0% v/v COC and 2.0% v/v UAN and applications were made at the first trifoliate-leaf stage of dry beans.  In addition to the POST only program, preplant incorporated (PPI) or PPI followed by POST weed control program was also evaluated.  The PPI only treatment included dimethanamid (Outlook) at 0.84 kg ai/ha plus pendimethalin (Prowl H20) at 0.96 kg ai/ha, and the PPI followed by POST program included dimethanamid (0.84 kg ai/ha) plus pendimethalin (0.96 kg ai/ha) followed by bentazon (0.56 kg ai/ha) plus imazamox (0.035 kg ai/ha).  A non-treated check was included for comparison.  Percent crop injury and weed control was visually rated in a scale of 0 (no injury or no control) to 100 (plant death or complete control) at 7, 14, 28, and 42 days after application (DAA) of POST herbicides.  Dry bean yields were recorded at harvest.  None of the herbicides caused significant injury (0 to 5%) to dry beans.  Bentazon applied alone did not provide any control of buffalobur.  Buffalobur control 42 DAA with BAS 762ACH was 94%, which did not differ from imazamox alone or imazamox plus bentazon (0.56 to 0.98 kg ai/ha) POST.  Wild buckwheat control 42 DAA with BAS 762ACH was 95%, and did not differ from other treatments, except imazamox applied alone.  Imazamox alone was weak on lambsquarters (48% control 42 DAA) and at least 0.75 kg ai/ha of bentazon was needed to achieve adequate control.  All treatments provided 100% control of common mallow, except imazamox applied alone.  Redroot pigweed control 42 DAA with BAS 762ACH was 100% and did not differ from other treatments.  Kochia control with imazamox alone was 64% and bentazon (≥0.56 kg ai/ha) was needed to obtain >95% control.  Bentazon alone failed to provide any control of wild prosomillet.  Pendimethalin and dimethanamid applied PPI provided >90% control of all weeds even in the absence of a follow-up POST herbicide application.  Dry bean yield with BAS 762ACH was 2002 kg/ha, which did not differ from any of the tank-mix combinations and averaged 44% higher than the imazamox or bentazon alone treatment.  In conclusion, BAS 762 ACH (0.945 kg ai/ha) provided crop safety and weed control comparable to bentazon (0.75 kg ai/ha) plus imazamox (0.035 kg ai/ha) applied POST in dry beans.




IMPACT OF TIME OF DAY ON HERBICIDE EFFICACY IN SOYBEAN. P. H. Sikkema*1, R. E. Nurse2, N. Soltani1; 1University of Guelph, Ridgetown, ON, 2Agriculture and Agri-Food Canada, Harrow, ON (332)

ABSTRACT

Field trials were conducted from 2008 to 2010 at two locations in southwestern Ontario (Harrow and Ridgetown) to investigate how the timing of herbicide applications throughout the day affects weed control in soybean.  Weed control following the application of six postemergence herbicides (bentazon, chlorimuron-ethyl, fomesafen, glyphosate, imazethapyr, and quizalofop-p-ethyl) at 600, 900, 1200, 1500, 1800, 2100 and 2400 hours was assessed. The control of velvetleaf and common ragweed was reduced when glyphosate was applied at 600, 2100, 2400 hours at Ridgetown but was not affected at Harrow. The control of redroot pigweed was reduced when glyphosate was applied at 2400 hours. Common lambsquarters and barnyardgrass were not affected by time of glyphosate application. The control of velvetleaf was reduced when imazethapyr was applied at 600, 2100, 2400 hours. The control of common ragweed was reduced when imazethapyr was applied at 2400 hours at Harrow but was not affected at Ridgetown. Control of redroot pigweed, common lambsquarters, and barnyardgrass with imazethapyr was not affected by application timing during the day. The control of velvetleaf was reduced with chlorimuron-ethyl only when applied at 2400 hours. Control of redroot pigweed, common ragweed and common lambsquarters was not influenced by application timing during the day with chlorimuron-ethyl. Efficacy of bentazon, fomesafen, and quizalofop-p-ethyl was not affected by time of application during the day. There was no effect of time of application on soybean biomass, seed moisture content, and seed yield for the herbicides evaluated. Based on these results, velvetleaf was the most sensitive to the time of day effect, followed by common ragweed, and redroot pigweed. Control of common lambsquarters and barnyardgrass were not influenced by time of application with the herbicides evaluated.




EFFICACY AND CROP TOLERANCE OF GF-2654 AND GF-2726 IN CORN. E. F. Scherder*1, M. E. Schultz2, A. T. Ellis3, J. S. Richburg4, J. A. Huff5, B. D. Olson6, G. R. Tofoli7; 1Dow AgroSciences, Huxley, IA, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, Greenville, MS, 4Dow AgroSciences, Headland, AL, 5Dow AgroSciences, Herrin, IL, 6Dow AgroSciences, Geneva, NY, 7Dow AgroSciences, Goiania, Brazil (333)

ABSTRACT

Efficacy and crop tolerance of GF-2654 and GF-2726 in corn. Eric F. Scherder, Marvin E. Schultz, Andrew T. Ellis, Neil A. Spomer, Ronda L. Hamm, John S. Richburg, Jonathan A. Huff, Brian D. Olson, Gustavo R. Tofoli, Dow AgroSciences, Indianapolis, IN.

 

Dow AgroSciences is developing and registering a new family of trait technologies for corn, soybean and cotton that will enable safe in-season use of 2,4-D in these crops. Use rates and application timings that the DHT product concept will enable were previously impractical due to crop injury concerns with 2,4-D in these crops. In 2010, GF-2654 and GF-2726, new and novel proprietary 2,4-D formulations, were evaluated in trials in the Mid-South and Mid-West to assess overall crop tolerance in DHT corn. Weed control efficacy on key problematic and hard to control weeds was also evaluated. 

 

The GF-2654 and GF-2726 formulations were evaluated in crop tolerance trials at rates ranging from 1120 g ae/ha to 4480 g ae/ha. No significant differences in overall DHT crop response were observed at 3, 7 or 14 days after application, when compared to the untreated checks. DHT corn demonstrated robust tolerance to these two new formulations, with overall crop response similar to the current amine formulation which is widely used in the marketplace today.

 

Weed control was also evaluated to determine if these new formulations provide control equal to 2,4-D amine products used in the marketplace today. Results from these trials showed that weed control with GF-2654 and GF-2726 was equal to current 2,4-D concepts, when compared at equal ratesEFScherder@dow.com




COLORADO LIGHT AVOIDANCE CORN ECOLOGY STUDY. P. Westra*1, C. J. Swanton2, E. Page2, M. Loux3, A. Dobbels3, K. L. Smith4, J. Bullington4, H. Wright5, C. L. Foresman6; 1Colorado State University, Fort Collins, CO, 2University of Guelph, Guelph, ON, 3The Ohio State University, Columbus, OH, 4University of Arkansas, Monticello, Monticello, AR, 5Syngenta Crop Protection Canada Inc, Guelph, ON, 6Syngenta, Greensboro, NC (334)

ABSTRACT

A detailed corn/weed ecology field study was conducted in sprinkler irrigated corn in 2009 and 2010 as a part of a suite of such studies carried out in Colorado, Ontario, Ohio, and Arkansas.  Winter wheat was planted the same day as the corn to ensure that emerging corn plants were surrounded by green non-corn neighbors.  The wheat emerged before the corn in both years, and with time the natural weed community of plants such as kochia, common lambsquarter, redroot pigweed, jimpson weed, barnyard grass, wild proso millet, and green foxtail dominated the non-corn plant complex.  A set of weed removal treatments included lumax applied preemerge, glyphosate applied post emerge at the 1, 3, 5, and 10 leaf stage of corn, and an untreated check plot.  Each year the study consisted of 6 replications with 20 corn plants permanently marked in the center 2 rows of plots 4 rows wide by 30’ in length.  Repeated measurements were taken on these 720 plants from emergence through hand harvest of each plant.  Results show that corn plants respond to the presence of weeds as early as the 1 leaf stage, and that the level of this response increases with the length of weed competition.  Common measurable responses include reduced corn height, a lag in leaf development, and a lag in the time to silking and tassel development.  More importantly, with increased time of weed competition, the variability in response of individual corn plants begins to rise rapidly, leading to greater scatter of the corn yield per plant, corn kernel number, and the overall stability of grain yield.  Season-long weed control caused 50% and 74% yield loss respectively in 2009 and 2010.  These results suggest that one of the best ways to protect the grain yield of elite corn hybrids is to ensure that weed control be based on very early season herbicide use including pre emerge chemistry if possible.




MAIZE ( /ZEA MAYS/ L.) FITNESS IN RESPONSE TO LIGHT QUALITY AND DROUGHT STRESS. W. Obeidat*, C. J. Swanton; University of Guelph, Guelph, ON (335)

ABSTRACT

Weed competition in maize (Zea mays) is influenced by light quality low red-far (R: FR) light ratio signal, reflected from the leaf surface of weeds. Research has shown that light quality signalling can delay the rate of leaf appearance (RLA), reduce biomass and alter root structure. If root structure is altered, then the plants ability to withstand abiotic stresses may be compromised. To test for this possibility, we hypothesized that the presence of early season weeds will alter maize root structure and thereby reduce the ability of maize to recover from drought stress.  Field studies were conducted under controlled fertigation for two growing seasons (2009, 2010) at Arkell Research Station, University of Guelph, Guelph, ON, Canada. A University of Guelph maize hybrid (CG108×CG102) was selected for the experiment and turfgrass was used as a surrogate weed. The experiment was designed such that no direct above or below ground competition occurred between the maize seedling and the turfgrass. The turfgrass was present from emergence of the maize seedling until the 6th leaf tip stage of maize development. At this leaf stage, the turfgrass was removed and drought stress was applied until severe leaf rolling symptoms occurred approximately 14 to 21 days after initiation of the drought stress in 2010 and 2009 respectively. Water was then returned to the system and continued until the maize plants reached maturity. Maize seedlings exposed to the low R:FR light signal reflected from the turfgrass until the 6th leaf tip stage displayed an initial increase in plant height and a reduction in the root-to-shoot ratio, stem diameter and root biomass. At maturity, preliminary results from 2009 suggest that the yield potential of maize with altered root systems caused by the R:FR ratio was reduced and that the addition of water stress further enhanced this loss in yield potential.




SIDEDRESS NITROGEN APPLICATION RATE AND COMMON LAMBQUARTERS EFFECT ON CORN GRAIN YIELD. L. E. Bast*, W. J. Everman, D. D. Warncke; Michigan State University, East Lansing, MI (336)

ABSTRACT

Early postemergence herbicide applications may result in weed re-infestations from late- emerging species, which compete with corn for soil nitrogen.  A field study was conducted in irrigated corn (Zea mays) at the Montcalm Research Farm near Entrican, MI in 2009 and 2010 to examine the effect of sidedress nitrogen application rate and the presence of common lambsquarters (Chenopodium album) on corn grain yield.  A randomized complete block design was used.  Factors included the presence or absence of common lambsquarters and 5 sidedress nitrogen application rates of 0, 56, 112, 168, and 224 kg N ha-1.  At planting, 78 kg N ha-1 was applied to all treatments.  At the V6/V7 corn growth stage, weed re-infestation was simulated by transplanting common lambsquarters (2-5 cm height) into corn rows at 5 plants m-1 and nitrogen fertilizer was applied.  Weed density was maintained throughout the growing season.  Corn and weed chlorophyll measurements were recorded at corn silking.  Above-ground common lambsquarters biomass was collected from two 1.5 m sections, fresh and dry weights recorded, and analyzed for total nitrogen content.  Grain yield was determined at harvest.  In 2009, chlorophyll content of corn and common lambsquarters increased with sidedress nitrogen application rate.  Common lambsquarters biomass was greatest when 168 and 224 kg N ha-1 was applied and contained the highest percentage of nitrogen when 112-224 kg N ha-1 was applied.  The presence of common lambsquarters and sidedress nitrogen rate both influenced grain yield, but there was no significant interaction.  Grain yield decreased by 251 kg ha-1 when common lambsquarters were present in the corn rows.  Grain yield increased when 0 to 56 kg N ha-1 was applied.  There was no difference in grain yield when 56-224 kg N ha-1 was applied.  In 2010, there was no difference in nitrogen assimilation by common lambsquarters and grain yield was not impacted by the presence of common lambsquarters.  Grain yield was greatest when 168 kg N ha-1 was applied.  Our 2009 results indicate that the presence of later-emerging common lambsquarters may reduce corn grain yields; however, these effects were not mitigated with sidedress nitrogen applications.  In 2010, weather conditions were more favorable for corn growth development than in 2009.  Common lambsquarters had no impact on yield in 2010, indicating that the crop may have been able to out-compete weeds better than in 2009.



THE EFFECT OF THE R:FR RATIO ON MAIZE ROOT MORPHOLOGY. M. Afifi*, C. J. Swanton; University of Guelph, Guelph, ON (337)

ABSTRACT

The red to far-red ratio (R/FR) is a light quality signal that has been shown to alter plant growth under non-resource limiting conditions. In a previous study we confirmed that the low R/FR ratio reflected from the stem and leaf surface of weeds reduced total root volume and root biomass in maize. In addition, by the fourth leaf tip stage of maize development, roots originating from seed versus stem tissue differed in their response to the R/FR ratio.  In order to provide a more mechanistic understanding of this change, we tested the hypothesis that the rate of root development up to an including the 4th leaf tip stage of maize would be reduced by the above ground reduction of the R/FR ratio. Laboratory experiments were conducted under non-resource limiting conditions using perennial ryegrass as the model weed species. In addition, the effect of the R:FR ratio on the root system of maize was tested using a non-biological far red refelectant. Under non-resource limiting conditions, the above-ground R/FR ratio reflected from the stem and leaf surface of perennial ryegrass delayed the emergence of the root radicle and initially reduced the mean relative growth rate of the entire root system from emergence until the fourth leaf tip. By the fourth leaf tip stage of maize, however, no differences in length was observed for either the radicle or seminal roots. Under weedy conditions, a delay in crown root emergence contributed to a reduction in root length. By the fourth leaf tip stage of maize, crown root length, diameter, surface area, and number were all reduced compared to crown roots grown under weed-free conditions. These results were confirmed using the non-biological Far Red reflectant. These changes in rate of root development will influence the ability of a plant to explore for limited resources and may reduce the ability of maize to respond to environmental stress. 




TEACHING UNDERGRADUATE WEED SCIENCE AS A. P. B. Trewatha*; Missouri State University, Springfield, MO (338)

ABSTRACT

The weed science course at Missouri State University has been taught as a traditional 3 days/week, 2 hour lecture, 2 hour lab course for many years. In fall 2010, the course was offered only as a “blended” course, meeting one day/week for the 2 hour lab, with lectures, written assignments and discussions provided online through Blackboard 8. At the end of the semester, students were surveyed on their preferences for this format and suggestions for improvement. The class was evenly split in preference for the blended format vs. the traditional format. Three-fourths of the class felt that having at least one additional face-to-face meeting would be the best option, perhaps because over 2/3 felt there was confusion on what was to be done online vs. in lab.  Respondents felt going to the field in lab, reviewing weed identification in lab, and making weed collections were the most favorite or useful aspects of the class. Online discussions, worksheets and having to get lecture material online were selected as the least favorite or useful. From both instructor and student perspective, it appeared having fewer written assignments (currently 1-2 per week) and having assignments always due on the same day of the week would be better. From the instructor’s view, teaching a blended course is a bit more challenging than a traditional or all online course, but the blended course may provide a more flexible format for students that can still provide the benefits of hands-on activities in lab. Additional information relating to online lecture format will be included in the presentation.




FORMING UNDERGRADUATE RESEARCH PARTNERSHIPS FOCUSED ON INVASIVE PLANTS. R. E. Loeb*; The Pennsylvania State University, DuBois, PA (339)

ABSTRACT




STATUS OF WEED SCIENCE AT LAND-GRANT UNIVERSITIES IN THE UNITED STATES AND ITS TERRITORIES. J. Derr*, A. Rana; Virginia Tech, Virginia Beach, VA (340)

ABSTRACT

Weeds are one of the main limiting factors in crop production, causing billions of dollars in annual global losses. Weeds also reduce access to land and water, impair aesthetics, and disrupt human activities and well-being.  Herbicides comprise approximately 68% of pesticide use, greater than insecticides and fungicides combined, documenting the significant impact of weeds.  To determine resource allocation in pest management, the number of faculty positions and undergraduate and graduate courses  devoted to weed science at all of the 72 land-grant institutions across the United States and its territories was determined and compared with that for plant pathology and entomology in a 2009 survey. When totaled across the 72 land-grant institutions, there are more than four times as many entomologists and more than three times as many plant pathologists as weed scientists. On average, each land-grant institution has 0.5, 1.4, and 1.1 full time equivalents (FTEs) devoted to weed science teaching, research, and extension, respectively.  However, the average land grant institution has 12.5 and 9.5 FTEs devoted to entomology and plant pathology, respectively.  There are approximately five times as many graduate students currently in entomology and almost three times as many in plant pathology compared with weed science. There are approximately five times as many entomology and two and a half times as many plant pathology undergraduate classes compared with weed science classes. These differences increase when graduate courses are considered. Most land-grant universities have either none or few graduate classes in weed science. There are more than six times as many graduate entomology courses and more than five times as many plant pathology courses compared with weed science graduate classes. There are no departments devoted solely to weed science, whereas entomology and plant pathology departments are both common. Most universities have little to no faculty assigned to horticulture, aquatic, or forestry weed control. Number of faculty assigned to weed management in olericulture, turf, or noncrop areas, or to weed biology, weed ecology, weed genetics, or herbicide physiology are also limited.  When compared to a survey conducted in 2003, there has been a greater reduction in weed science faculty compared to entomology and plant pathology in the northeastern U.S.  Based on the impact of weeds on crop production, recreation, and human and animal health, the ratio of weed scientists to entomologists and plant pathologists at land-grant institutions should be closer to 1:1:1 instead of the current ratio of 1.0:4.4-3.3.  Additional university resources are needed if weed science research, teaching, and extension efforts are to meet the priority needs for weed management in the agricultural, natural resources, and urban ecosystems.




TEACHING SPRAY NOZZLE TIP SELECTION. R. N. Klein*; University of Nebraska-Lincoln, North Platte, NE (341)

ABSTRACT




UGA WEED SCIENCE SURVIVAL KIT. E. P. Prostko*; University of Georgia, Tifton, GA (342)

ABSTRACT

The Georgia Peanut Achievement Club (GPAC) is an educational program sponsored by the University of Georgia (UGA) and Syngenta.  It has been in existence since 1950.  The purpose of the GPAC program is to educate, recognize, and reward outstanding peanut producers in the state.  As part of this program, UGA peanut extension specialists are challenged to present information that would not typically be delivered at local county production meetings.  In response to this challenge, the UGA Weed Science Survival Kit was created in 2009.  The objective of the UGA Weed Science Survival Kit was to remind growers of the basic principles of weed science.  A PowerPoint slide presentation, available on-line at www.gaweed.com, was developed to address nine important topics including the following: weed identification; herbicide labels; sprayer calibration; pesticide safety; spray nozzle tips; water volume; tractor speed; time of application; and herbicide modes of action.  While the slide presentation was delivered, the growers received a small, physical reminder of the topic being discussed.  When discussing the nine topics, the following were provided: weed identification (Weeds of the South); herbicide labels (reading glasses); sprayer calibration (wallet size UGA calibration card); pesticide safety (safety glasses); spray nozzle tips (laminated nozzle guide); water volume (water bottle); tractor speed (stop watch); time of application (UGA Weed Stik i.e. a ruler); herbicide modes of action (list of all herbicides with family and mode of action).  All of these items were placed in a bag with a UGA logo to remind the growers of the source of information.  The UGA Weed Science Survival Kit was so successful that Syngenta requested that the same presentation be made at their 2010 Southern Crop Consultants Meeting which was attended by more than 200 consultants from the region.   



IMPROVED HERBICIDE-RESISTANCE MANAGEMENT THROUGH EDUCATION: IMPLEMENTATION OF WSSA TRAINING MODULES TO INCREASE AWARENESS OF HERBICIDE-RESISTANCE MANAGEMENT. J. M. Stachler*1, W. J. Everman2, L. Glasgow3, J. Schroeder4, D. R. Shaw5, J. K. Soteres6, F. J. Tardif7; 1North Dakota State University and University of Minnesota, Fargo, ND, 2Michigan State University, East Lansing, MI, 3Syngenta Crop Protection, Greensboro, NC, 4New Mexico State University, Las Cruces, NM, 5Mississippi State University, Mississippi State, MS, 6Monsanto Company, St. Louis, MO, 7University of Guelph, Guelph, ON (343)

ABSTRACT

Grower and agrichemical retailer herbicide resistance education and training and has been identified as a critical path in advancing the adoption of proactive best management programs to delay or mitigate the development of herbicide resistant weeds.  Universities, private sector companies, crop commodity groups, and other groups have all been active in developing and distributing training materials to growers and the agricultural community at large.  In February 2010, a proposal was made and accepted by the WSSA Herbicide Resistant Plants Committee (E12) and the special task force on Herbicide Resistance Education (S71) to form a team of public and private sector weed scientists (see list of authors) to review current web-based herbicide resistance training modules, with the intent to update and modify these modules as appropriate.  The broad goals of the effort are to: (1) provide the most up-to-date information on causes and best methods for managing resistance, (2) increase consistency of basic messages to growers and retailers, (3) demonstrate to the public a unified public and private sector message of a science-based approach to managing resistance, and (4) increase incorporation of herbicide resistance training into formal certification programs such as the Certified Crop Advisor program.  The team is developing five modules around the following questions: (1) Why is proactive resistance management important? (2) How do herbicides work and what is herbicide site-of-action? (3) What is herbicide resistance? (4) How do I identify resistance to herbicides? , and (5) How do I manage resistance?  In addition, the team, in cooperation with other weed scientists and agronomists, is developing a separate module to address the specific issue of the impact of resistance management practices on conservation tillage. Each of these modules will be developed in multiple formats (web-based training, PowerPoint slides, and videos).  The modules will be made available to all who wish to use them and will be maintained and freely distributed by the WSSA.  WSSA will also work with grower organizations and others to develop and distribute these materials.



RISK ASSESSMENT OF GLYPHOSATE RESISTANCE IN WESTERN CANADA. H. J. Beckie*1, K. N. Harker2, L. M. Hall3, F. A. Holm4, R. H. Gulden5; 1Agriculture and Agri-Food Canada, Saskatoon, SK, 2Agriculture and Agri-Food Canada, Lacombe, AB, 3University of Alberta, Edmonton, AB, 4University of Saskatchewan, Saskatoon, SK, 5University of Manitoba, Winnipeg, MB (344)

ABSTRACT

With increasing incidence of glyphosate-resistant weeds worldwide, greater farmer awareness of the importance of glyphosate stewardship and proactive glyphosate resistance management is needed. A web-based decision-support tool (http://www.weedtool.com) comprising 10 questions has been developed primarily for farmers in western Canada to assess the relative risk of selection for glyphosate-resistant weeds on a field-by-field basis. We describe the rationale for the questions and how a response to a particular question influences the risk rating. Practices with the greatest risk weighting in western Canadian cropping systems are lack of crop rotation diversity (growing mainly oilseeds) and a high frequency of glyphosate-resistant crops in the rotation. Three case scenarios are outlined – low, moderate, and high risk of glyphosate resistance evolution. Based on the overall risk rating, three best management practices are recommended to reduce the risk of glyphosate resistance in weeds.




PREPARING VINEYARD MANAGERS FOR 2,4-D TOLERANT CORN AND SOYBEAN. L. Jiang*, D. Doohan; The Ohio State University, Wooster, OH (345)

ABSTRACT

Corn, soybean and cotton with genetically-based tolerance to growth regulating herbicides will soon be licensed for commercial production in the United States. These herbicides have a legacy off-site movement and injurious effects on fruits and vegetables. We expect planting of these new genetically-modified crops to bring about large increases in the use of 2,4-D and dicamba herbicides. Both are considered to be volatile herbicides, an important factor that has contributed to off-site movement along with spray drift.  During 2010 the Ohio Grape Industries Committee provided funds to conduct a preliminary risk assessment, and to conduct an extension campaign amongst producers to create awareness of the pending increased use of these herbicides.  Risk assessments were conducted in the greenhouse using Concord, Cabernet franc and Chambourcin, representing three major groups of grape variety grown in the US, vinifera, American and the hybrid between them.  2,4-D and dicamba were applied to actively growing grape plants alone or in combination with glyphosate.  Herbicides were applied as over-the-top aqueous sprays at 1/30, 1/100 and 1/300 X rates of each herbicide. Dilute sprays were based upon recommended rates of glyphosate at 0.84 kg ha-1, 2,4-D at 0.84 kg ha-1 and dicamba at 0.56 kg ha-1.  Each Treatment had four replications and data consisted of visual evaluations of injury at 1, 2 and 3 weeks after treatment. All three grape varieties tested were very sensitive to both 2,4-D and dicamba with obvious injury to the shoot tip at 1/300 X rates of both herbicides. In contrast, glyphosate caused no notable injury at 1/00 X rate. However, 2,4-D and dicamba  resulted in distinct patterns of injury. 2,4-D caused young leaf stretch abnormally, whereas dicamba induced up-ward cupping to young leaves so extended that they could not expand. The addition of dilute quantities of glyphosate intended to exacerbate the crop plant response.  The extension campaign consisted of five workshops conducted during June, July and August in different parts of the state.  Workshop activities included a presentation of results from the greenhouse trials, a demonstration and discussion of spray drift, and the influence of wind speed, pressure and nozzle type.  This was followed by a question and answer period made more enjoyable by wine-tasting.  The importance of developing and maintaining excellent communications with neighboring farms was emphasized.  A total of 109 Ohioans participated in these programs.




DEVELOPMENT OF THE UNIVERSITY OF ALASKA FAIRBANKS INVASIVE PLANT MANAGEMENT PLAN. M. E. Heidemann*1, S. Todd1, S. S. Seefeldt2, T. Wurtz3; 1University of Alaska Fairbanks, Fairbanks, AK, 2USDA-ARS, Fairbanks, AK, 3US Forest Service, Fairbanks, AK (346)

ABSTRACT

The University of Alaska Fairbanks Campus has a variety of invasive plants, many of which were introduced by UAF researchers and landscaping professionals. The impacts of invasive plants to the UAF campus extend beyond landscaping to recreational users, reindeer and other research animal health, research activities, and aesthetics. Several individuals began to recognize the need for committed invasive plant management on the UAF Campus. In 2009 the U.S. Forest Service Forest Health and Protection and UAF School of Natural Resources provided funding for the development of the UAF Campus Invasive Plant Management Plan. The plan was developed through a task-force process with 13 representative members of campus. An initial scoping process included interviews with task force members and other interested individuals to identify issues the plan should address. Task force members attended meetings from February through May 2010 to discuss these issues and make recommendations for invasive plant management on the UAF Campus. A public meeting was held to present a draft of the plan and gather public input. The final draft of the plan was written based on the agreements the task force developed in their meetings. It is currently being considered for acceptance as an addendum to the Campus Landscape Plan. The primary goals of the plan include focusing on best management practices, education and awareness, and management of existing infestations. The UAF Campus Invasive Plant Management Plan provides campus land managers with clear guidelines and management priorities to reduce current invasive plant infestations and prevent the establishment of new invasive plants.




WEEDIMAGES.ORG: AN EASY WAY TO SHARE IMAGES, MAPS AND INFORMATION. J. H. LaForest*1, T. M. Webster2; 1University of Georgia, Tifton, GA, 2USDA-ARS, Tifton, GA (347)

ABSTRACT

The Weed Science Society of America has partnered with the Bugwood Image Database to create WeedImages.org.  The images available on the site are freely available for non-commercial, educational use as long as the images are properly cited.  The website also includes distribution information as aggregated in EDDMapS, maps highlighting the most troublesome and most common weeds according to the Southern States Weed Survey, and a listing of what organizations consider a particular weed to be invasive.  In the coming year we will be looking for additional collaborators to expand of the most troublesome and most common weed lists, improve of the distribution information for weed species, and  improve the collection of images to illustrate more weeds on the WSSA weed list, herbicide symptoms and weed management practices.  




ANOVA UNDER DIFFERENT APPROACHES OF EXPRESSING TREATMENT MEANS AS A PERCENTAGE OF CONTROL MEAN. R. K. Godara*1, J. P. Geaghan2, B. J. Williams1; 1LSU AgCenter, Baton Rouge, LA, 2Louisiana State University, Baton Rouge, LA (348)

ABSTRACT

The absolute value of response variables like crop yield in many agronomic field experiments is not of much significance because these variables vary from experiment to experiment, which are conducted over different locations and years.  In these cases, the response of a treatment relative to control can be more useful. The recorded response for each treatment can be expressed as a percentage of control. There are three possible approaches to this technique viz. 1) perform ANOVA on the original data and then converting treatment MEANS or LSMEANS to a percentage of control for presentation purpose; 2) convert the recorded responses as a percentage of control for each of the replications before subjecting data to ANOVA; 3) convert the recorded responses as a percentage of mean response for control (mean of the replications) before subjecting data to ANOVA. Thus our objective was to determine and discuss the statistical validity of the three approaches mentioned above and to determine the best approach for analysis, inference and presentation of such data. Monte Carlo simulations were used to genetate several data sets and ANOVA were performed using mixed procedure of SAS.

Taking into consideration the fulfillment of the assumptions of the ANOVA,  statistical efficiency and power, and fulfillment of the objective of setting the control mean to 100, it was concluded that the best approach would be the first approach where ANOVA is performed on the on the original data and then treatment MEANS or LSMEANS are converted to percentage of control for presentation purpose.




UPDATED REPORT ON GENE FLOW. P. Byrne, P. Westra, C. T. Beil*; Colorado State University, Fort Collins, CO (349)

ABSTRACT

Abstract

Transgenic crops have been approved and have seen commercial success in some markets while in other markets they remain in the development stage, not yet approved. As transgenic crops begin to lift the constraints of environmental factors on crop production in the western U.S., crop developers will request deregulation of wheat (Triticum aestivum L.) lines with transgenes in the near future.

Successful release of transgenic crops in regions with related wild species involves careful monitoring, understanding, and risk assessment of gene flow. The long term goals of these series of studies are to develop the capability to predict the frequency and impact of introgression of transgenes from wheat to jointed goatgrass (Aegilops cylindrica Host.).   Estimates of landscape-level gene flow from wheat to jointed goatgrass in the Central Great Plains took advantage of imazamox-resistant ‘Above’ wheat to estimate field level hybridization. Rates of subsequent backcrossing of the hybrids to jointed goatgrass were also estimated in field studies. 

Because jointed goatgrass lacks the A and B genome, it has been suggested that the risk of gene flow from transgenic wheat to jointed goatgrass can be reduced by inserting transgenes into wheat chromosomes of these two genomes. However, there are several mechanisms for A and B genome chromosomes to become stably introgressed into jointed goatgrass.

The future of this project lies in identifying genome-specific sequence polymorphisms in order to track introgression of wheat sequences into jointed goatgrass. Combining this information with cytogenetic experiments will extend our understanding of the mechanisms of gene transfer from wheat to jointed goatgrass.




SHATTERCANE X SORGHUM OUTCROSSING IN THE FIELD. J. J. Schmidt*1, M. L. Bernards1, J. F. Pedersen2, J. L. Lindquist1; 1University of Nebraska-Lincoln, Lincoln, NE, 2USDA-ARS, University of Nebraska-Lincoln, Lincoln, NE (350)

ABSTRACT

Sorghum (Sorghum bicolor subsp. bicolor) can interbreed with its close weedy relative shattercane (S. bicolor subsp. drummondii).  The introduction of traits from sorghum into a shattercane population could contribute to the invasiveness of the wild shattercane population.  An in situ experiment was conducted across two years to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane.  Shattercane with juicy midrib (dd) was planted in a soybean field in concentric arcs at varying distances from a sorghum pollen source with dry midrib (DD). The arcs were placed so that prevailing winds would carry pollen from the sorghum to shattercane.  Shattercane panicles in anthesis during sorghum pollen shed were tagged and seeds were collected from those shattercane panicles. Progeny were evaluated using the dominant phenotypic marker to determine outcrossing rate.   Outcrossing differed between years but was greatest (3.6±0.76% in 2008 and 16.1±1.31% in 2009) for shattercane placed within the source and generally declined as distance increased for both years. In both years outcrossing was seen (0.09±0.04% in 2008 and 0.34 ±0.07% in 2009) at the farthest distance evaluated (200m). Results indicate that genes from sorghum and any associated traits could be introduced into shattercane populations at distances of at least 200 m and that outcrossing rate may be dependent on weather factors such as wind, and possibly pollen source strength.

 




THE EFFECT OF DIGESTIVE TRACT IN DIFFERENT HOLSTEIN CATTLE ON WEED SEED SURVIVAL. H. Rahimian Mashhadi*1, M. D. Banadaki2, S. Rahimi2; 1University of Tehran, Tehran, Iran, 2University of Tehran, Karaj, Iran (351)

ABSTRACT

The effect of digestive tract in different Holstein cattle on weed seed survival

Rahimian H. Mashhadi, Salman Rahimi*, Mehdi D. Banadaky

Department of Agronomy and Plant Breeding, and Department of Animal Science, Collage of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
 
A large number of weed seeds maintain their viability when passing through digestive tract of livestock. The objective of this study was to determine and compare the effect of digestive tract of four Holstein cattle groups (Lactating cows, Feedlot male calves, Dry cows and Growing heifers) on seed survival of four weed species (Cuscuta campestris Yuncker., Polygonum aviculare L., Rumex crispus L. and Sorghum halepense (L.) Pers). Four Cattle of each cattle groups were placed in individual stalls. Cattle were fed 1500 seeds of each species per Kg of their dry matter intake. Seed recovery (SR), seed viability (SV) and viable recovered seed (VRS) were measured in 1, 2, 3, and 4 days after seed intake. SR, SV, and VRS parameters were significantly different among different cattle groups. The highest rate of SR occured in the second day after seed intake in all cattle groups. No significant differences were observed in SR of weed species when their seeds were fed to dry cows. Dry and lactating cows had the lowest and highest rates of SR (36.5% and 74.8%; averaged over weed species) respectively. R. crispus had the lowest rates of SR in all cattle groups. At the first day after seed intake, SV values of all weed species except R. crispus was not affected by digestive tract of different cattle groups. Recovered seeds from feedlot male calves dung had the highest reduction in SV values among all cattle groups. Dry cows and growing heifers had similiar effects on reduction of SV values. The lowest and highest rates of VRS reduction were found in S.halepense in lactating cows and R.crispus in dry cows with 27% and 87.8%, respectively.

*Corresponding author’s E-mail: s.rahimi@live.com

 

 

 

 

 

 

 

 

 

 

 

 

 

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Cudney, D. W., S. D. Wright., T. A. Shultz. and J. S. Reints. 1992. Weed seed in dairy manure depends on collection site. Calif. Agric. 46(3): 31-32.

Dastgheibi, F. 1989. Relative importance of crop seed, manure and irrigation water as sources of weed infestation. Weed Res. 29: 113-116.

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IDENTIFICATION OF WEEDY SPECIES IN ALGAE PRODUCTION SYSTEMS. S. T. Chisholm*1, S. Fulbright1, J. Lang2, G. Wardle2, K. Dean2, P. Lammers2; 1Colorado State University, Fort Collins, CO, 2Solix Biofuels, Ft. Collins, CO (352)

ABSTRACT

Microalgae are a diverse set of photosynthetic prokaryotes and eukaryotes that use water, sunlight and carbon dioxide to produce biomass that includes oils appropriate for use as biodiesel. Algae-derived biodiesel is a promising alternative to petroleum-based transport fuels or plant feedstock-derived bioethanol and biodiesel. Different microalgae have unique oil compositions and growth characteristics; elite algae strains are selected for high oil content and other significant features, whereas undesired contaminants of the growth system (such as low-oil-content algae) are considered weedy species. In order to meet the transport fuel needs of a large population, even the most efficient oil-producing algae will have to be grown on a massive scale. It will be a significant challenge to maintain massive-volume aqueous monocultures of elite strains. Inevitable culture contamination by weedy species, predators or other pathogens will reduce the productivity and profitability of algae biodiesel production systems. To mitigate the impact of unwanted organisms, monitoring and management strategies must be developed. Toward this end, we are using molecular diagnostic tools to faithfully identify elite algae strains, weedy species, predators and pests. We developed molecular procedures to observe the level of culture contamination with weedy species and to specifically identify uncharacterized species contaminating the production system. Based on this growing catalog of weeds commonly found in growth systems, we are developing quantitative diagnostics for elite strains and previously identified weeds. These resources are an important first step toward developing culture management strategies to maximize system productivity.

 




ASPECTS OF FLORAL BIOLOGY AND POLLINATION ECOLOGY OF WHITE COCKLE (SILENE LATIFOLIA). J. F. Anderson*; University of Saskatchewan, Saskatoon, SK (353)

ABSTRACT




JOINTED GOATGRASS (AEGILOPS CYLINDRICA), A SECONDARY PRODUCT OF WHEAT DOMESTICATION? E. Sanchez Olguin*, J. Leonard, O. Riera-Lizarazu, C. Mallory-Smith; Oregon State University, Corvallis, OR (354)

ABSTRACT

Jointed goatgrass (Aegilops cylindrica) is a successful weed in winter wheat production. Ae. cylindrica has the genome composition CCDD. It probably arose by spontaneous hybridization between the CC genome species Ae. markgrafii and the DD genome species Ae. tauschii ssp. tauschii in the Fertile Crescent in Southwest Asia. Hexaploid wheat originated by hybridization between T. turgidum and A. tauschii ssp. strangulata in this same region about 10,000 years ago. Low levels of genetic diversity have been reported for Ae. cylindrica, suggesting that it is a relatively young species. Partial sequences from four nuclear genes, one chloroplast gene and four chloroplast intergenic regions were used to study the evolutionary history of Ae. cylindrica and estimate the timeline for its polyploidization. High levels of similarity between Ae. cylindrica and its parental species were observed in nuclear and chloroplast coding and non-coding sequences. A total of 3389 sites from the intergenic regions of the chloroplast were evaluated. The number of polymorphic sites per intergenic region varied from zero to seven. The Tajima D is a selection test to distinguish between a DNA sequence evolving under the neutrality theory and one evolving under selection, demographic expansion or contraction, or introgression. In the case of Ae. cylindrica, values ranged from -0.933 to -1.77. Negative values for this statistic are associated with purifying selection or populations that are in expansion. A total of 2639 base pairs corresponding to the intron regions from four nuclear genes were used for a phylogenetic analysis to determine the relationships among the taxas. Phylogenetic analysis clearly separated the C genome from the D genome. Within the D genome, two clades were observed. One clade included Ae. tauschii ssp. tauschii and all the sequences of the Ae. cylindrica D genome. The other clade included Ae. tauschii ssp. strangulata and the D sequence of wheat. The estimated divergence time between the genomes from the parental species and Ae. cylindrica suggested that Ae. cylindrica is a young species close in age to hexaploid wheat and may have arisen as a byproduct of wheat’s domestication. The results of this study provide a better understanding of the origin and evolution of this weedy species.




ROLE OF BENZOXAZINOID COMPOUNDS IN RYE ALLELOPATHY IN SOIL. J. R. Teasdale*, C. P. Rice, G. Cai; USDA-ARS, Beltsville, MD (355)

ABSTRACT

The activity of allelopathic compounds is often reduced in the soil environment where processes involving release from donor plant material, soil adsorption and degradation, and uptake by receptor plants interact according to complex kinetics.  Rye cover crops are known to suppress weeds in agronomic environments and to produce benzoxazinoid (Bx) compounds which are phytotoxic in laboratory assays.  Experiments were conducted to determine Bx soil concentrations and suppression of lettuce (Lactuca sativa L.) and smooth pigweed (Amaranthus hybridus L.) indicator plants in soil assays after field incorporation of rye residues.  Maximum total soil concentrations of all Bx compounds ranged from 27 to 136 ng g-1 across sites and years.  The dominant Bx species were the non-toxic lactams, HBOA and HMBOA, and the moderately toxic benzoxazolinones, BOA and MBOA, which combined to make up 69 to 81% of the total.  However, the more toxic benzoxazinones, DIBOA and DIMBOA, and the highly toxic phenoxazinone, APO, were present in negligible amounts.  Suppression of lettuce and smooth pigweed persisted for approximately two weeks after rye incorporation, which corresponded to the period when elevated levels of Bx compounds were detected in soil, suggesting the potential for allelopathic involvement.  The most abundant Bx species found in these soils with known phytotoxic properties, BOA and MBOA, were exogenously added to soils to maintain continuous daily extracted levels up to 8 µg g-1 soil (50 to 300 times higher than total extracted Bx compounds measured in field soils), but no significant inhibition was observed on smooth pigweed assay plants.  The majority of exogenously supplemented Bx compounds persisted for less than 24 hr in soil and diffused less than 1 cm from the point of application.  These results suggest that seeds germinating and growing in field soil would be embedded within steep spatial gradients of Bx compounds released from decomposing root and shoot fragments as well as temporal gradients determined by release and degradation cycles.  Consequently, it is possible that local spatio-temporal windows with high Bx concentrations within the soil environment may exist that could account for inhibition of selected plants germinating and growing within in these windows of Bx availability.  Whether there were a sufficient number of these Bx windows with phytotoxic soil solution concentrations to account for the relatively high levels of suppression observed in these assays is doubtful.  Results suggest that the associations between indicator plant suppression and rye Bx concentrations were probably not causal, and other compounds released with a similar dynamics as Bx were likely responsible.




MODELLING HERBICIDE EFFECTS ON RICE-WEED COMPETITION IN TRANSPLANTED RICE CULTIVATION. D. Kim1, B. Moon*2, J. Kim1; 1Seoul National University, Seoul, South Korea, 2Rural Development Administration, Suwon, South Korea (356)

ABSTRACT

The effects of herbicide dose on rice-weed competition were investigated by using the data from the rice field studies with two major paddy weeds, Echinochloa crus-galli and Eleocharis kuroguwai, in 2007 and 2008 and the combined model developed by Kim et al. (2002). Weed competitivities of E. crus-galli and E. kuroguwai were decreased with increasing flucetosulfuron and azimsulfuron doses in the same manner as the standard dose-response curve, respectively. The combined model of rectangular hyperbolic model and the standard dose-response curve described well the complex effects of herbicide dose and weed competitivity on rice yield. The model and parameter estimates were used to predict rice yield and estimate the flucetosulfuron and azimsulfuron doses required to restrict rice yield loss caused by Echinochloa crus-galli and Eleocharis kuroguwai, respectively, to an acceptable level. The model was then further modified to estimate the herbicide doses to achieve a target rice yield. For the rice yield of 5.0 t ha-1 with infestation of 12, 24, and 48 E. crus-galli plants m-2, the model recommended flucetosulfuron doses of 8.7, 13.4, and 20.1 g a.i. ha-1, respectively. For the rice yield of 5.2 t ha-1 with infestation of 24, 48, and 96 E. kuroguwai plants m-2, the model recommended azimsulfuron herbicide dose of 3.9, 7.5, and 12.6 g a.i. ha-1, respectively.



MULCHING COVER CROP MIXTURES FOR IMPROVED WEED SUPPRESSION IN ORGANIC GRAIN CROPS. S. E. Wortman*, J. L. Lindquist, M. L. Bernards, R. Drijber, C. Francis; University of Nebraska-Lincoln, Lincoln, NE (357)

ABSTRACT

Many studies have demonstrated the weed suppressive potential and fertility contributions of individual cover crop species, but the value of diverse cover crop mixtures has received less attention. Moreover, there is increasing interest in conservation tillage strategies for cover crop termination. The objective of this study was to determine the effects of cover crop diversity and termination method on weed suppression, soil nitrogen availability, soil water content and grain yield in an organic cropping system. A field experiment was conducted in 2009 and 2010 near Mead, NE where spring-sown mixtures of 2, 4, 6 and 8 cover crop species were included in a sunflower – soybean – corn crop rotation. Cover crops were planted in late-March, terminated in late-May using a field disk or undercutter and main crops were planted within one week. Cover crop termination with an undercutter only decreased weed biomass by 4% (±2.5%) relative to the no cover control at 34 days after planting main crop (DAP) in 2009.  However, the combined effects of increasing cover crop diversity and termination with an undercutter increased weed suppression at 23 DAP in 2010; weed biomass in the undercut 8 species mixture was reduced by 46% (±12.6%) relative to the no cover control. Undercutting cover crops increased soil nitrogen availability (3.2 ppm ± 0.2) relative to incorporation with a disk (2.2 ppm ± 0.2) at 29 DAP in 2010. All cover crop mixtures reduced soil water content prior to main crop planting, while cover crop termination with an undercutter increased soil water by as much as 7.3% (± 0.2%) compared to the field disk during early main crop growth. Most importantly, cover crop termination with an undercutter increased corn and soybean yields by as much as 32% (±7%) and 34% (±16%) compared to the no cover control, respectively.




EMERGENCE AND DEVELOPMENT OF RED SORREL (RUMEX ACETOSELLA L.) AND WILD BLUEBERRY RAMETS (VACCINIUM ANGUSTIFOLIUM AIT.). S. N. White*; University of Guelph, Truro, NS (358)

ABSTRACT




THE INTERACTION OF SHADE AVOIDANCE AND STRESS ON GROWTH DEVELOPMENT AND YIELD OF MAIZE. E. Page, W. Liu, D. Cerrudo, C. J. Swanton*; University of Guelph, Guelph, ON (359)

ABSTRACT

Previous studies have suggested that the reduction in the root/shoot ratio that accompanies the shade avoidance response may reduce the tolerance of individuals to subsequent nutrient or moisture limitations. In this work, we examined the impact of the shade avoidance response on maize seedling growth and development and the response of these plants to a subsequent abiotic stress. Seedlings were grown in a field fertigation system under two light quality environments: an ambient and a low red-to-far-red ratio environment, which were designed to simulate weed-free and weedy conditions, respectively. This system also enabled the controlled restriction of water and nutrients, which reduced the relative growth rate of the crop and created a secondary stress. Results of this study indicate that, while the shade avoidance response did reduce the root/shoot ratio in maize, this effect was not responsible for the reduction in tolerance to a subsequent stress. Rather, the apparent additivity or synergism of shade avoidance and the secondary stressor on yield loss depended on whether the net effect of these two stressors was sufficiently large to shift the population toward the point where reproductive allometry was broken.




A QUICK AND COLORFUL METHOD TO DETECT AND QUANTIFY SHIKIMIC ACID IN WHOLE PLANT TISSUES OR PLANT EXTRACTS. K. A. Kretzmer*1, D. Sammons2, J. P. Frantz1, P. J. Morris1; 1Monsanto Company, St Louis, MO, 2Monsanto Company, St. Louis, MO (360)

ABSTRACT

 

Plant tissues sensitive to glyphosate accumulate shikimic acid to high levels after glyphosate treatment. The detection of shikimic acid has been shown to be a useful marker as a measure of glyphosate injury or to score for glyphosate sensitive and resistant weed biotypes. Up to now, the most common methods for shikimic acid assay include HPLC with uv detection, and the periodate oxidation, or Cromartie and Polge, method. Here we show a new method for shikimic acid detection which has broad application, is sensitive, simple and very quick. The method can be used for quantification in plant extracts using a microtiter plate, and can be further adapted for detection of shikimic acid in intact leaf discs or other plant tissues, and in whole plants.




TEMPORAL AFFECTS ON THE GLYPHOSATE CHLORIMURON INTERACTION. R. K. Bethke*1, J. Michael2, D. Penner2; 1Auburn University, Auburn, AL, 2Michigan State University, East Lansing, MI (361)

ABSTRACT

Previous studies in the field and greenhouse have shown that there are antagonistic interactions between glyphosate and chlorimuron. The basis of these negative interactions is not fully understood and is the basis for this paper. Time of application, either early morning, midday, or late afternoon were used to determine the effect of time of day on herbicide efficacy. Glyphosate provided greater control of common lambsquarters when applied in the morning than at all the other times.  There was no difference in velvetleaf control with respect to time of day. Chlorimuron had greater control of velvetleaf with the mid-day application than at other application times.

Separate subsequent applications were used to determine the ideal interval between the fast-acting and slow-acting herbicides necessary to prevent an antagonistic interaction. Applications of glyphosate followed by chlorimuron at 2, 4, 6, 8, 24, 36, and 48 hours showed no difference in weed control from the two herbicides applied initially in combination. 




RESPONSE OF CONYZA SPP TO GLYPHOSATE IS TEMPERATURE AND PLANT AGE DEPENDENT. B. Rubin*, Z. Kleinman, G. Ben-Ami, M. Sibony; Hebrew University of Jerusalem, Rehovot, Israel (362)

ABSTRACT

Hairy fleabane (Conyza bonariensis), horseweed (C. canadensis) and rigid ryegrass (Lolium rigidum) are common weeds in various habitats in Israel including annual and perennial crops and roadsides. Glyphosate alone or in combination with other herbicides is widely and repeatedly used for total vegetation control and for chemical fallow. Two glyphosate-resistant (GR) and two glyphosate-sensitive (GS) hairy fleabane populations were investigated. Shikimate accumulation was determined in leaf discs floated in various concentrations of glyphosate for 18 h in the light (in vitro) and in leaf discs taken from glyphosate (0.18 kg ae ha-1) treated plants 0, 8, 24, 48, 120 and 240 HAT (in vivo). No differences were detected in shikimate accumulation between GR and GS C. bonariensis leaf discs in vitro treated with glyphosate, indicating similar sensitivity of EPSPS in GR and GS plants. However, 3 fold shikimate was accumulated in glyphosate-treated in the GS leaves as compared to GR leaves indicating that less glyphosate has reached the target site in GR plants as compared to GS plants. In addition, glyphosate applied on mature leaves only or on young leaves only resulted in much higher shikimate levels in sinks (roots and young leaves) of the GS plants as compared to GR plants, indicating rapid herbicide translocation to in these sinks. The finding supports our hypothesis that a sensitive EPSPS enzyme is present in GR biotypes and impaired translocation is the cause for low efficiency of glyphosate in these biotypes. Studies with 14C-glyphoste uptake and translocation and the fact that no differences were detected in the EPSP gene isolated from GR or GS plants further confirmed this hypothesis.



RESPONSE PATTERNS OF SUSPECTED GLYPHOSATE RESISTANT KOCHIA ACCESSIONS. A. Wiersma*1, P. Westra1, J. E. Leach1, C. Preston2; 1Colorado State University, Fort Collins, CO, 2University of Adelaide, Adelaide, Australia (363)

ABSTRACT

Glyphosate resistant kochia (Kochia scoparia) populations in Kansas, Nebraska, Colorado, North Dakota, and South Dakota pose a serious threat to sustainable crop production in the Central Great Plains. In 2010, at the CSU greenhouses, a large number of suspected glyphosate resistant kochia accessions (roughly 10,000 individual plants) were screened at .75 and 1.25 lbs/acre—yielding further indications of glyphosate tolerance across the plains states.  Phenotypic response patterns of glyphosate resistant kochia have been documented at the field and individual plant level.  At the field level, surviving plants were found in streak patterns, indicating that seed was likely dispersed from a single tumble weed dropping resistant seed across the landscape. At the individual plant level, chlorosis is followed by necrosis of leaf tips and meristem, and new growth develops from axillary buds. Several studies have been initiated to determine the mechanism of glyphosate resistance.  A study comparing plants grown in the greenhouse to those grown in pots outdoors suggests that growing conditions have an effect on the response of kochia to glyphosate. Absorption and translocation of 14C- labeled glyphosate revealed no difference between susceptible and resistant Kansas kochia accessions (Jason Waite, KSU).  Other potential mechanisms of resistance that are currently under investigation include 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene amplification and target site mutation. An effort to sequence the EPSPS gene exon containing the active site at Proline 106 is currently underway.  




GLYPHOSATE RESISTANCE IN CONYZA BONARIENSIS AND LOLIUM RIGIDUM IN ISRAEL. Z. Kleinman, M. Matzrafi, M. Sibony, B. Rubin*; Hebrew University of Jerusalem, Rehovot, Israel (364)

ABSTRACT

Hairy fleabane (Conyza bonariensis) and horseweed (C. canadensis) have become troublesome weeds in agriculture, mainly under minimum tillage, roadsides and perennial crops. In a nationwide survey conducted by our laboratory more than 100 Conyza spp. populations were collected in sites where glyphosate was applied and failed and tested for glyphosate resistance (GR). However, repeated tests in time and space resulted in a large variation in plant response to glyphosate, indicating strong effect of growth conditions (plant age, temperature and light intensity). Three biotypes of each Conyza spp. were grown in a greenhouse at 25/180C before transfer at the rosette stage (60 DAP) to four different temperature regimes: 16/100C; 22/160C; 28/220C and 34/280C (D/N). Three days later the plants were treated with various rates of glyphosate. Shoot fresh weight of treated plants was recorded at 21 DAT. The same populations were grown under 28/220C and treated with glyphosate (0.36 kg ae ha-1) at five different ages while the plants are at the rosette stage. Shoot fresh weight was determined 21 DAT. A significant linear correlation was found between temperature and plant response to glyphosate (ED50 values) of each biotype, so that plants grown under a high temperature regime were 2 to 10 fold more tolerant to glyphosate than plants grown under a low temperature regime. Similarly, a linear correlation of plant age with glyphosate damage was plotted indicating that the response of both Conyza species to glyphosate significantly decreases with plant age in spite of being at the rosette stage. In addition, we found that plants grown under low light intensity are significantly more sensitive to glyphosate than plants grown under full day light. These results clearly indicate that the response of both hairy fleabane and horseweed plants to glyphosate is highly dependent on environmental conditions. Several multiple resistant rigid ryegrass populations were identified in arable crops exposed to continuous selection pressure of glyphosate and ALS and ACCase inhibitors. Details on these populations will be described.




GLYPHOSATE RESISTANCE IN A JOHNSONGRASS (SORGHUM HALEPENSE L.) BIOTYPE FROM ARKANSAS. D. S. Riar*, J. K. Norsworthy, D. B. Johnson, R. C. Scott, M. V. Bagavathiannan; University of Arkansas, Fayetteville, AR (365)

ABSTRACT

Johnsongrass is one of the most troublesome weeds of the world and is listed as a noxious weed in Arkansas.  Reduced johnsongrass control with the recommended application rate of glyphosate was reported in a continuous soybean field near West Memphis, AR, in the fall of 2007.  A greenhouse study was conducted to (a) confirm and characterize glyphosate resistance in the johnsongrass biotype from West Memphis and (b) determine whether resistant and susceptible biotypes have differential glyphosate absorption or translocation.  Dose response studies revealed that the resistant biotype was 5- to 7-fold less sensitive to glyphosate than the susceptible biotype.  Glyphosate absorption was similar in resistant and susceptible biotypes at 72 h after treatment (HAT).  However, the treated leaf of the resistant biotype retained 28 percentage points more absorbed 14C-glyphosate compared to the susceptible biotype at 72 HAT.  Additionally, the resistant biotype had less 14C-glyphosate translocated to the aboveground tissue below the treated leaf and to roots compared to the susceptible biotype at 24 and 72 HAT.  Reduced translocation and increased retention of glyphosate in treated leaves is the probable mechanism of resistance in this glyphosate-resistant johnsongrass biotype.




SUMMARIZING GLYPHOSATE RESISTANCE MECHANISMS: MORE EXCLUSION EXAMPLES. D. Sammons*1, E. Ostrander2, B. Duncan2, X. Ge3, A. D'Avignon3, J. Ackerman3, K. L. Smith4, A. Collavo5, M. Sattin6; 1Monsanto Company, St. Louis, MO, 2Monsanto, St. Louis, MO, 3Washington University, St. Louis, MO, 4University of Arkansas, Monticello, Monticello, AR, 5Consiglio Nazionale delle Ricerche (CNR), Padua, Italy, 6CNR, Padua, Italy (366)

ABSTRACT


Classical mechanisms for weed resistance to herbicides are not the principal mechanisms for glyphosate resistance.  While target site mutations in EPSPS are known in several species, eg., Loliu and Eluesine,  they are fairly ineffectual accounting for only a small portion of the resistance magnitude.  Glyphosate metabolism is still rare and although now measured in a few species by Duke et al., none of the resistant species are noted as using metabolism.  Glyphosate resistant Conyza canadensis has now been shown to sequester glyphosate into the cell vacuole by 31P NMR and this sequestration mechanism also seems to operate in glyphosate resistant Lolium sp.  A number of weeds  have now been examined by 31P NMR and more novel observations of intracellular and extracellular glyphosate made.  These will be summarized and a discussion on various types of exclusions mechanisms put into the context of glyphosate resistance.



UNDERSTANDING THE MN CHELATION PROPERTIES OF GLYPHOSATE IN GLYPHOSATE-RESISTANT SOYBEAN. D. Sammons*1, S. Murdock2, M. Bleeke2, A. Mehrsheikh2, R. Grabiak2, W. Harris3; 1Monsanto Company, St. Louis, MO, 2Monsanto, St. Louis, MO, 3University of Missouri St. Louis, St. Louis, MO (367)

ABSTRACT

Glyphosate has long been characterized as a chelator of divalent cations and other multivalent cations found in plants, soil and water systems. Hard water has long been recognized as a source of Ca, and Mg ions as well as others less prevalent ions like Mn, Fe, Zn etc.  These ions have repeatedly been reported to form complexes with glyphosate and can in some hard water cases interfere with the herbicidal potency of the glyphosate applied to control weeds.  This basic physical ability to complex multivalent cations has lead to speculation that glyphosate could interfere with key metabolic processes and metal ion nutrition.  These effects in herbicide management matter not at all, but the postulate that the formation of metal ion complexes in glyphosate-resistant crops impacts the physiology and ultimately the yield of these crops has been widely solicited as a reason to apply micronutrients to all glyphosate-resistant crops.  The concentration of glyphosate in various parts of glyphosate-resistant soybean has been measured.  The theoretical modeling of competitive glyphosate metal ion complex formation has been calculated to show that glyphosate-Mn compex formation is well below the physiological nutrient range.  Further, field studies examining the effects of Mn nutrition on glyphosate-resistant soybeans shows that added Mn has no effect on overall yield.



EVIDENCE FOR MATERNAL INHERITANCE OF GLYPHOSATE RESISTANCE IN AMARANTHUS PALMERI. D. N. Ribeiro*1, F. E. Dayan2, P. Zhiqiang3, S. O. Duke3, D. R. Shaw4, V. K. Nandula5; 1Mississippi State University, Starkville, MS, 2USDA-ARS, University, MS, 3USDA-ARS, Oxford, MS, 4Mississippi State University, Mississippi State, MS, 5Mississippi State University, Stoneville, MS (368)

ABSTRACT

Glyphosate is considered by many as the most important herbicide ever developed. Repeated glyphosate applications causes selective genetic pressure toward evolution of resistant weeds. Glyphosate-resistant (R) Palmer amaranth populations (R1 and R2) were identified in Mississippi. The inheritance of glyphosate resistance was examined by reciprocally crossing R maternal parents with susceptible (S) paternal parents (R/S) and crossing S maternal parent with R paternal parents (S/R) to generate F1. Individuals from the F1 populations were submitted to glyphosate dose-response assays resulting in a range of phenotypes from R to S, with complete dependence on the direction of the cross. The response to glyphosate was more similar to the R than S parent when the female parent was R. Conversely, when R was used as pollinator the response to glyphosate was more similar to the S parent. Thus, glyphosate resistance appears to be a maternally inherited trait. Another explanation is that apomixis (parthenogenesis) may be occurring or there were differences in the transmission rate between male and female gametes. This led us to study the molecular basis of glyphosate resistance inheritance. Sequence comparisons of the predicted 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) mature protein from R1, R2, and S did not identify a target site mutation known to confer resistance in R populations. EPSPS activity was lower in S and S/R plants than in R and R/S plants in the absence of glyphosate; all were equally inhibited by the presence of glyphosate. Genomic estimation of EPSPS gene copy number relative to acetolactate synthase (ALS) using quantitative PCR showed that R and R/S contain more copies of EPSPS than S and S/R, supporting a maternal mode of inheritance of copy number. Western Blot analysis confirmed that increased EPSPS protein levels were correlated with EPSPS copy number. Quantitative RT-PCR on cDNA revealed that EPSPS was highly expressed in R1 and R/S, although poorly expressed in S, S/R, and R2. Consequently, elevated EPSPS copy number correlated with expression level and resistance in most studied populations, with the exception of R2. These results suggest that increased copy number alone does not automatically confer resistance to glyphosate. Therefore, another determinant is probably involved in resistance to glyphosate besides the increased EPSPS copy number. Such information may be useful in the development of management strategies for glyphosate resistance in weeds.



CHARACTERIZATION OF EPSPS GENE AMPLIFICATION IN PALMER AMARANTH (AMARANTHUS PALMERI). T. A. Gaines*1, S. Ward2, J. E. Leach2, S. T. Chisholm2, P. Westra2; 1University of Western Australia, Crawley, WA, Australia, 2Colorado State University, Fort Collins, CO (369)

ABSTRACT

Glyphosate functions by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).  Following widespread repeated glyphosate applications in glyphosate-resistant cropping areas, multiple glyphosate-resistant weeds have emerged.  We determined the resistance mechanism in a population of glyphosate-resistant Palmer amaranth from Georgia.  Within this population, glyphosate resistance correlates with increases in (a) genomic copy number of EPSPS, (b) expression of the EPSPS transcript, (c) EPSPS protein level and (d) EPSPS enzymatic activity.  Thus, it appears that amplification of the EPSPS gene produced an abundant supply of uninhibited EPSPS in the presence of glyphosate.  EPSPS gene amplification in Palmer amaranth raises questions related to how amplification initially occurred and was subsequently maintained, and what role this process has in evolution of Palmer amaranth as a troublesome weed with a history of independently developing resistance to different herbicides.  Inheritance studies indicate EPSPS gene copy number is unstable between generations, suggesting amplification (as well as reduction) of copy number is an ongoing, dynamic process.  Using fluorescent in-situ hybridization, we observed EPSPS loci on all chromosomes visible in a chromosome spread derived from a glyphosate-resistant Palmer amaranth plant.  The dynamic nature of the EPSPS copy number as well as the seemingly random insertion of EPSPS across Palmer amaranth chromosomes suggest amplification of this locus may be mediated by a mobile genetic element.