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.

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. 

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.

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.

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.  

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.

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.

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. 

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.

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.

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.

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’. 

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.

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).

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.  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

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.

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.

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.

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 wheat – 1) 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.

Pindar^TM 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

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

 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.

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.

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. 

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. 

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. 

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 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 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.

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.

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.

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. 

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’.

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.

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.

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. 

     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.

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. 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)

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.

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. 

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.

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.

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 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.

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.

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. 

 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

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.  

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 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.

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 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”.

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.

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?

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

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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.

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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.

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).

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 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.

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.

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 30^th, 2009 and September 16^th, 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.

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.

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.

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. 

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 T_base and Ψ_base 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.

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.

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.

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 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 (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

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.

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

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.

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.  

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.   

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

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.

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).

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 5^th unfolded leaf stage. The pathogen was re-isolated from lesions after 15 days. 

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.

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.

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.

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

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 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 (K_c) describes the amount of biomass produced per unit transpiration at a given vapor pressure deficit. K_c values of several crop species are known, but K_c 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 K_c values of field pennycress, common lambsquarters, pinnate tansymustard and dandelion and how K­_c­ 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. K_c 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 K_c values differed among the four weed species tested. K_c 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. K_c 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 K_c values for pinnate tansymustard or dandelion, but K_c values decreased between first bloom (vegetative growth) and seed maturity (complete life cycle) for field pennycress and common lambsquarters.  

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 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.

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.

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