Arrowweed (Pluchea sericea) is a C3, perennial woody shrub native to southwestern deserts that can grow up to 10 feet in height and is found in low-lying areas where water is intermittently available. It is particularly invasive in irrigation systems in central and western Arizona where it can destroy concrete-lined irrigation ditches. In earthen canals, arrowweed growth can greatly restrict water flow and tremendous costs are incurred by irrigation districts for mechanical control and restructuring of canals. Arrowweed has periods of active growth in the spring and early summer when it flowers and in the fall. It grows very slowly in the summer during the hottest months and in the winter. Two studies were conducted to test the efficacy of aminopyralid, triclopyr, glyphosate and dicamba on arrowweed in Sacaton, AZ (central Arizona) and near Posten, AZ (Parker Valley in western Arizona). In Sacaton, the herbicides were applied on October 12, 2007 using a backpack sprayer and a 10-ft, 6 nozzle boom with a carrier volume of 23 GPA. An organosilicone surfactant was used and plants along a concrete lined irrigation ditch were sprayed. Because of the size of the plants it was not possible to spray over the top of the arrowweed at Sacaton. In Posten, a utility vehicle with a spray system and boomless nozzle mounted 6 ft above the ground were used to apply the herbicides with a methylated seed oil in 18 or 21 GPA (depending on treatment) on December 5, 2008. Since the plants were a little smaller in Posten and the spray swath was 16 feet, plants closest to the vehicle were sprayed over-the-top. Herbicide symptoms developed slowly over several months; aminopyralid had little effect on arrowweed with the greatest efficacy achieved being 10% at 5 months after treatment (MAT). The best treatments were tryclopyr at 2 to 3 lb ae/a and glyphosate at 2.5 to 3.7 lb ae/A at 5 MAT at 70% control. Plants exhibited regrowth in early summer following fall-winter treatments suggesting that multiple or regular treatments will be required to suppress arrowweed and reduce irrigation system maintenance costs.

Switchgrass (Panicum virgatum L.), a perennial native grass, may be an alternative to corn for efficient biofuel production.  However, control of grassy weeds has been a problem in switchgrass production.  The objective of this research was to determine the efficacy of various herbicides for weed control in switchgrass.  A total of 23 post-emergent herbicides from 15 families were evaluated in a series of greenhouse trials.  The herbicides that did not injure switchgrass, but reduced smooth brome (Bromus inermis Leyss.) and quackgrass [Elymus repens L. (Gould)], were selected for field evaluation.  Field trials were conducted in an established switchgrass stand at the Central Grassland Research Extension Station near Streeter, ND.  Herbicides were applied at common and maximum use rates either on May 21 or June 25 in 2009, and grasses were harvested in August 2009 and 2010.  In 2009, quackgrass was reduced more than 90% by propoxycarbazone, sulfometuron, and sulfosulfuron when applied in May.  Smooth brome was reduced 100% with aminocyclopyrachlor, pyroxsulam, or sulfosulfuron.  However, switchgrass yields were similar to the control regardless of treatment.  Treatments applied in June were not effective.  One year after treatment with aminocyclopyrachlor and sulfometuron, switchgrass production increased by 2X to 3X, respectively, but smooth brome and quackgrass also rapidly reestablished.  Despite increased switchgrass yield, no herbicide provided satisfactory long-term weed control.

Early detection and rapid response (EDRR) to new species, as well as containment and/or reduction of established species are critical for effective weed management.  In an effort to monitor and inventory weed species, the Wasatch-Cache National Forest (WCNF) in cooperation with Utah State University (USU) conducted weed mapping from 2006 to 2010 on key portions of Forest System lands in northern Utah.  Mapped areas included select trails and roads as well as fires in the Logan, Ogden, Salt Lake, Spanish Fork, Pleasant Grove, Heber-Kamas, and Evanston-Mountain View Districts.  From 2006 to 2010 over 74,000 acres of land were mapped.  Of these mapped acres, 8,749 were infested with one or more species.  Targeted species included state and county noxious weeds, known invasive weeds, and selected potential invaders.  All weed infestation data were recorded as polygons on Juniper System’s Archer GPS units with a minimum detection target size of 0.001 acres.  The most abundant species mapped, in terms of total number and size of infestations, are houndstongue, Canada thistle, lesser burdock, dyers woad, musk thistle, and dalmatian toadflax.  However, it is important to note that these species were not all uniformly distributed across districts.  Mapping was also vital in identifying new invaders such as Russian and spotted knapweed, tree of heaven, perennial pepperweed, oxeye daisy and scentless chamomile on high value recreation areas.  Knowing the location and distribution of weed species enables land managers to efficiently allocate time and funds in creating and implementing an effective weed management plan.

In the summer of 2002 an initial inventory of noxious and invasive weeds was conducted in Dinosaur National Park. Weed mapping crews used GPS units to record the species, location, area, and density of infestations. Priority was given to areas that were known to have been previously inhabited, historical sites, and disturbed areas. Approximately 3,200 acres in two different areas of the park were inventoried and of those acres 15 percent of the land was infested with invasive weeds. Almost 100 acres were treated from 2006-2010 with aminopyralid at 1.5 oz ai/A for Russian knapweed and Canada thistle. In 2007 and 2008 goats were used to graze infestations followed by aminopyralid treatment. Treatments focused on containment of infested areas and shrinking infestation perimeters. Russian olive and saltcedar were treated by cut stump applications of triclopyr. In 2010 weed mapping crews re-mapped the areas mapped in 2002 to determine management success. Data showed a decrease of Russian knapweed in treated areas by 79 percent from 2002 to 2010.  Saltcedar also decreased by 74 percent, Canada thistle by 55 percent, and Russian olive by 89 percent. Other non-target invasive species also decreased in treated area. The untreated area of the park showed an increase in population and/or canopy cover in Russian knapweed and saltcedar as well as an increase in other non-target invasive species. Overall, the areas that were treated showed a 76 percent decrease in infestation from 2002 to 2010.

Russian knapweed (Acroptilon repens, ACRRE) is a long-lived, creeping perennial weed that reproduces primarily from adventitious root buds.   ACRRE rapidly colonizes and forms dense monocultures on pasture, rangelands, roadsides, and disturbed areas.  ACRRE is highly competitive due to its vigorous creeping root system, dense canopy, and allelopathic properties.  Currently, the best management strategy for long term ACRRE control includes the combination of mechanical, cultural, and chemical control.  Single control strategies such as mowing, re-vegetation, or herbicides applied alone are usually insufficient.  Rangeland that is dominated by ACRRE is often devoid of desirable plants.  Herbicides may be only a temporary fix to prevent ACRRE re-invasion if there are no competitive plants to occupy bare ground once occupied by ACRRE.  This study was designed to investigate re-establishment and competitiveness of native grass, shrub, and forb species and their response to herbicides.  The allelopathic affects ACRRE has on seedling establishment was also investigated.  Aminocyclopyrachlor (MAT at 0.5, 1, or 2 oz ai/A) and aminopyralid (1.8 oz ai/A) treatments were sprayed on May 14, 2009 and seeded on April 2010 to provide 12 months of herbicide decomposition before native seedling emergence.  Metsulfuron was added to herbicide treatments to control hoary cress (Cardaria draba; CARDR).  Handpull plots were sprayed twice in 2009 with glyphosate to decrease the number of handpulling events.  These plots were handpulled three times during the 2010 growing season.  Forb and shrub species were drilled in separate blocks from grass to ease in plot maintenance.  The study was a split-split plot design with 4 replications.  Native forb and shrub density, establishment rate, richness, and grass biomass tended to increase with the increase in ACRRE control.  Forb and shrub density counts was conducted in two drill rows that were 10 feet long in August 2010 and data were converted to plants/m².  ACRRE control increased with increasing MAT rates.  Establishment ratings derived from density counts were used to evaluate success or failure of drilled species (0% establishment or 0 plants/m² = failure; 100% or >11 plants/m² = excellent establishment).  With the exception of yarrow (Achillea millefolium) and gayfeather (Liatris Punctata), all forbs and shrubs in checks failed to establish (0% and 0 plants/m²).  Virtually no native forbs or shrubs established in untreated check plots.  This illustrates how highly competitive ACRRE is with seedling plant establishment and the negative effects ACRRE allelopathy may have on germination of other plant species.  MAT (2 oz ai/A) treatments had fair to excellent forb and shrub establishment (50 to 100%, 2 to >11 plants/m²).  Species richness (number of species present per unit area) increased with increasing ACRRE control.  There were 10 forbs, 4 shrubs and 2 grass species that were seeded (16 species total).  Total species richness in checks was three of which two were grass species.  In contrast, species richness with aminopyralid or  MAT (2 oz ai/A) was 11 or 15 species, respectively.  MAT (2 oz ai/A) provided excellent establishment for 5 of the 10 forb, 2 of 4 shrub, and both grass species.  Slender wheatgrass (Elymus trachycaulus, ELYTR) and Western wheatgrass (Pascopyrum smithii, PASSM) density and frequency counts were determined along 1 meter long quadrats when grass seedlings first emerged in May 2010.  Grass biomass was harvested in August 2010.  Forbs were not harvested in 2010 to prevent injury and disruption of flower and seed production.  There were no differences between grass densities in sprayed vs. check plots when seedlings first emerged in May 2010; however, grass was almost non-existent in check plots by the August 2010 harvest.  Grass biomass in checks was 0 to 27 lb/A and 565 to 3,329 lb/A in herbicide treatment plots in August 2010.  ACRRE biomass and control was consistently higher in PASSM plots verses similar ELYTR treated plots.  This resulted in slightly higher ELYTR biomass and establishment than PASSM from similar treatments.  ACRRE control in forb plots tended to be lower than in similar treated grass plots.  ELYTR and PASSM biomass increased with increasing MAT rates and the subsequent increase in ACRRE control.  Forbs, shrubs, and both grass species established well where ACRRE was controlled and failed where ACRRE was not controlled.  Although handpull plots were kept relatively weed free during the 2010 growing season there was significantly less grass biomass than all but MAT at 0.5 oz ai/A.  This treatment had poor ACRRE control (26 to 37%).  This was evident in a similar study conducted by CSU where grass established poorly where ACRRE roots were not controlled in handpulled plots.    This study has also shown that tillage or intense cultivating likely is not necessary to establish drilled forb, shrub, and grass in previous dense stands of ACRRE.  This particular study site had sandy loam soils.  Seedling establishment may be more difficult in heavy soils with dry climate where herbicides and ACRRE allelochemicals potentially break down slower.  Cultivation and delayed planting dates may be necessary at these sites.  Evaluations in this study will continue in 2011. 

Predicting the wildland's susceptibility to leafy spurge invasion is ground in ecological theory where plant occurrence is related to plant community productivity and climate factors.  The idea for predicting landscape susceptibility to leafy spurge was first explored by Hamilton, Lachowski and Campbell in 2006 and later refined by E. Raymond Hunt, Jr. Their work used a Weed Invasion Susceptibility Prediction (WISP) developed by Gillham et al in 2004.  These occurrence models indicate the extent of the expected invasion and in the case of leafy spurge may indicated 35 to 40% of a county is highly susceptible.  Past experience shows the best site for leafy spurge growth may not be the site receiving the seed.  Over 50% of known infestations in southeastern Idaho are within 500 m (1600 ft) of a highway or 100 m (320 ft) of a road (streets, local and farm roads).  For streams and rivers 30% of the infestations known in southeastern Idaho are within 200 m (640 ft) of water.  If the buffer area around the water feature is expanded to 500 m (1600 ft) then 43% of the infestation is found.  Combining both roads and water with 200 m (640 ft) buffer yields 69% of the known leafy spurge infestations and 75% when combined feature includes a 500 m (1600 ft) water feature buffer.  The high occurrence within a few meters of transportation routes and water suggest seed or roots transport is important for determining the occurrence of leafy spurge.

Leafy spurge is a serious weed problem in North America infesting over five million ha of rangeland and pasture. Imazapic is commonly used for leafy spurge control as a fall treatment only, because spring applications do not provide satisfactory control. Saflufenacil is a new herbicide being primarily developed for pre-plant and PRE broadleaf weed control in field crops and non-crop areas. Our hypothesis was that there might be synergism between imazapic and saflufenacil if applied in spring. Previous studies conducted during springs of 2007 and 2008 in NE determined the best tank-mix ratio of the two herbicides for leafy spurge control at about 25 g/ha of saflufenacil and 105 g/ha of imazapic. Similar rates of the two herbicides were selected for a regional study across five locations, including NE (two locations), CO, ND, and WY in 2010. The treatments included two saflufenacil (25 and 50 g/ha) and two imazapic (70 and 105 g/ha) rates applied alone, or in combination with each other. Results of the regional study confirmed our previous results, indicating that saflufenacil rate of about 25 g/ha tank-mixed with either 70 or 105 g/ha of imazapic applied in spring provided 90% control of leafy spurge for at least 90 DAT. Additional efficacy evaluation is needed (e.g., 365 DAT) to confirm the long-term synergy. sknezevic2@unl.edu

Bromus tectorum (cheatgrass) is one of the most widespread invasive species in the western United States. In sagebrush steppe rangeland it alters fire frequency, soil moisture, and nutrient dynamics, decreasing value of rangeland for wildlife and livestock and increasing costs associated with wildfire and habitat restoration. Research indicates cheatgrass invasion can alter ecosystem processes promoting a persistently infested, post invasion state. We ask whether an imazapic herbicide can be used to restore ecosystem processes and promote desirable plant communities resistant to reinvasion by cheatgrass.

In July of 2008 research plots were established on eight burned and seven paired unburned sites in southeast Wyoming. Half of the sites burned within three years of plot establishment (NB) and half burned between three and twelve years of plot establishment (OB). Following baseline data collection, plots received either a treatment of 5oz/ac (148ml/0.4ha) imazapic or no treatment (controls). In 2009, plant functional group biomass was reassessed as was vegetation carbon and nitrogen content and soil nitrate and ammonium mineralization rates.

Cheatgrass biomass was reduced by imazapic treatment in NB and OB treatment plots, but no reduction was observed in NB and OB control plots. Plant available ammonium was similar amongst treatments, while levels of plant available nitrate were elevated in imazapic treated burned and unburned plots of all ages.

No reduction in cheatgrass biomass between NB and OB controls suggests limited recovery through natural processes. Although reduced cheatgrass biomass was achieved in treated plots, elevated available nitrate in these plots is cause for concern. If nitrate remains high beyond the time imazapic is active in the soil, it can become an ecological driver for reinvasion by cheatgrass. High levels of nitrate have been observed beneath cheatgrass communities relative to native communities and identified as a potential explanation for cheatgrass persistence. Mechanistically, annuals sacrifice environmental stress tolerance for fast growth through rapid nitrogen uptake. When resources are reduced the competitive advantage may shift toward perennial species. Further work will be conducted to determine whether perennials reduced nitrogen levels before the expected loss of imazapic activity.

ABSTRACT

Five Years Annual Grass Efficacy Evaluations Using Rimsulfuron and Sulfometuron-methyl plus Chlorsulfuron in Colorado and Wyoming.  Jim T. Daniel, Consultant DuPont Land Management, Keenesburg, CO, John D. Cantlon and Ronnie G. Turner, Dupont Land Management, Lakewood, CO and Memphis, TN, George Beck and James Sebastian, Colorado State University, Fort Collins, CO.

Annual grass control with rimsulfuron and sulfometuron methyl premixed with chlorsulfuron in established perennial grasses was evaluated in 16 trials conducted across Colorado and Wyoming.  Most of the evaluations were on downy brome (Bromus tectorum L.).  Control of feral rye (Secale cereale L.) and annual wheatgrass (Eremopyrum triticeum (Gaertn) Nevski) was also evaluated.  All trials were applied with a standard small plot sprayer equipped with flat fan tips.  Seven of the evaluations were replicated, randomized complete block trials and nine were nonreplicated demonstration trials containing three treatments and located across both states.

Both rimsulfuron (formulated as MATRIX®) and sulfometuron methyl premixed with chlorsulfuron (formulated as LANDMARK®) provided excellent control of downy brome across all trials.  In these trials, both fall and spring applications were effective in controlling downy brome.  Both products were also effective in controlling annual wheatgrass.  Rimsulfuron gave good initial control of feral rye when applied either late summer or early spring.   Feral rye evaluations dropped to the mid 70% range of control by late July.  Late spring applications were not effective for feral rye control.

Perennial grasses in general were not harmed in most trials.  There was some stunting especially from higher rates but the perennial grasses did recover from the stunting usually by the end of the growing season.

   Tall larkspur is an important perennial weed on high elevation rangelands in the western United States where cattle are grazed because of significant livestock losses from toxic alkaloids in the plant. A new synthetic auxin herbicide, aminocyclopyrachlor, was evaluated for tall larkspur control alone and in combination with chlorsulfuron at multiple rates (17.5, 35, 70, 140 and 315 g ai/ha of aminocyclopyrachlor) at a high elevation infestation in the Big Horn Mountains of Wyoming. Aminocyclopyrachlor-containing treatments were compared with picloram at 1120 g ai/ha and metsulfuron-methyl at 63 g ai/ha. Treatments were replicated four times in 3 m x 12.2 m plots set in a randomized complete block design.  Herbicides were applied at 187 liters per hectare with a CO₂-powered sprayer and 3 m boom with six 8002 nozzles on June 18, 2010. All treatments contained a non-ionic surfactant at 0.25% v/v. Sixty days after spraying, percent control (visual estimate) and mortality of tall larkspur, and percent injury (visual estimate) of grasses were recorded. A four parameter log-logistic model was used to evaluate tall larkspur control and grass injury in response to rates of aminocyclopyrachlor.  Aminocyclopyrachlor alone and aminocyclopyrachlor + chlorsulfuron provided maximum tall larkspur control of 88% and 85%, respectively; which did not differ statistically. Metsulfuron methyl and picloram provided 92% and 27% control, respectively.  These results suggest that aminocyclopyrachlor alone may provide satisfactory control of tall larkspur, but it will be necessary to reevaluate this site 1 year after treatment to determine if the control is lasting.

Aminocyclopyrachlor, a synthetic auxin, has recently been registered for non-crop applications.  One potential future use of aminocyclopyrachlor is invasive weed management in reclamation and restoration situations.  A greenhouse study was conducted in 2010 at the University of Wyoming to investigate the seedling response of 27 species accessions or cultivars and 2 exotic weeds to aminocyclopyrachlor.  Aminocyclopyrachlor was applied at rates of 20, 40, 80, 160, 320, and 640 g/ha 30 days after planting when grasses reached the 3 to 5 leaf stage and forbs and shrubs were less than 5 cm in height.  There were 7 replicates and all treatments included a nonionic surfactant at 0.25% v/v. Herbicide treatments were applied in a spray chamber delivering 187 l/ha at 276 kPa.  A four parameter log-logistic model was used to estimate the dry weight reduction in response to aminocyclopyrachlor rate.  Russian thistle biomass was reduced 99% at 180 g/ha.  At the same rate, reduction in grass biomass ranged from 11 to 49%. Variation in growth reduction by aminocyclopyrachlor was observed among genera and species, and even among germplasm within a species.  At 180 g/ha, growth of all flax and sagebrush species was reduced ≥81%.  If aminocyclopyrachlor were used in a reclamation or restoration situation for postemergence control of Russian thistle, most of the grasses in this experiment appear to be fairly tolerant; whereas the selected sagebrush and flax species were highly susceptible at this early growth stage even at low rates.

   Recent research at Colorado State University has confirmed hybridization in the field between invasive populations of yellow toadflax (YT) and Dalmatian toadflax (DT). Hybrid toadflax populations could pose a greater threat than either parent species if the hybrids occupy different niches or have a greater adaptive ability than the parents. Earlier results from controlled interspecific crosses showed greater seed set and seedling viability seed from YT x DT crosses than DT x YT. This suggests asymmetric gene flow in naturally hybridizing toadflax populations, with a greater likelihood of invasive YT populations acquiring DT genes via introgression than the reverse. In most angiosperms chloroplasts are maternally inherited, so species-diagnostic chloroplast DNA markers can determine the identity of a toadflax hybrid’s maternal parent and direction of gene flow. We are screening published universal cpDNA primers to identify variable chloroplast DNA regions which could be used as a species diagnostic tool. After amplification and sequencing, we selected chloroplast regions trnT(GUC)/trnD(GGU), trnL, and rpL16 as likely candidates for chloroplast marker development.  We have identified an AluI restriction site in region trnT/trnD, that distinguishes between YT and DT cpDNA, and we are using this to screen additional field-collected hybrids.

Reestablishing native perennial grass species such as bluebunch wheatgrass (Pseudoroegneria spicata) is one management tool for restoring lands dominated by cheatgrass (Bromus tectorum), an exotic annual grass.   Yet, reseeding perennial grasses is often unsuccessful due to cheatgrass’ early emergence time and ability to preempt and quickly utilize resources.  We conducted a greenhouse study investigating the role of relative size and nitrogen (N) availability in competitive interactions between cheatgrass and bluebunch wheatgrass, with the intent of improving rangeland revegetation practices.  We hypothesized that cheatgrass growth is more responsive to increased N than bluebunch wheatgrass and that competitive ability of bluebunch wheatgrass seedlings increases with seedling size relative to cheatgrass.  In an addition series experiment, we combined four densities of each species, three size cohorts of bluebunch wheatgrass (seeds, two-leaf, and four-leaf seedlings), and two N treatments (ambient and high) for a total of 96 experimental units replicated four times.  For both species, we predicted individual average biomass as a function of densities of each species, bluebunch wheatgrass size cohort, and N treatment.  Cheatgrass responded to added N by accumulating more biomass than bluebunch wheatgrass. As predicted, when the species were planted simultaneously cheatgrass suppressed bluebunch wheatgrass growth, but cheatgrass had little effect on larger bluebunch wheatgrass seedling biomass across both N treatments.  Furthermore, the larger bluebunch wheatgrass seedlings suppressed cheatgrass growth.  These results suggest that techniques that allow perennial grasses to achieve a size advantage over cheatgrass may increase the chance of reseeding success, even when resource availability is elevated.

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.

The Western United States, has seen booming population growth resulting in great changes in the landscape and agriculture practices.  Changes include transformation of rangeland and farms to houses, or to ‘ranchettes,’ and an influx of newcomers either from out of the area or land owners without a rural background, often lacking knowledge of local vegetation management practices.  Introduction of invasive weeds often comes with disturbances from new roads and home construction, and from inadvertent seed deposition from livestock, bedding straw and machinery brought in from other parts of the country.  This introduction of invasive plants creates an education and outreach challenge for resource specialists striving to disseminate most current information on plant identification and management recommendations.   When facing the issue of a changing landscape and degrading forces such as invasive plant species, land managers need time sensitive and cost effective solutions to these problems.  Field research results do not often reach target audiences due to decreasing state extension budgets.  This economic shortfall has meant that training and educating land managers and extension personnel has suffered and the sharing of those ideas is often lost in scientific journals. 

A proposal has been submitted to the Western Society of Weed Science to create a subgroup or committee within the society to address these issues.  The discussion will take place at the Range and Natural Areas symposium under the title  "Extend invasive weed management with novel technologies and collaborative applied research networks".

The proposal includes the following goals:

·         Create a venue that bridges the gap between researchers, extension specialists and land managers by structuring a program that encourages cooperation and collaboration with a focus on invasive weed species management and restoration techniques in natural areas, rangeland and pasture.

·         Identify and prioritize most important issues confronting land managers, and apply research necessary to address such issues by establishing locations for research & demonstration sites with private landowners, open space agencies and on local, state and federal lands.

·         Conduct research that focuses on range and pasture restoration techniques and judicious use of herbicides and alternative weed management methods.

·         Disseminate results of research and demonstration sites through tours, publications and a website.

·         In short, help to fill the gap left by declining state extension budgets and activities, and encourage land managers to actively participate with researchers in establishing best management practices relating to invasive plant management and restoration techniques.

Weedy spurges (Euphorbia hyssopifolia, E. maculata, E. nutans and E. prostrata) are among the most difficult to control weeds in nursery containers in the desert southwest. Nursery managers complain that available granular herbicides are ineffective.  Dithiopyr,  trifluralin + isoxaben and trifluralin + isoxaben + oxyfluorfen were topdressed into one gallon nursery containers without a crop on 07 September 2010 at 150 and 200 lbs granular product./A; dimethanamid + pendimethalin was applied on the same date at 150 lbs. granular product/A only.  Chemical treatments were compared to an untreated control (UTC). Spurge control was compared in containers with a regular planting medium composed of 2 parts fine mulch, 2 parts volcanic cinder and one part coarse mulch to containers with regular planting medium plus a two inch coarse mulch topdress. Weekly spurge germinations were counted and percent of the container covered by spurge mat was calculated at 30 days after treatment (DAT) and 60 DAT. Data was analyzed using JMP 8.0.2. There was no improvement in spurge control applying the higher rate of dithiopyr, trifluralin + isoxaben or  trifluralin + isoxaben + oxyfluorfen. The addition of the coarse mulch topdress improved spurge control in trifluralin + isoxaben and trifluralin + isoxaben + oxyfluorfen. At 60 DAT, greatest control was achieved using dimethanamid + pendimethalin, although trifluralin + isoxaben + oxyfluorfen and dithopyr performed better than the UTC.

Weeds, including lambsquarters, nightshades, and field bindweed remain a problem in tomatoes and melons.   Sulfentrazone is currently labeled for use in cabbage, beans, and several other crops, and initial studies indicated that tomato and melon crops might be tolerant.   Sulfentrazone was compared with standard treatments in transplanted processing tomato in 2007, and 2010, and in cantaloupe, honeydew and watermelon, in 2007 to 2010.   In spite of injury from sulfentrazone applied preemergence at 112 g/ha, tomato yields were the highest, and broadleaf weed control was equal or better than the standard treatment of rimsulfuron.    Melon injury exceeded 50% when sulfentrazone was applied at 168 g/ha, but was less than 20% at 112 g/ha.  Watermelon was more tolerant of sulfentrazone than honeydew melon, and cantaloupe was the least tolerant.  Broadleaf weed control was near 100% for the entire season, when sulfentrazone was applied postplant, preemergence, and incorporated by irrigation.  Broadleaf weed control in melons declined to near 80% at eight weeks after planting when sulfentrazone was mechanically incorporated.   Control of grasses and established field bindweed was poor.  Melon yields were equal or better than standard treatments when the 112 g/ha rate of sulfentrazone was used. 

Experiments were located at the Oregon State University Woodhall Vineyard near Alpine in Chardonnay grapes in 2009 and 2010 to measure efficacy of flazasulfuron and other herbicides used in vineyards. The primary grasses present at the two sites were tall fescue (Festuca arundinacea) and bentgrass (Agrostis spp.); the primary broadleaf species present were bristly hawksbeard (Crepis setosa), spotted catsear (Hypochaeris radicata), and dandelion (Taraxacum officinale), with a small amount of clover, willow weed (Epilobium spp.), geranium present. Soil tests indicated a pH of 5.7, OM of 5.08 % (loss on ignition) and CEC of 12.1 meq/100 g of soil. The experimental design was a randomized complete block with 4 replications. All herbicides were applied with a backpack CO₂ sprayer with an XR-8003 nozzle delivering 20 GPA. The nozzle was held 10 inches from the vine row and approx 20-24 inches above the ground to create a 2 ft. spray width on each side of the row. There were 3 vines per 21 ft. long plot. In 2009, flazasulfuron was applied alone or as a tankmix with other PRE herbicides on April 2. In 2010, glyphosate at 1.375 lbs ae/A was applied first to all plots except the untreated check plot on April 7. Preemergence treatments of flazasulfuron, flumioxazin, oxyfluorfen, oryzalin, rimsulfuron were applied 2 and 6 weeks after the glyphosate.

In 2009, flazasulfuron alone on April 2 provided exceptional control of the grasses and clover. Control of bristly hawksbeard and spotted catsear was less than for the grasses. Tankmixing flazasulfuron with pendimethalin and s-metolachlor did not improve control of bristly hawksbeard; tankmixing with flumioxazin increased control of hawksbeard from 83 to 93%. In 2010, flazasulfuron following glyphosate provided very good control of all species except willow weed at 7 WAT. Willow weed control improved slightly with flazasulfuron applied at 0.045 lbs ai/A compared to 0.033 lbs ai/A. Most of the other preemergence herbicide treatments improved glyphosate efficacy, but a late application of oryzalin did not improve weed control compared to glyphosate alone. Control of willow weed dropped when flazasulfuron and flumioxazin were applied on May 24 rather than April 22, but increased when oxyfluorfen, oryzalin, and rimsulfuron were applied on May 24 rather than April 22. No effect of herbicides on vines was noted in either year.

Indaziflam for Pre-emergent Weed Control in Almonds.  Ryan Allen, Bayer CropScience, Roseville, CA.

Field efficacy studies conducted between 2004-2010 in California almond orchards have demonstrated that Indaziflam effectively controls a wide spectrum of important broadleaf and grass weed species when applied preemergence.  Indaziflam has been evaluated throughout the almond growing region of California by University, private, and Bayer CropScience researchers at various rates and timings, as well as in tank mixes with many common adjuvants and other herbicides.  The results of these studies demonstrate that an application of Indaziflam at 73 g ai/ha (5 fl oz/A) can effectively control a broad spectrum of grass and broadleaf weeds for up to 6 months, although control of 10 months or more has been observed in some cases.  Indaziflam will be marketed as Alion^TM upon registration, which is anticipated in 2011.

Persistent, perennial weeds such as field bindweed (Convolvulus arvensis) typically require an integrated approach for successful management.  Quinclorac has been shown to effectively reduce field bindweed by up to 85% in small fruit systems, with minimal risk of crop injury.  Another strategy for field bindweed management is the use of biological control agents.  There are currently two arthropods registered for use in the U.S., a defoliating moth and a gall-forming mite.  The mite, Aceria malherbae, has proven to be particularly effective in dryland states such as Texas, Oklahoma, and Western Colorado.  However, successful recovery of the mite in the Pacific Northwest has been limited.  This study evaluated the efficacy of A.malherbae both alone and in conjunction with quinclorac applied at varying rates.  Experiments were placed at two different sites; established blueberries in Lebanon, OR., and first year blackberries near Dayton, OR.  Plots were designed as completely randomized blocks, with 4 replications each.  Application method of the mites was the first experimental factor; herbicide rate was the second factor.  Plants were evaluated using 6 visual parameters to estimate presence of the mite and herbicide effectiveness.  In blueberries, percent control averaged 77% and did not differ between 0.42kg ai/ha and 0.84kg ai/ha rates.  Quinclorac reduced flowering by 40% in first year blackberries and control averaged 38%.  Interactions between Aceria and quinclorac varied between sites. 

Meadowfoam (Limnanthus alba Hartw. ex Benth.) seed meal, a by-product of meadowfoam oil extraction, has characteristics that suggest its potential utility in agriculture as a soil amendment to enhance plant growth and possibly suppress soil pests. The presence of glucosinolate degradation products which are produced by the enzyme myrosinase are thought to be directly or indirectly responsible for the weed suppression induced by meadowfoam seed meal. Greenhouse and laboratory studies were conducted to evaluate the effect of three different forms of meadowfoam seed meal: seed meal, activated seed meal, and seed meal pellets on the suppression of lettuce emergence and growth. The three formulations had different effects in regards to seedling emergence and growth, time course of activity, and consistency in the concentrations of active compound in the soil. Meadowfoam seed meal in the pellet form produced highly variable concentrations of glucosinolate and its breakdown products in soil samples. The soil amended with activated meadowfoam seed meal provided the best results for suppression of lettuce emergence and growth. The effect lasted less than 6 days after seed meal application; therefore, it may be possible to use meadowfoam seed meal preplanting for weed control. Research is needed to determine the activity of meadowfoam seed meal under field conditions.

Herbicide combinations were evaluated for weed control in ornamental bulbs at Mount Vernon and Puyallup, Washington in 2008 through 2010.  Tulip (cv. ‘Ile de France’), daffodil (cv. ‘Dutch Master’), and iris (cv. ‘Blue Diamond’) bulbs were planted in October, 2008 and 2009 and dormant-season herbicides were applied in early winter prior to emergence of bulb foliage.  Tested herbicides at the Mount Vernon were napropamide, oryzalin, mesotrione, s-metolachlor, and pendimethalin applied alone at two rates each or in several two-way combinations.  Herbicides tested at Puyallup were napropamide and oryzalin at two rates each.  Weed control and crop injury were evaluated through the growing season.  Flower number and stem length were recorded at full bloom for each species.  At the end of the growing season, bulbs were harvested, cleaned, sized, counted, and weighed.  Weed control at Mount Vernon during March and April generally exceeded 90% for most treatments in 2009 and 2010.  By late April, 2009, weed control was diminished with mesotrione, napropamide, and pendimethalin applied alone.  Combination treatments continued to provide > 90% weed control through April, 2009.  In 2010, all treatments except for the low rate of pendimethalin provided > 90% weed control in late April.  By May, only oryzalin alone or in combination was still providing > 90% weed control.  Weed control at Puyallup during 2009 and 2010 exceeded 88% for all treatments in early March.  However, by late March, 2009 weed control with napropamide treatments was significantly poorer than with oryzalin.  By early May, 2010 only the highest rate of oryzalin exceeded 87% weed control.  No treatment caused visible foliar or floral injury to any bulb species at either location in either year.  There were no significant differences in yield parameters due to herbicide in any of the three bulb species at either location in either year.

Topramezone is under development by BASF for weed control in cool season turfgrasses. Topramezone is a HPPD inhibiting herbicide that controls weeds by inhibiting carotenoid biosynthesis. Topramezone provides broad spectrum control of both broadleaf and grass weeds. Extensive field testing has shown that major cool season turfgrass species exhibit excellent tolerance including: Kentucky bluegrass, fine and tall fescue, and perennial ryegrass. Tolerance levels in most warm season turfgrass species has been shown to be poor with the exception of centipedegrass, which exhibits a high level of tolerance. Field studies conducted in cool season turfgrass with topramezone have demonstrated effective control of key weed species such as white clover, Veronica spp, crabgrass and goosegrass. Additional research has demonstrated that topramezone also offers selective control of key perennial grasses such as bermudagrass when mixed with triclopyr. Effective control of perennial grasses was shown to require a multiple application approach for best results. Control of bermudagrass with topramezone plus triclopyr applied in sequential programs provided superior control to that observed with either herbicide used alone. In addition, the visual bleaching effect of topramezone on bermudagrass was substantially reduced when applied in mixtures with triclopyr. The mixture’s aesthetic benefit of reduced bleaching combined with the enhanced control of weedy bermudagrass should be a valuable tool for cool-season turfgrass managers.

Weeds are a significant pest management problem in peppermint grown for oil production across Oregon and the use of herbicides to control these weeds is the primary weed management tool utilized by peppermint growers.  Experiments were conducted from 2008-2011 in growers’ fields throughout the Willamette Valley and at Hyslop Research Farm in Corvallis, Oregon to evaluate the tolerance of peppermint grown for oil to herbicides that are not currently registered for this use pattern.  The herbicides evaluated included pyroxasulfone, ethofumesate, saflufenacil and carfentrazone.  Pyroxasulfone was initially evaluated for efficacy in a noncrop experiment at 0.0224 and 0.045 kg ai/ha.  Pyroxasulfone at 0.103 and 0.206 kg ai/ha were evaluated on dormant, 5% and 10% emerged, 0.6, 2.5, 5.1, 7.6, and 45.7 cm peppermint and in a post harvest situation in double cut peppermint.  Ethofumesate was evaluated in dormant, 5.1, 12.7, 15.2, and 25.4 cm peppermint and in a post harvest situation in double cut peppermint with rates of 0.56, 1.12 and1.68 kg ai/ha.  Saflufenacil was evaluated in dormant peppermint at rates of 0.018, 0.0247 and 0.038 kg ai/ha and 0.0493 kg ai/ha was evaluated in a post harvest situation in double cut peppermint.  Carfentrazone at 0.0168 kg ai/ha was evaluated on 20.3 and 50.8 cm peppermint and in a post harvest situation in double cut peppermint.  The experimental design of all experiments was a randomized complete block with 3 or 4 replications.  Visual evaluations of crop injury and weed control were taken when crop or weeds were present and fresh weight and oil yields were taken on the studies that were conducted in crop situations.  Crop tolerance of peppermint grown for oil from all preemergent and postemergent applications of ethofumesate in 2008, 2009 and 2010 and saflufenacil in 2009 and 2010 was excellent.  Peppermint was injured (30%) in 2008 with the highest rate of pyroxasulfone evaluated (0.206 kg ai/ha) when applied to dormant and 0.6 cm peppermint.  Carfentrazone did injure the peppermint in 2010 when applied to 20.3 cm or taller peppermint; however, the peppermint did recover from the injury.  Pyroxasulfone applied at 0.103 kg ai/ha preemergence to weeds and incorporated with water provides good control of redroot pigweed (Amaranthus retroflexus), annual sowthistle (Sonchus oleraceus), common groundsel (Senecio vulgaris), and prickly lettuce (Lactuca serriola) with crop safety.  Ethofumesate applied at 1.68 kg ai/ha on moist ground to actively growing peppermint and preemergence to pigweed provides crop safety and weed control.  Saflufenacil, while safe on the crop, has not provided weed control in the situations it has been evaluated.  The high rate (0.0493 kg ai/ha) applied post harvest in a double cut field may be the best fit for saflufenacil.  A timing study with carfentrazone is needed to determine the safest application timing.  Registration of pyroxasulfone, ethofumesate and carfentrazone would provide expanded control of many weeds in peppermint.

Corn gluten meal and mustard seed meal have been shown to have the ability to control weeds when applied pre-emergence. Other protein meals such as blood and poultry meal are used as organic nitrogen sources and as growth promoters among organic gardeners and farmers. These products, like corn gluten meal, are high protein meals typically used as animal feed supplements. A greenhouse study was conducted to: 1) determine whether animal protein meals had herbicidal activity; 2) understand what rates of protein meals would kill weeds; and 3) determine if there is a weed species response to these meals. This screening trial examined four protein meal sources: blood meal, poultry meal, feather meal, and sardine meal; applied at three rates: 2,240, 4,480 and 6,720 kg/ha. The experimental design was a three by four factorial randomized complete block design with four replications. An untreated control was included to compare the protein meal treatments. Weed species evaluated were common lambsquarters (CHEAL), kochia (KCHSC), redroot pigweed (AMARE), hairy nightshade (SOLSA), annual sowthistle (SONOL), Russian thistle (SASKR), green foxtail (SETVI) and barnyardgrass (ECHCG). A soil mixture consisting of a 4:1 ratio of field soil and potting mix was used for growing the weeds. Two kg of soil mix was added to 25.4 by 50.8 cm plastic trays in preparation for planting. Eight grooves evenly spaced across each tray were made for planting the seed. Each required amount of protein meal was mixed with 680 gm soil mix and carefully placed over the weed seed. Weed seedling emergence and weed control were evaluated 21 days after planting (DAP) and 28 DAP. In addition, weed seedlings were harvested 28 DAP and dry weights recorded. All data are presented as a percent of the control. KCHSC was not controlled very well by any of the protein meals and there was no difference in KCHSC dry weight between protein meals or rates. The meal dry weights pooled across protein meals and application rate averaged 91% of the control. AMARE dry weights pooled across application rate averaged 35% of the control, with no difference among protein meals. In response to application rate pooled across protein meal, AMARE dry weights were 60, 20 and 7% of the control at 2,240, 4,480 and 6,720 kg/ha, respectively. There was a significant protein meal by application rate interaction for CHEAL dry weight. CHEAL dry weight was reduced more by the 2,240 kg/ha rate of blood meal than any other protein meal applied at 2,240 kg/ha rate. At 6,720 kg/ha, CHEAL dry weight was reduced to 4, 8, and 8% of the control with poultry, blood, and sardine meal, respectively. However, with feather meal, CHEAL dry weight was reduced to only 40% of the control with feather meal. SETVI dry weight was reduced most by feather meal and poultry meal, averaging 5 and 14% of the control, respectively. Averaged across application rate, sardine and blood meal reduced SETVI dry weight to 25 and 33% of the control. There was a significant protein meal by application rate interaction for SASKR dry weight. SASKR dry weight was most affected by sardine meal and least affected by poultry and blood meal at the 2,240 kg/ha rate. Dry weight of SASKR was not statistically different at the 4,480 and 6,720 kg/ha rates of all four protein meals and averaged 21% of the control. ECHCG dry weight appeared to be the least affected weed by the protein meals. ECHCG was least affected by feather meal, with a dry weight that was 128% of the control. ECHCG dry weight from the poultry, blood and sardine meal treatments were not statistically different and averaged 80% of the control. ECHCG dry weight in response to application rate pooled across the protein meals was 130% of the control at 2,240 kg/ha. There was no difference in dry weight between the 4,480 and 6,720 kg/ha application rates pooled across meals and averaged 73%. SOLSA was not affected more by one protein meal than another. However, SOLSA dry weight in response to application rate pooled across protein meals was 55, 10 and 11% of the control when applied at 2000, 4000 and 6000 lb/A, respectively. SONOL appeared to be the most sensitive of the eight weed species evaluated. Average SONOL dry weight pooled across protein meal and pooled across application rate was only 2% of the control. KCHSC appeared to be the most tolerant of all weed species evaluated while SONOL was the most susceptible to the protein meals.

Pyroxsulam is the active ingredient in Dow AgroSciences’ PowerFlex® herbicide.  PowerFlex is labeled for use in winter wheat.  The currently available PowerFlex formulation contains 7.5% of active ingredient in a water dispersible granule.  A potential new formulation being evaluated contains 13.1% pyroxsulam.  The studies described herein were designed to compare crop tolerance and weed control of the two formulations.  Crop tolerance studies were conducted at 6 and 7 locations in 2009 and 2010, respectively.  Each formulation was applied at 18.4 g (1X) and 36.8 g (2X) pyroxsulam/ha with nonionic surfactant and ammonium sulfate.  In each year, only 1 location showed differences between formulations for crop tolerance.  In both cases, formulation differences occurred only with the 2X rate of pyroxsulam.  In 2009, the differences persisted throughout the growing season, while in 2010 differences were transitional and were not observed in ratings made later than 3 days after application.  Generally, injury ratings did not exceed 10% although there were a few exceptions.  Separate grass weed control studies were conducted at 13 locations in each year.  Pyroxsulam rates for the formulation comparison were 13.8 and 18.4 g ai/ha applied with nonionic surfactant and ammonium sulfate.  Targeted grasses were Italian ryegrass and downy brome.  Differences in grass control between formulations only occurred in 6 of the 26 locations.  Moreover, there was not a consistent pattern in which formulation provided better control nor were there consistent differences within or between rates.  Thus, in summary both formulations performed equally well for weed control and crop tolerance.

The objective of this study was to evaluate the effectiveness of Tribenuron and Carfentrazone alone and in tank mix combinations including Dicamba, MPCA, and 2,4-D at different rates to control different broadleaf weeds and how it affected the injury to common hard red spring wheat.  The study was conducted at three different locations; Ducor, Porterville, and Visalia in Tulare County, California.  The treatments were applied with a CO₂ backpack at a speed of 4 mph.  The nozzles were 8002vs flat fans with a spray pressure of 40 psi and a volume of 15 GPA.  The plot sizes for all three locations were 8 feet by 30 feet with four replications. 

            The Visalia location was sprayed on January 10, 2011 with a temperature of 45^ºF and a wind speed of 0 to 2 MPH.  The wheat was 5 to 12 inches tall and at the 5 to 7 leaf stage.  The weeds present at the time of the application were burning nettle (Urtica dioica) which was 0.5 to 1" dia, common chickweed (Stellaria media) which was 0.5 to 1" dia.  The Ducor location was sprayed on January 28, 2011 with a temperature of 48^ºF and a wind speed of 0 to 3 MPH.  The wheat was 3 to 8 inches tall and at the 4 to 6 leaf stage.  The weeds present at the time of the application were burning nettle (Urtica dioica) which was 0.25 to 1" diameter (dia) (0 to 0.25 plants/sq. ft., ), common chickweed (Stellaria media) which was 1 to 1.5" dia. (0 to 3 plants/sq. ft.), shepherd's purse (Capsella bursa-pastoris) which was at 0.25 to 0.5" dia. (18 to 20 plants/sq. ft.), fiddleneck (Amsinckia spp.) which as at 0.5 to 2.5" dia. (5 to 10 plants/sq. ft.), filaree (Erodium spp.) which was at 0.25 to 3" dia. (4 to 6 plants/sq. ft.),  malva (Malva parviflora) which was at 0.5 to 2.5" dia. (0.25 to 1 plants/sq. ft.), and wild oats (Avena fatua) which was 1 to 2.5" tall (5 to 8 plants/sq.ft.).  The Porterville location was sprayed on February 8, 2011 with a temperature of 55°F and a wind speed of 0 to 4 mph.  The wheat was 4 to 6 inches tall and was at a 3 to 5 leaf stage.  The weeds present at the time of the first application were burning nettle (Urtica dioica), common chickweed (Stellaria media), and fiddleneck (Amsinckia spp.). 

            The results of this study demonstrated some variation between weeds, treatments, and location.  For the Ducor locations the treatments showed moderate control (60-70) over fiddleneck, chickweed, shepherd’s purse, common groundsel, filaree, and malva 14 days after treatment.  At the Porterville location Carfentrazone alone treatments showed excellent control of burning nettle 7 days after treatment.  The treatment combinations with Tribenuron and Carfentrazone showed excellent control over burning nettle as well, except for the treatment with the low rate of Tribenuron and high rate of Carfentrazone which only gave moderate control over burning nettle 7 days after treatment.  All of the treatments gave fair control over common chickweed 7 days after treatment, except for the high rate of Tribenuron and the high rate of Carfentrazone which gave excellent control over common chickweed.  The treatments with Carfentrazone alone gave excellent control of fiddleneck 7 days after treatment.  All of the treatments with the Tribenuron and Carfentrazone combinations showed excellent control of fiddleneck 7 days after treatment.  The injury levels were low among all of the treatments 7 days after treatment.  At the Visalia location all of the treatments gave excellent control of burning nettle and chickweed by 28 days after treatment.  The treatments with Tribenuron alone showed extremely low levels of injury 28 days after treatment.  The treatments with the Carfentrazone alone and Tribenuron and Carfentrazone combinations demonstrated the highest levels of injury, however, injury was not significant and disappeared after 30 days.  The treatments with combination of Tribenuron and dicamba, Tribenuron and 2,4-D showed low levels of wheat injury and the treatment with Tribenuron and MCPA showed no levels of injury. 

Rimfire Max was commercially introduced in the spring of 2010. It is a postemergence herbicide with the ability to control many problematic grass and broadleaf weeds in winter, spring, and durum wheat. Rimfire Max is a new formulation with ALS-inhibiting compounds mesosulfuron-methyl and propoxycarbazone sodium plus a safener, mefenpyr-diethyl. Rimfire Max has a wide application window and can be applied to wheat from 1-leaf up to flag leaf emergence. It is formulated as a 6.67% WDG and must be applied with one of several adjuvant systems. Adjuvant options include 1.75 l/ha methylated seed oil, 1% v/v basic blend adjuvant, or NIS plus UAN at 0.5% v/v and 4.7 l/ha, respectively. Results from research trials have shown that a methylated seed oil additive is the most effective adjuvant system to maximize weed control. Rimfire Max is generally tankmixed with a broadleaf herbicide such as Huskie (containing pyrasulfotole and bromoxynil) to provide broad spectrum weed control in wheat. Between 2009 and 2010, 114 trials were conducted in ND, SD, MT and MN to evaluate control of difficult to control grass weed species such as downy brome, Japanese brome, Persian darnel and ACC-ase resistant and susceptible wild oat.  Rimfire Max at 13.97 g ai/ha plus Huskie at 206 g ai/ha with 1.75 l/ha methylated seed oil (MSO) applied prior to tillering of downy brome resulted in 66% control averaged across 9 trials. Wild Oat control averaged 89 to 93 percent 30 to 60 DAT with various dicot tankmkix partners.  Persian darnel control was best with Rimfire Max + Huskie combined with MSO (91%) compared to Rimfire Max + Huskie combined with a basic blend adjuvant (87%).  Japanese brome was controlled 89 to 94 percent when Rimfire Max was combined with various dicot tankmix partners.  Control of common lambsquarters, common sunflower, wild buckwheat, kochia, Russian thistle, and wild mustard averaged greater than 96 percent.

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

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

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

Previous greenhouse studies have shown that common lambsquarters and giant ragweed plants grown in an unsterile soil were more severely damaged by glyphosate than those grown in a sterile medium. The objective of this study was to determine whether soil type had an effect on the efficacy of glyphosate on Canada thistle (Cirsium arvense L.) grown from rhizomes. Rhizomes were collected from a field near the University of Wyoming greenhouse in September, 2010. Rhizomes approximately 4 mm in diameter were cut to 2 cm and planted in 10 cm pots in either greenhouse or field soil. The field soil was collected from the same field as the rhizomes. Emerged plants were sorted by size and treated with glyphosate at rates from 0 to 3.4 kg ae/ha. Visual injury ratings were taken 2 weeks after glyphosate application. Plants were harvested 3 weeks after glyphosate application and dried for 48 hours at 60°C. Data were analyzed using analysis of variance. Soil type did not have a significant impact on glyphosate efficacy based on visual injury symptoms or dry weight. The difference in these results compared to previous studies may be attributed to the fact that plants were grown from rhizomes that may have already contained soil pathogens, rather than clean seed. In the future, more studies will be necessary to determine whether there would be a different result if the Canada thistle plants were grown from seed. Other possibilities for further study include sterilizing the rhizomes prior to planting.

A field study was conducted in 2010 to quantify the effect of volunteer corn density on sugarbeet yield loss.  The objective of this study was to determine whether remote sensing or light measurements taken mid-season were correlated to sugarbeet yield loss. Volunteer corn was planted into the sugarbeet row at 0, 0.3, 0.5, 0.8, 1.2 and 1.6 plants/m². Plots were 3 m wide by 9 m long and arranged in a randomized complete block design with four replications.  Glyphosate was applied as needed to remove weeds other than volunteer corn.  Light transmittance (LT) and leaf area index (LAI) measurements were taken above and below the sugarbeet canopy within each plot on July 14.  Remote sensing imagery was taken via AEROCam on August 13 in red, green, and near infrared (NIR) bands with a spatial resolution of 0.25 m².  Spectral values were calculated for similar locations as LT and LAI measurements, and analyzed in ERDAS IMAGINE software.  Sugarbeet root yield, percent sucrose content and recoverable sucrose were measured at harvest on October 5.  Measured LAI above the sugarbeet canopy was strongly correlated with root yield and recoverable sucrose (r=-0.8319, P=0.0001 and r=-0.8039, P=0.0001 respectively). LT at the top of the sugarbeet canopy was also correlated with root yield and recoverable sucrose (r=0.9392, P=0.0001 and r=0.9184, P=0.0001 respectively).  The NIR spectral values significantly correlated with root yield and recoverable sucrose (r=0.5405, P=0.0064 and r=0.5728, P=0.0043 respectively) but the relationship was not as strong when compared to either LAI or LT.  

Small burnet (Sanguisorba minor scop) is a perennial, evergreen forb in the rosacaceae family. It is a hardy, relatively long lived forb that does well in most of North America.  There is interest in its use to extend grazing of pastures and rangelands into late fall and winter.  Two small burnet genotypes were arranged in a randomized complete block design with a split plot arrangement where herbicide treatment was the whole-plot and small burnet genotypes were the sub-plots.  Twelve treatments, untreated, clopyralid, imazamox, 2,4DB, metribuzin, aminopyralid, pendimethalin, dimethenamid-P, bromoxynil, dicamba, quinclorac, and clethodim were applied June 4, and November 11, 2009 of the establishment year.  Plots were given a visual rating of 1 to 10.  1 = complete mortality and 10 = no injury.  Seed was hand harvested and weighed.  The remaining biomass was harvested.  The dry weight seed yield was added to the dry matter yield (DMY).  Fall treatments of aminopyralid and imazamox showed the most injury reducing seed yield by 95% and 84% and DMY by 48% and 42%.   Aminopyralid caused the greatest visual injury of all the spring treatments with a rating of 5.5 compared to 9.0 for the untreated.  Fall applications of dicamba caused significant injury with a rating of 5.1 compared to 9.5 for the untreated, and DMY was 7% less than the untreateds with seed yield showing a 14% increase.  Data suggests that pendimethalin, dimethenamid-P clethodim, metribuzin, and quinclorac have potential for use in small burnet seed or forage production.

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.

Pre-emergent herbicides are used to control weeds in most of our crops.  Combinations of herbicides are applied to broaden the spectrum of weeds controlled.  Although many studies have been done on the behavior of individual herbicides in the soil, there are few studies that examine the fate of multiple herbicides applied at the same time.  In this study the fate of herbicide combinations (atrazine and metolachlor in corn, flumioxazin and metolachlor in dry beans and pendimethalin and sulfentrazone in sunflowers) in different crops was measured over two years.  The herbicides varied in soil binding and in rates of dissipation.  In sunflowers, pendimethalin remained in the top 7.5 cm of the soil column, whereas sulfentrazone moved rapidly down the profile with heavy irrigation or rainfall.  Flumioxazin also remained in the top 7.5 cm along with metolachlor.  However, flumioxazin rapidly dissipated compared to metolachlor.  In corn, atrazine moved more readily in the soil with a heavy rainfall compared to metolachlor.  Atrazine also rapidly dissipated after the soil temperature increased due to enhanced degradation.  Metolachlor dissipated at similar rates in corn and dry beans.  The fate of each of the herbicides did not appear to be affected by the presence of other herbicides in the same soil.

COMPARISON OF GLYPHOSATE RESISTANT AND CONVENTIONAL ALFALFA CULTIVARS

Steve B. Orloff* and Daniel H. Putnam, University of California, Yreka and Davis, respectively.

Glyphosate-resistant alfalfa was developed in late 1997 and became commercially available in the fall of 2005.  Plantings were subsequently suspended in March of 2007 until a full Environmental Impact Statement (EIS) could be completed.  In January of 2011, USDA again granted non-regulated status to glyphosate-resistant alfalfa.  Growers and the alfalfa industry are interested in the performance of glyphosate-resistant alfalfa cultivars and conventional cultivars under their respective weed management systems.  Twelve glyphosate-resistant alfalfa cultivars and twelve commercial cultivars plus a standard check cultivar (Vernal) were planted on June 7, 2005. The treatments were replicated four times. In the seedling year the conventional varieties were sprayed with imazamox at 0.04 lbs ai/A and the blocks of glyphosate-resistant varieties were treated with glyphosate at 1.0 lb ai/A or imazamox at the same rate used on the conventional varieties. In years 2, 3 and 4 the conventional alfalfa and a block of glyphosate-resistant cultivars were treated with a dormant-season application in mid-March of Velpar at 0.5 lbs ai/A plus paraquat at 1.0 lbs ai/A. In the last year of the stand, the herbicide treatment was changed to metribuzin at 0.5 lbs ai/A plus the paraquat treatment, a typical treatment for the last year of an alfalfa stand to avoid plant-back problems.  The same rate of glyphosate was used each year.  By spraying the glyphosate-resistant cultivars with glyphosate or conventional herbicides in different blocks it was possible to separate alfalfa cultivar performance from crop phytotoxicity. Weeds were completely controlled throughout the trial with all the herbicide treatments so weed biomass did not influence yield. The alfalfa was harvested with a Carter forage harvester two times in the seeding year (2005) and four times per year the following years (2006-2009). Averaged over all 12 glyphosate-tolerant cultivars, the first-year alfalfa yield was 0.30 tons per acre greater when the alfalfa was treated with glyphosate than when treated with imazamox.  In the subsequent 4 years when the alfalfa was treated with winter-dormant herbicides, there was not a consistent difference in yield when the glyphosate-resistant cultivars were treated with glyphosate versus conventional herbicides. However, over the 5-year stand life, alfalfa yield was 0.48 tons greater when the glyphosate-tolerant alfalfa was treated with glyphosate compared with conventional herbicide treatments.  Glyphosate-resistant cultivars and conventional cultivars yielded similarly.  Over the 5 years, the yield of the glyphosate-resistant cultivars was 0.26 tons per acre less than the conventional varieties when treated with the conventional herbicide treatments.  However, the glyphosate-resistant varieties yielded 0.22 tons higher than conventional varieties over the 5 years when treated with glyphosate.  There were significant differences between individual cultivars and there were high yielding conventional and glyphosate-resistant cultivars.  All cultivars yielded higher than Vernal, the check variety.

Summer Annual Weed Control in Established Alfalfa in California

Andre Biscaro, Steve Orloff and Rob Wilson, University of California Cooperative Extension, Lancaster, Yreka and Tulelake, CA, respectively.

As a perennial plant with a long growing season, alfalfa is susceptible to weed invasion by both winter and summer annual weeds. Summer annual weeds, particularly pigweed (Amaranthus spp.), green and yellow foxtail (Setaria spp.) and lambsquarters (Chenopodium album) appear to be an increasing problem in the Intermountain and High Desert areas of California. Two trials were conducted in the Intermountain region of northern California in 2007 and 2008 with the objective of full-season control of both winter and summer annual weeds with a single dormant-season herbicide application. The treatments consisted of the winter-dormant applied herbicides hexazinone, diuron (one study only), metribuzin, and paraquat applied with and without varying rates of pendimethalin.   Any treatment with hexazinone completely controlled the winter weeds shepherd’s purse (Capsella bursa-pastoris) or tansy mustard (Descurainia pinnata). Gramoxone applied alone or tank mixed with pendimethalin did not provide acceptable control of these mustard species. The winter dormant-applied herbicides alone did not adequately control the summer weed spectrum. However, when combined with pendimethalin, foxtail and lambsquarters were controlled. The higher rate of pendimethalin (3.8 lbs/A) was needed for pigweed control and for late-season foxtail control in one trial. In the High Desert of southern California, a single dormant-season application has not been sufficient to control pigweed in mid to late-season cuttings, especially where dairy manure is intensively applied. This area has a longer growing season (7 cuts compared with 3 or 4 in the Intermountain area). A trial was conducted in 2010 to evaluate nine pre-emergent treatments using different rates, combinations and split application of trifluralin, pendimethalin, flumioxazin and prodiamine applied on March 5^th (before the first cut) and on June 2^nd (after second cut), and six post-emergent treatments using different rates and combinations of imazomox, pendimethalin and imazethapyr applied on June 2^nd.  Pigweed control was evaluated three times: after third, fourth and fifth cuts. Overall, the pre-emergent treatments performed significantly better than the post-emergent. A single application of prodiamine applied before first cut provided the best control (averaged 99% for the three evaluations), followed by a split application of pendimethalin (86% control) and a split application of pendimethalin and flumioxazin (83% control). Among the post-emergent treatments, only the tank-mix of imazamox + imazethapyr approached commercially acceptable control at 77% pigweed control.

ABSTRACT

Penoxsulam Herbicide for Weed Control in California Tree Nuts

D.G. Shatley*, R.K. Mann, B. Bisabri, M. Fisher, J.P. Mueller, J.S. Richardson and M. Sorribas

Penoxsulam (Tangent^TM)) is a new broadspectrum tree nut herbicide to be launched in the United States for the control of many winter annual weeds in bearing and non-bearing almonds, walnuts, pistachios and pecans.  Tangent is a 2.0 lb ai/gallon SC (Suspension Concentrate) formulation containing 240 g of penoxsulam per liter.  Tangent provides pre-emergence and post-emergence control of glyphosate resistant and susceptible horseweedl (Conyza canadensis) and fleabane (Conyza bonariensis), as well as the control of many other winter annual weeds including annual sowthistle (Sonchus oleraceus), California burclover (Medicago polymorpha), coast fiddleneck (Amsinckia menziesii var. intermedia), common chickweed (Stellaria media), purple cudweed (Gamochaeta purpurea), cutleaf evening-primose (Oenothera laciniata), henbit (Lamium amplexicaule), mustards (Sinapis and Brassica spp.), pineapple-weed (Matricaria discoidea), prickly lettuce (Lactuca serriola), redmaids (Calandrinia ciliata), shepherd’s-purse (Capsella bursa-pastoris), and willowherb (Epilobium spp.).

Tangent can be used at 1.0 oz/acre (17.5 gr ai/ha) for short term residual control (2 to 3 months) up to 2.0 oz/acre (35 gr ai/ha) for long term residual control (4 to 6 months). Tangent can be tank mixed with other postemergence and residual herbicides labeled for use in tree nuts for broader spectrum control and complete burndown of all existing weeds. Tangent may be applied during the winter dormant period up to March 15^th.  A sequential application of 1 oz maybe applied up to 60 days prior to harvest.

^TM Trademark of Dow AgroSciences LLC

Always read and follow label directions.

Penoxsulam + Oxyfluorfen (Pindar^TM GT) 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 horseweed (Conyza canadensis) and hairy 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 menziesii var. intermedia), common chickweed (Stellaria media), cudweed (Gamochaeta spp.), cutleaf evening-primose (Oenothera laciniata), filaree (Erodium spp.), henbit (Lamium amplexicaule), mallow (Malva spp.), mustards (Sinapis and Brassica spp.), prickly lettuce (Lactuca serriola), redmaids (Calandrinia ciliata), mallow (Hibiscus 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

ABSTRACT

Two Years of Efficacy Comparison with Two Glysortia Glyphosate Formulations and Two Industry Standards.  Jim T. Daniel, Ag Consultant, Keenesburg, CO, and Phillip Westra, Colorado State University, Fort Collins, CO.

Two Glysortia glyphosate formulations, GLYSORT and GLYSORT PLUS, were compared to ROUNDUP POWERMAX, ROUNDUP WEATHERMAX and TOUCHDOWN HIGH TECH in two greenhouse and three field efficacy trials in 2009 and 2010.  Greenhouse evaluations were conducted using corn, dry beans, sunflower, barnyardgrass, velvetleaf, redroot pigweed, green foxtail, kochia, and common lambsquater.  Evaluations included both visual observations and dry weight.  One field study was conducted with kochia in 2009 and two field studies with kochia and prickly lettuce were conducted in 2010.  Visual percent control ratings were taken in all three field studies.

There were no differences in weed control among like glyphosate formulations when averaged across trials and species.  GLYSORT PLUS provided weed control equal to ROUNDUP POWERMAX  (both with 14% surfactants included) but GLYSORT  provided weed control equal to or better than TOUCHDOWN HIGH TECH (7% surfactants included). 

Italian ryegrass (Lolium multiflorum) is one of the most widespread and difficult-to-control weeds in winter wheat production in Oklahoma.  In recent years, Oklahoma winter wheat producers have been noticing a lack of control of Italian ryegrass with ALS inhibitor herbicides where they previously had satisfactory control.  To address the issue of potential herbicide-resistance, seed samples from 300 Italian ryegrass populations were collected from winter wheat fields in Oklahoma in 2008 and 2009 and screened in the field for resistance with nine herbicides (chlorsulfuron + metsulfuron, mesosulfuron, pyroxsulam, imazamox, flufenacet + metribuzin, diclofop-methyl, pinoxaden, quizalofop P-ethyl, clethodim, and glyphosate) representing five modes of action (ALS inhibitor, shoot growth inhibitor + PSII inhibitor, ACCase inhibitor, and aromatic amino acid synthesis inhibitor).  Standard field use rates for each herbicide were used.  Visual estimates of weed control were collected and populations were characterized as “susceptible” (80-100% control), “suppressed” (51-79% control), or “resistant” (≤50% control).  In 2008 and 2009, though control varied among individual herbicides, only 28-51% of the populations tested were classified as controlled with ALS inhibitor herbicides, indicating that ALS-resistant Italian ryegrass is prevalent throughout Oklahoma.   All ryegrass populations collected in 2008 and 2009 were susceptible to flufenacet + metribuzin, quizalofop P-ethyl, clethodim, and glyphosate.  Though ACCase-resistant Italian ryegrass is not thought to be present in Oklahoma, three populations collected in 2009 were controlled at less than 50% with diclofop-methyl and pinoxaden.  Herbicide-resistance testing efforts will continue to monitor the development and spread of ACCase- and glyphosate-resistant Italian ryegrass.

A study was conducted in 2010 to evaluate the use of desiccants as a canola harvest aid. The objectives were to determine the effect of desiccants applied preharvest on canola yield, seed moisture, and seed quality. The desiccation treatments were applied when at least 60% of the seeds had started to turn color.  Treatments included saflufenacil at 1, 2 and 4 fl oz; glyphosate at 0.75 lb ae; saflufenacil plus glyphosate (1 fl oz + 0.75 lb ae); diquat at 1.5 pt; and flumioxazin at 1 oz ai.  A swathed treatment and straight cut-only treatment were also included.  Diquat was applied at 20 gpa.  All other desiccation treatments were applied at 10 gpa. Treatments were evaluated for percent pod and stem desiccation at 4, 8, 11, and 14 days after treatment (DAT).  Seed moisture at harvest was estimated using a hand-held moisture tester.  Yield and test weight were determined by harvesting the middle four feet of each plot with a small plot combine.  Seed samples were evaluated for green count, damage, and overall grade. Diquat provided faster visual pod and stem desiccation throughout the study.  Glyphosate alone was slower compared to other treatments; however, there was some maturity variability between reps. Treatments containing glyphosate tended to have lower canola yield; however, we do not know if this is a true treatment effect or just due to natural plot variability.  The swathed treatment yielded slightly higher than desiccated treatments, which is in contrast to previous studies.  Test weight was not impacted by any of the desiccants.  Test weight for the straight cut treatment was slightly lower, which may be due to harvesting at slightly higher seed moisture. Green count was higher in the diquat and swathed treatments compared to the other desiccants and the straight-cut treatment.  In a 3-year desiccation study from 2005-2007, we did not observe yield reductions from diquat or paraquat treatments compared to swathing.  This study will be conducted again in 2011 to help answer these questions.

Field trials were conducted in 2009 and 2010 at the NDSU Carrington Research Extension Center to evaluate early-season weed control and soybean response to soil-applied saflufenacil. Experimental design was a randomized complete block with three replicates. The reduced-till, dryland trials were conducted on Heimdal-Emrick loam soil with 5.9 pH and 3.9 to 4.2% organic matter. Dairyland Seed RR ‘0401’ inoculated soybean was direct-seeded in standing small grain stubble in 30-inch rows on May 21 (2009) and May 19 (2010). Preplant (2009) or PRE (2010) burn-down herbicides were applied to annual broadleaf weeds ranging from 0.5- to 2-inches tall. Rainfall ranging from 0.9 to 1.1 inches occurred within 4 to 9 d after treatment (DAT). Herbicide treatments included glyphosate at 0.75 lb ae/A, saflufenacil at 0.023 lb ai/A plus glyphosate at 0.75 lb ae/A, and saflufenacil at 0.023 lb ai/A plus imazethapyr&glyphosate at 0.048&0.56 lb ae/A (2010). POST glyphosate at 0.75 lb ae/A was applied during early July across the trial except the untreated check. Soybean was harvested with a plot combine during the first half of October.  In 2009, kochia control 4 DAT was 40% with glyphosate compared to saflufenacil plus glyphosate at 86%. However, 13 and 27 DAT, kochia control was similar between glyphosate and saflufencil plus glyphosate (96 to 98% and 83 to 89%, respectively). Kochia control declined to 50% with glyphosate 47 DAT compared to control at 72% with saflufenacil plus glyphosate. In 2010, common lambsquarters control 19 DAT was 77% with glyphosate compared to saflufenacil treatments at 87 to 91%. At 42 DAT, common lambsquarters control was 91% with saflufenacil plus imazethapyr&glyphosate. Wild buckwheat control at 7 and 19 DAT with glyphosate was 75 to 77% compared to 86 to 94% with saflufenacil treatments. No crop response was observed during either trial. Soybean seed yield was similar among treatments in 2009. In 2010, soybean yield increased with herbicides compared to the untreated check. During both years, yield tended to be highest with saflufenacil treatments. [58]

The 2010 Sharpen label prohibits tank mixing saflufenacil with other PPO inhibitors such as sulfentrazone and flumioxazin.  Previous NDSU and MSU research has shown that these combinations may provide better weed control than either herbicide applied alone.  This study was conducted at Minot, ND and Bozeman, MT to confirm whether a tank mix of two PPO inhibitors is safe on dry pea and chickpea.  All treatments were applied preemergence (PRE).  Treatments included saflufenacil (25 g/ha), sulfentrazone (158 g/ha), fomesafen (210 g/ha), flumioxazin (72 g/ha), and pendimethalin (1,600 g/ha).  Saflufenacil (25 g/ha) was also tank mixed with each of the other herbicides.  Glyphosate was applied PRE across the entire study.  The studies were conducted using traditional small plot techniques.  At Minot, flumioxazin was the only treatment that caused significant dry pea or chickpea injury (≤15%).  Tank mixing saflufenacil with flumioxazin did not significantly increase injury in either crop.  There was essentially no injury from saflufenacil alone or tank mixed with other PPO inhibitors such as sulfentrazone and fomesafen.  In chickpea, saflufenacil and sulfentrazone applied alone provided about 80% biennial wormwood control.  Applied together as a tank mix, saflufenacil + sulfentrazone provided 99% biennial wormwood control.  Similar increases were observed with saflufenacil + fomesafen and saflufenacil + flumioxazin.  At Bozeman, the study was conducted in dry pea only.  No crop injury was observed.  All treatments provided good to excellent control of a light population of Russian thistle, kochia, prickly lettuce, wild mustard, and wild buckwheat.  Previous MSU trials have shown an advantage in weed control when two PPO herbicides are combined as PRE treatments in a pea crop. 

Various studies have provided estimates of seed counts for a variety of weeds  Studies have estimated “one Ipomoea purpurea (PHBPU) can produce 26,000 seeds/plant and another study reported Anoda cristata (ANVCR) produced up to 17,832 seeds/plant.    Numerous biotic and abiotic factors contribute to the quality and quantity of seeds produced by an individual plant as well as the germinability of the seed once it has matured. A trial was conducted over the summer of 2009 to  determine the effect of Meloidogyne incognita (RKN) on seed production and germinability of three annual weeds common in crop production in southern New Mexico:  ANVCR, PHPBU Physalis wrightii (PHYWR).  The study was established in 76-cm- diameter microplots containing fine sandy loam in a completely randomized paired split plot design.  Seven pairs of plots were planted with one species to establish three plants for each plot; each pair of micoroplots consisted of one RKN inoculated (+RKN) plot and one non-inoculated (-RKN) plot for each species for a total of 42 plots.  Growing degree hours were calculated for seed emergence, flowering, seed set and harvest dates.  Seeds were harvested and dried; 100 seeds/species were counted and weighed to estimated total number of seeds/plot.  One hundred seeds/ species were planted and counted as they germinated.  Separate analysis for each species was performed using SAS GLM and GENMOD.  The analysis of growing degree days from emergence to seed production was not statistically different for +RKN or  -RKN.  Total estimated seed production (dry seed weight) was not significantly different within each species.  The analysis of seed germination by species and RKN treatment was statistically different for ANVCR with a trend of fewer seed germinating from plants that had grown in the presence of RKN.  In the analysis for PHYWR fewer seeds germinated from the plants grown in the absence of RKN than in the presence of RKN, but the difference was not statistically different.  PHPBU germination was statistically different for the RKN treatments with fewer seeds germinating from the plants grown in the presence of RKN.

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.

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 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”.

Weed Prevention Areas (WPAs) are a relatively new tool developed to help slow the spread of weeds into non-infested areas, and minimize environmental and economic costs.  They are defined as cooperatively managed areas that focus on implementing weed prevention and early detection at a community level.  A guide was designed to provide interested groups a step-by-step process for effectively implementing a prevention program in their area.  The process includes five main steps 1) introduce the WPA concept, 2) organize the WPA, 3) develop the action plan, 4) implement the action plan, and 5) evaluate the action plan.  For each step the guide contains information, explanations, and ideas providing guidance while remaining flexible enough that a WPA can be developed to fit different situations and needs.  At the end of each step, an additional resources page provides links and references to ensure that interested groups have the necessary information and tools to succeed.  Several worksheets and templates are also included for use in planning and recording management activities.  This guide will assist landowners in developing proactive, coordinated management efforts to protect valuable resources from the costly, damaging effects of invasive weeds.

The State of Utah has listed 27 plants on their noxious weed list.  An Extension Publication titled “Noxious Weed Field Guide for Utah” has been used extensively to teach the public about the identification and biology of the legally listed noxious weeds.  More than 25,000 copies of the Noxious Weed Field Guide for Utah have been sold during a 10-year period.  Utah State University County Agents, County Weed Supervisors, and members of the Utah Nursery and Landscape Association requested a weed identification guidebook that was smaller than “Weeds of the West” but more expansive than the Noxious Weed Field Guide.  In addition, many horticulturalists said that they had problems with commonly occurring weeds that are not on the noxious weed list and thus would like a weed identification guide that included noxious weeds (as appropriate) but focused on weeds more commonly encountered in the yard and garden.  The concept of a guidebook to be titled “Common Weeds of the Yard and Garden” was developed in the summer of 2005.  A graduate student was recruited for the project in 2006 and support from external sources such as County Agents, Weed Supervisors, and horticulturalists was solicited.  The advisory committee limited the publication to 50 weeds.  Text was written and images were collected during 2007 and 2008.  Guidebook layout considerations included  listing weeds alphabetically by common names; categorizing weeds according to problem area, such as weeds of turf, weeds of gravel driveways, weeds of gardens and weeds of flower beds; organizing by appearance (color, type of inflorescence, prostrate, woody, etc); and, listing weeds from most detrimental to least. Ultimately weeds were organized alphabetically by scientific family name, and within families by scientific generic and specific names.  Fourteen references were used throughout the guidebook.  The objective was to have all information in the guidebook corroborated by at least two credible sources.  An internet-accessible version was developed in 2007. The expanded version of the guide (web version) was completed by summer 2009. The shorter booklet version was completed by fall 2009.  The guidebook was completed and 5000 copies were printed in February 2011.  Online access of the expanded version of the guidebook is found at extension.usu.edu/weedguides.  Of the 50 weeds listed in the “Common Weeds of the Yard and Garden” guidebook only five are also listed on the state noxious weed list for Utah.

Locoweeds are plants of the Fabaceae family that can be highly poisonous to livestock and wild animals.  Locoweed toxicity depends on the association of a plant and a fungal endophyte which produces the alkaloid swainsonine (SWA); however, environmental factors affecting SWA synthesis are unknown.  Additionally, locoweeds can be associated with a bacterial symbiont, nitrogen-fixing Rhizobium spp. that provides reduced nitrogen for plant growth and may alter SWA synthesis.  We examined responses of SWA production, photosynthetic activity, pigment levels, and plant growth to nitrogen (N) supplementation in four locoweed taxa which differ in average leaf SWA concentration.  Plants were grown in a greenhouse environment and provided 0 to 4 mM of ammonium nitrate; leaves were collected several times over a three-month period and analyzed for SWA.  Shoot and root mass, leaf photosynthetic rate, and pigment concentrations had positive N dose responses and supplemental N increased shoot growth more than root growth in all four locoweeds.  A small, temporary increase of SWA with increasing N was detected only in the very low SWA producer (0.001 % SWA in leaves) Astragalus mollissimus var. matthewsii.  SWA levels in moderately high producers (0.15-0.20 % SWA) Oxytropis sericea and A. m. var. bigelovii had negative dose response to supplemental N, while the highest SWA producer (0.35 % SWA) A. m. var. mollissimus did not have a significant response.  Our results demonstrate that nitrogen supplementation, even at levels which promote locoweed growth and photosynthesis, does not have a consistent effect on SWA production.

Weed seed germination patterns and soil seed bank depletion are strongly influenced by seed dormancy which is inextricably tied to the age structure of weed seed banks. No method currently exists to quantify weed seed bank age structure in situ.  Once seed is shed from the maternal plant to the soil, there is no way to differentiate that seed from others already in the soil. The objective of this project was to develop a method for using stable carbon isotopes as tracers so we may better study the impact of land management practices on weed seed banks. Maternal jointed goatgrass plants were tagged under greenhouse and field conditions with a carbon isotope signature, and that signature was passed on to the seed that was produced.  δ¹³C values for jointed goatgrass seed produced under ambient CO₂ conditions averaged -26.4, with a 99% confidence interval of -25.4 to -27.4.  When maternal plants were exposed to 99-atom % ¹³CO2 for 2 hours during seed production, δ¹³C values increased to 15.9 on average, with 99% confidence interval of ‑5.6 to 37.4.  Due to these differences, plants exposed to a single pulse of ¹³CO2 produced seed that was easily and reliably traceable.  By analyzing the soil seed bank for the carbon isotope signature in subsequent years, we will be able to monitor the dormancy, viability, and emergence patterns under normal agricultural practices without the need for soil sterilization or artificial seed bank supplementation.  This line of research may lead to a new understanding of how weed and crop management practices influence weed seed bank dynamics. 

Aminocyclopyrachlor is a new herbicide proposed to control weeds in nonagricultural areas. Absorption and translocation were evaluated on quaking aspen (Populus tremuloides) and black cherry (Prunus serotina). Three formulations were studied using two application methods. The acid (DPX-MAT28) was applied foliarly. Two formulations were applied basally; an oil soluble liquid of the acid (DPX-MAT28OL) and an emulsifiable concentrate of the ester (DPX-KJM44EC). For foliar treatment, the second leaf on the lowest branch was covered and plants were treated with a non-radiolabeled mixture containing 210 g ai/ha DPX-MAT28 and nonionic surfactant at 0.25% v/v. Covered leaves were treated with 29.29 kBq radioactive herbicide. For basal applications stems were spotted with 10 µL of herbicide mixture containing non-radiolabeled (0.25 mg ai), radiolabeled material (22.56 kBq) and bark oil. Plants were harvested at 2, 8, 24, or 72 hours after treatment (HAT) and divided into parts. Parts were dried, weighed, ground and sub-sampled for oxidation and ¹⁴C recovery. Foliar-applied DPX-MAT28 reached a maximum absorption of 9.9% in aspen and 8.0% in cherry. Translocation of applied radiolabeled herbicide was 2.0% and 1.2% at 72 HAT. Basal-applied DPX-MAT28OL absorption was 48.3% in aspen and 67.7% in cherry at 72 HAT. Translocation 72 HAT was 13.0% in aspen and 20.2% in cherry. Basal application of DPX-KJM44EC had absorption of 54.8% in aspen and 53.0% in cherry at 72HAT. Translocation was 24.0% in aspen and 15.8% in cherry 72 HAT. Woody plants may be better controlled using basal bark herbicide application when compared to foliar application.

Sulfonylureas and imidazilinones are important classes of herbicides used to control many broadleaf weeds including prickly lettuce (Lactuca serriola) in small grain production systems in the inland Pacific Northwest. Over the last two decades, prickly lettuce has developed resistance to several acetolactate synthase (ALS) inhibitors in two chemistry classes. To begin to understand the possible mechanisms of resistance present in ALS in prickly lettuce, six known ALS-resistant biotypes of prickly lettuce from the inland Pacific Northwest were screened for resistance to 13 ALS-inhibitors in the four chemistry classes . The study was conducted with a randomized complete block design with split plots and four replications. The herbicide treatments were main plots, and the biotypes were sub-plots. The study was repeated in space. At the 4 to 6 leaf stage, individual treatments containing all six biotypes were sprayed with imazapic, imazapyr, imazethapyr, flucarbazone, propoxycarbazone, chlorsulfuron, iodosulfuron, metsulfuron, prosulfuron, thifensulfuron, triasulfuron, tribenuron, and pyroxsulam at maximum labeled rates. For comparison purposes, a non-treated check was included. Visual estimates of control were recorded 20 days after treatment. Aboveground biomass was harvested after rating. Both fresh and dry weights were recorded. The six prickly lettuce biotypes were resistant to most of the ALS-inhibiting herbicides used. While the majority of the selected herbicides were not effective at controlling these prickly lettuce biotypes, control was observed when imazapyr, triasulfuron, and prosulfuron were applied at labeled rates in several biotypes. Some biotypes were resistant to a greater number of the herbicides than others suggesting variation of binding efficiency to ALS within herbicide chemical subclasses, increased herbicide metabolism, or variation in mutations in the binding site. Prickly lettuce is a highly variable weed species that displays herbicide resistance to a wide range of ALS inhibiting herbicides.

In Oregon’s Willamette Valley, a combination of need for broadleaf rotational crops and an increased desire for local biofuel production has created interest among growers for planting Brassica napus (canola). However, questions have arisen over the potential damage large scale canola production could have on the existing Brassica vegetable seed production industry. The reputation of the Brassica vegetable seed production industry is based on the purity and the high quality of seed. In fact, a seed lot may be rejected if more than three outcrossed seed per 1,000 seed is found. The risk is even greater if the crops are cross pollinated with transgenic canola because some international purchasers of the vegetable seed crops have zero tolerance for transgenic contamination. While there is a great deal of information on hybridization between canola and weedy species, very few studies address hybridization between canola and related vegetable species. To address this issue, experiments were conducted in 2007, 2008, and 2009 using Brassica rapa and Brassica oleracea inbred lines as pollen receptors placed within a conventional (non GMO) B. napus field. Flow cytometry, morphological analysis, and molecular markers were used to identify hybridization between the species. Greenhouse crosses were conducted using either a conventionally produced imazamox resistant or a transgenic glyphosate resistant B. napus line as the pollen parent and either a self incompatible B. rapa var. chinensis (Chinese cabbage) or cytoplasmic male sterile (CMS) B. oleracea var. italica (broccoli) inbred lines as the maternal parent. Herbicide resistant B. napus lines were used because they provide a reliable selectable marker for positive identification of a cross. Results of the field experiments indicated that hybridization occurred 74% in 2007, 89% in 2008, and 15% in 2009 between B. napus and B. rapa inbred lines. However, no hybridization occurred between B. napus and either B. oleracea inbred line. Results of the greenhouse crossing experiments using B. rapa as the maternal parent resulted in hybridization rates which ranged from 0 to 15.3% depending on B. rapa var. chinensis inbred line, and on which herbicide resistant B. napus paternal parent was used in the cross. Greenhouse crosses using B. oleracea inbreds as the maternal parent produced no germinable seed, and none of the aborted seed tested positive for the presence of the transgene. Presence of transgenic material was detected in both germinable and non-germinable seed produced on non-transgenic B. rapa female plants in the greenhouse crosses. We believe this is the first documentation of transgenic material identification in non-germinable seed produced on non-transgenic plants.  This research demonstrates that the potential exists for hybridization between canola and some Brassica vegetable species under field conditions.

Land managers must set weed management priorities if limited resources are to be utilized effectively.  Weed surveys/inventories assist land managers in this process by providing information regarding the identity, location, and relative abundance of weeds on their land.  Although this information is vital, it can be challenging to select an approach that provides the necessary data to meet management objectives while remaining efficient and cost effective.  This paper critically evaluates four wildland weed mapping methods.  These methods were defined as:  1) paper-drawn:  patch size and shape depicted by hand drawing on a topographic map, 2) buffered point: each patch is assigned to a patch size category and recorded as a single GPS point 3) screen-drawn: patch size and shape estimated and drawn to scale on a DRG topographic map displayed on a GPS screen, and 4) perimeter-walked:  patch perimeter walked while GPS unit continuously collects position points at one second intervals.  Six experienced weed mappers independently recorded the location and size of eight sagebrush patches using each method.  Time and accuracy were evaluated for each method based upon mapping time, distance walked, horizontal precision error, estimated size error, and shape error.  The paper-drawn method was significantly less accurate than other methods at recording patch size and location.  There was no significant difference in the accuracy of the buffered point, screen-drawn, and perimeter-walked methods at reporting patch size and location.  The need to cover land area quickly and efficiently favors the selection of the buffered point or screen-drawn method due to time and distance factors.  However, if patch shape is an important factor, the perimeter-walked or buffered point may be the best choice of methods tested.  Overall, the accuracy of any data collected is dependent upon the proficiency of the weed mapper in using the selected method.

Modeling Spatial Patterns for Rush Skeletonweed Dispersal in the Salmon River Canyon

Sandya R. Kesoju, B. Shafii, T.S. Prather,  L.W. Lass, and W.J. Price, University of Idaho, Moscow, ID.  

Abstract

Rush Skeletonweed (Chondrilla juncea L.) is a perennial Asteraceae that infests well-drained, light textured soils commonly found in the mountain foothills and canyon grasslands of the Pacific Northwest. Approximately 1.2 million ha are infested in Idaho with dispersal into Montana. Spatial network models based on likelihood of occurrence are being used to model dispersal. Overall, our research focuses to produce dispersal models for use in making land management decisions at a landscape scale. One part of the effort includes assessing spatial dependence of rush skeletonweed dispersal and relate those to the role of wind speed and wind direction in determining the potential patterns of dispersal. A study area including the Salmon River Canyon, Idaho was used for modeling spatial patterns of rush skeletonweed dispersal. The area was divided into five subunits for the purpose of modeling the presence or absence of rush skeletonweed. In each subunit, geostatistical modeling techniques were used to provide insight into the spatial patterns of rush skeletonweed. These models provide useful information for modeling rush skeletonweed dispersal. After obtaining an empirical semivariogram, a theoretical semivariogram model was estimated for each subunit. Subunit models indicated different azimuth orientations and infestation patterns within the river canyons. Model forms encompassed spherical, Gaussian, exponential and wave-effect models. Spatial dependence distance ranged from 2 km to 5 km and demonstrated an anisotropic pattern from 0 to 45 degrees. The results indicate a strong effect of canyon orientation and are likely due to local wind patterns within the canyon grasslands. Results provide justification for a large scale effort to create a wind GIS layer that will be used within a network model for the purpose of identifying direction and relative force for movement within grasslands and foothills of Idaho and western Montana.

Common tansy (<i>Tanacetum vulgare L.</i>) was first introduced to the United States from Europe in the 1600s.  Cultivation for traditional folk medicines and other domestic uses accelerated its spread throughout temperate regions of North America.  Common tansy is currently listed as a noxious weed in four western states.  The plant contains alkaloids that can be toxic to humans and livestock if consumed in large quantities.  Sites susceptible to invasion include roadsides, fence rows, irrigated pastures, and ditch or stream banks.  The plant often occurs in association with other noxious weeds such as Canada thistle (<i>Cirsum arvense</i>) or knapweeds (<i>Centaurea</i> sp.). 

Field trials were established at two locations in Missoula, MT in June 2006 and 2008 to determine effectiveness of various herbicide treatments on common tansy.   Sites included either common tansy alone or in a complex with spotted knapweed (<i>C. stobe</i>).  Herbicide treatments were applied with a CO₂ backpack sprayer at 13.5 gpa in a randomized complete block design with three replications per treatment.  Aminopyralid was applied alone at 1.25 and 1.75 oz ae/A (Milestone^® at 5 and 7 fl oz/A) , aminopyralid plus 2,4-D at 1.75 oz ae/A + 14 oz ae/A (ForeFront^® R&P at 2.6 pts/A), aminopyralid plus metsulfuron at 0.8 + 0.14, 1.3 + 0.24, 1.71 + .31 oz ae/A (Chaparral™ at 1.5, 2.5 and 3.3 oz product/A), and metsulfuron alone at 0.3 oz ae/A.  Plots were visually evaluated for percent control 12 and 27 months after treatment (MAT).   

Aminopyralid plus metsulfuron at all rates provided greater than 95% common tansy control 12 MAT.  This level of control was maintained for 27 MAT with rates used in this study that were greater than 0.8+0.14 oz ae/A.  Control with aminopyralid plus metsulfuron was similar to metsulfuron alone at 0.3 oz ae/A.  Aminopyralid alone and aminopyralid plus 2,4-D did not provide acceptable common tansy control either 12 or 27 months after treatment. Aminopyralid plus metsulfuron (Chaparral) was the only herbicide treatment that provided excellent control (>95%) of both spotted knapweed and common tansy.  On sites having a complex of weeds such as common tansy, spotted knapweed, and Canada thistle, aminopyralid plus metsulfuron at rates of 1.3 + 0.24 oz ae/A (Chaparral at 2.5 oz product/A) and above provided superior control of the weed complex compared to either metsulfuron or aminopyralid alone. 

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Aminopyralid and clopyralid are broadleaf herbicides that are less likely to adversely affect desirable plants than other herbicides with similar use site registrations.  This makes them potentially suitable for invasive weed control on rangeland and wildland sites where conservation of native species is an objective.   An experiment was established in north central Idaho to determine relative effectiveness of two rates of aminopyralid and one rate of clopyralid applied in fall, for control of invasive species and to determine  effects on native plant species and plant community structure. 

Early fall application was chosen in part to test the ability of aminopyralid to suppress late fall germination of annual grasses, which has been observed in other trials in the western U.S.  Herbicide treatments applied were aminopyralid at 0.047 and 0.078 ai/A (Milestone^® at 3 and 5 oz per acre) and clopyralid at 4 oz ai/A (Transline^® at 11 oz per acre), and no herbicide.    Field experiments were designed as randomized complete blocks with five replications and initiated in 2009.   Pre-treatment sampling was conducted in early July 2009, and the first year post-application vegetation sampling was conducted in early July of 2010.  Broadcast ground applications were made with a CO₂ backpack sprayer in September of 2009.   Data collection included canopy cover in 36, 0.25m² microplots within each of twenty macroplots.  Within each microplot nested rooted frequency was also assessed for weeds of interest.  There were a total of 38 species present on the site at initiation of the experiment in 2009 and 50 in 2010. Exotic annual grasses and forbs dominated the site, but remnants of native grasses (bluebunch wheatgrass) occurred as well as native biscuitroots, lupine, milkvetch, and other natives.  

Evaluations of herbicide effects were based on changes in canopy cover compared to non-treated controls.  Pretreatment canopy cover data was used as a covariate.   Differences (as the estimated marginal means) between treatments and treatment and control indicated that yellow starthistle, thymeleaf sandwort, black medic lentil vetch, and winter (hairy) vetch were readily controlled (>90 percent) by all of the treatments.  Other exotic forbs increased in cover, sometimes significantly for a specific herbicide: small geranium, Dalmatian toadflax, common St Johnswort, and some exotic forbs were little changed (chicory).

Aminopyralid at 0.078 oz ai/A (5 oz/A) reduced field brome and medusahead (40 to 50 % canopy cover ), but had little effect on downy brome.  Downy brome germination appeared to occur before spraying as early as August,  and continued throughout spring.  Ventenata dubia increased regardless of rate of aminopyralid or clopyralid applied.  Of the native forbs observed or tested;, common yarrow, two biscuitroots, silky lupine, grassy tarweed, Douglas knotweed, and Menzies’ fiddleneck canopy cover did not change during course of the experiments.  Bluebunch wheatgrass increased in plots where aminopyralid at 0.078 oz ai/A (5 oz/A) was applied.  The relative cover and dominance of native species increased over the course of the experiment, due both to increased native annual forbs and bluebunch wheatgrass. Some non-susceptible exotic forbs (Dalmatian toadflax and common St. Johnswort) and grasses (Ventenata) increased in cover and frequency on herbicide-treated plots. Response of these undesirable species to treatments in these experiments highlights that the essential first step of developing a vegetation management strategy is to determine plant community structure.  With this community information, selection of best practices and sequence and combination in which they should be applied can be determined to best meet land management objectives.   Additional sampling is planned in 2011 to determine to further understand the long-term response of plant populations to herbicide treatments. 

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Aminopyralid was designated as a reduced risk pesticide compared to other registered herbicides by the US EPA during registration.  Aminopyralid (Milestone^®) is a desirable alternative to other herbicides for broadleaf invasive weed control on rangeland and wildland sites.  Effects of aminopyralid on desirable native forbs and shrubs are a consideration for land managers when making decisions about controlling invasive plants.  Many land managers have made the assumption that applying aminopyralid in the fall to dormant forb species would provide better tolerance than would summer applications.  The purpose of this research was to determine the effect of date of aminopyralid application on forb tolerance.  Experiments were established on diverse native plant communities near Missoula, Montana; Steamboat Springs, Colorado; Ortonville, Minnesota; and Big Stone, South Dakota.  Field experiments were designed as randomized complete blocks with four to eight replications and initiated in 2008 or 2009.  Herbicide treatments were aminopyralid at 0, 1.25 or 1.75 oz ae/A.  Broadcast ground applications were made in June, July, and October with CO₂ backpack or bicycle sprayers.  Data collected across sites varied from either canopy cover or plant counts along permanent transects, or plant density within each plot.  First year post-application vegetation sampling was conducted in June and July the summer after treatment at all locations.  Tolerance to aminopyralid were established for 20 native forb species at the different application dates.   Evaluations were based on individual species reduction in canopy cover or density compared to non-treated controls or baseline density counts data. Four tolerance categories were used:  susceptible (S - 75% or more reduction in canopy cover or density), moderately susceptible (MS - 75 to 50% reduction), moderately tolerant (MT- 49 to 16% reduction) and tolerant (T – 15% or less reduction).   Of the 20 forb species categorized, tolerance ratings of 12 species were not different regardless of application date.  Species with greater tolerance to aminopyralid following a summer application compared to autumn application were stiff sunflower, Canada goldenrod, stiff goldenrod, and purple prairie clover.  Species more tolerant to an October application of aminopyralid were subalpine buckwheat, lupine, little sunflower, and white prairie aster.  Based on these results tolerance of forb species to aminopyralid may vary depending on application date.  Previous research has shown that most native forbs and shrubs were moderately tolerant to tolerant, or recovered following treatment with aminopyralid applied at various application date. Understanding desirable forb species tolerance to aminopyralid is useful when determining how to utilize this herbicide into invasive plant management programs.

Invasive plants often interfere with and displace desirable plant populations making site re-vegetation necessary to return desirable plant species to acceptable levels. Aminopyralid has great utility to control invasive broadleaf plants in natural areas and wildlands, It is critical that land managers understand how aminopyralid is best used to control invasive plants and facilitate establishment of desirable grass species. The current label for aminopyralid-containing products allows for its use on established desirable grasses or it can be applied in the spring before a fall grass planting. The objective of this research was to determine if grasses can be planted either as a dormant seeding or in the spring following an autumn herbicide application.  Research was conducted at; University of Minnesota, North Dakota State University, and South Dakota State University research farms. Experiments were designed as randomized complete blocks with four replications per treatment combination.  Pre-plant herbicide treatments were applied on September 15, 16, and 22, 2009 at the ND, MN, and SD locations respectively. Treatments included aminopyralid at 0.75, 1.75, and 3.5 oz ai/A (2 times the maximum registered use rate), clopyralid at 6 oz ai/A, and picloram at 8 oz ai/A.  Grasses planted in these experiments were cool season grasses (intermediate wheatgrass, Canada wildrye, and green needlegrass) and warm season grass (big bluestem, little bluestem, sideoats grama, switchgrass, and indiangrass). The SD location included 2 planting times, November 9, 2009 and April 4, 2010,  grasses were planted in ND on April 22, 2010 and in MN on November 17, 2009.  The non-treated checks were hand weeded for most of the early season.  Plant count (number of plants per 0.5 meter of row) and frequency of occurrence (%)were measured in July 2010 at all sites. The planting date main effect was significant (P<0.05) for grass counts and frequency of occurrence. The herbicide by planting interaction for counts of big bluestem planted in the spring was the only significant (P<0.05) interaction. Averaged across herbicide treatment and grass species (except big bluestem) the average grass count from fall plantings was 2.5 plants per 0.5 meter row compared to 5.0 plants per 0.5 meter row for spring plantings. There were no differences across herbicide treatments for fall-planted grasses for either cool or warm season grasses. For the spring planting, the combined warm-season grasses (except big bluestem) showed a trend for a greater number of plants in herbicide-treated plots compared to non-treated areas. Cool-season grass counts in spring plantings in aminopyralid-treated plots ranged from, 7.2 to 7.6 plants per 0.5 meter row compared to clopyralid at 6 oz ai/A and 8 oz ai/A of picloram at 6.6 and 5.2 plants per 0.5 meter row respectively and 5.4 in non-treated plots. There was a trend for counts of warm-season grasses to be less in plots treated with aminopyralid at 3.5 oz ai/A, clopyralid, and picloram (mean of 3.7, 4.2, and 3.2 plants per 0.5 m of row, respectively) when compared to 5.7 plants per 0.5 m of row in plots treated with 1.75 oz ai/A aminopyralid and higher than the 2.2 plants in non-treated plots. Based on these results aminopyralid (Milestone^® herbicide) can be applied in the autumn and several cool- and warm-season grasses planted either as a dormant seeding during the autumn/winter or in the spring will successfully establish if environmental conditions are favorable.  This demonstrates another important utility of Milestone, which is to control invasive broadleaf plants and facilitate revegetation of desirable grasses on sites where remnant populations of desirable grasses are insufficient to recover after invasive plant control.  These data are corroborated by other field experiments conducted in the western US and confirm Milestone fit in rangeland grass revegetation programs.

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

Aphthona spp. flea beetles have reduced leafy spurge throughout North Dakota and native plant species diversity was expected to increase.  However, the reestablishment of native plant species has been slow in areas where the beetles have reduced the weed compared to when herbicides were applied.  A bioassay was conducted in 2004 and 2010 to evaluate the establishment of native grass species in soil taken from Aphthona spp. release and nearby non-release sites.  The native grass species included green needlegrass [Nassella viridula (Trin.) Barkworth], little bluestem [Schizachyrium scoparium (Michx.) Nash], switchgrass (Panicum virgatum L.), and western wheatgrass [Elymus smithii (Rydb.) Gould].  Soil was collected near Medora, ND in 2004 and again in 2010 along with five other locations throughout the state.  In 2004, native grass production was reduced nearly 50% when grown in soil from Aphthona spp. release sites compared to non-release sites.  The greatest reduction occurred with switchgrass, which was reduced 66% compared to plants grown in soil from non-release sites.  Leafy spurge was present at insect-release and non-release sites, suggesting slow native species reestablishment may not be caused by leafy spurge.  The 2010 study is still in progress, but results to date do not confirm the results from the 2004 study as grasses grew equally in soil from release and non-release sites.  The slow recovery of native grass species is unknown and may be due to a chemical inhibition found within the soil not yet identified. 

Yellow toadflax (Linaria vulgaris Mill.) is an exotic perennial forb that  is a serious weed in the Intermountain West and its range is expanding.  It is a difficult plant to control and site to site variation has been dramatic.  Identical herbicide trials were conducted at 5 geographically separated field sites in Colorado.  Chlorsulfuron and imazapyr were each applied at 4 rates.  Field trials were supported by a common garden study and an observational study of root bud phenology.  Biomass from the field sites was analyzed by ANOVA.  Chlorsulfuron applied at 94 g ai/ha controlled > 86% of yellow toadflax at 3 sites and <73% at 2 sites.  Imazapyr applied at 380 g ai/ha controlled > 92% of yellow toadflax at 3 sites, and 53 and 5% at 2 sites.  To better explain the site variation, GR₅₀ values for biomass were calculated and subjected to a correlation matrix with site characteristics.  The correlation matrix revealed that sites at higher elevation and sites with fewer shoots flowering at the time of application required less herbicide for acceptable control. Lower elevation sites and sites with more shoots flowering at the time of application required more herbicide for acceptable control.  The common garden study indicates genetic differences among sites; however, no tolerance or resistance was observed.   The observational study of root bud phenology suggests that applications which occur during a more progressed growth stage provide better control.  Through these studies, a better understanding of the source of variation has been determined and managers can use timing of application to achieve better control of yellow toadflax.

The paper describes the challenges and opportunities for invasive plant management in British Columbia. BC is biologically, culturally and economically diverse, encompassing 14 distinct climatic zones across 365,000 sq mi, roughly the combined area of Washington, Idaho, Oregon, and 85% of California. 94% of the land in BC is public, placing significant responsibility on the provincial government to fulfill the provincial invasive plant management mandates.  BC shares 7 jurisdictional borders with states, provinces, and territories, has over 15,535 mi of rugged coastline, and has the second-largest parks system in Canada. Floristically, BC yields almost 1600 native vascular plant species, 27% considered species at risk. The vastness and diversity that define BC requires a complex, cross-jurisdictional network of community-based collaborations to plan and deliver all aspects of invasive plant management. The Inter-Ministry Invasive Species Working Group coordinates the six million dollars spent on invasive plant management annually. Government staff provide expertise, education, coordination and facilitation services to all agencies, NGOs, regional weed committees and the Invasive Plant Council of BC. Despite the challenges created by a large land base and small tax base, BC boasts numerous significant achievements. The provincial-scale weed containment program, formalized early detection and rapid response, online database, leading-edge biological control, economic analyses, and weed ranking tool are measures of our success and collectively form the comprehensive and strategic provincial program. This coupled with strong public interest in protecting the environment will maintain the momentum necessary for positive change as BC manages invasive plants, their vectors, and pathways.

Weed control is still a challenge in non-transgenic sweet corn due to the suite of weeds present (including wild proso millet and triazine resistant species) and conservation tillage systems that are evolving to meet challenges of environmental stewardship and increasing input costs, mainly the rising costs of fuel and fertilizer. The HPPD herbicides tembotrione and topramezone are labeled and widely used, and have greatly improved the potential for one-pass POST weed control. But challenges still remain when using these herbicides in conservation tillage systems, notwithstanding potential crop injury when these herbicides are tankmixed with soil-applied herbicides such as s-metolachlor.

Experiments conducted from 2007 through 2010 evaluated weed control in strip tillage and conventional tillage corn with one-pass HPPD herbicide treatments, sweet corn tolerance to tank mixes of HPPD and chloroacetamide herbicides, and potential causes of injury. Experiments were located in the Columbia Basin near Prosser, WA and the Willamette Valley of OR. HPPD herbicides tank mixed with chloroacetamide herbicides and applied at V2-4 in 2007 damaged corn leaves, but the symptoms were transient and did not resemble symptoms commonly associated with chloroacetamide injury in sweet corn. In strip-tillage corn in OR in 2008, weed control was exceptional with topramezone plus s-metolachlor or dimethenamid-P but may have reduced corn yield by 20% or more at one of two experimental sites when applied at V5-6. In 2009 at trials near Prosser and at Corvallis, yield of both Coho and Basin varieties was reduced by 10 to 15% when topramezone and tembotrione were applied at V2. Yield of these two varieties was reduced by as much as 25% when water was poured over the corn plants before applying the tank mix of HPPD and chloroacetamide herbicide in 2010. And finally, HPPD herbicides had little to no effect on nutsedge in a strip-till field in 2010 unless tank mixed with bentazon or halosulfuron, but there was no significant injury to the corn and yield was not reduced. One-pass herbicide applications in sweet corn may require lower rates of chloroacetamide or HPPD herbicide when they are tank mixed, or possibly lower rates of the adjuvants typically used to enhance efficacy, but the precautions needed to limit injury may depend on corn variety, stage of growth, and soil and plant moisture when herbicides are applied.

Alion is a preemergence herbicide with the new active ingredient, indaziflam, Bayer CropScience has developed for use in perennial tree nut, fruit, and vine crops.  Registration is currently under review and pending approval by EPA.  Field trials have been conducted by Bayer CropScience, university, and private researchers across the United States in major fruit and tree nut production areas to evaluate weed control by indaziflam.  In these trials 73 g ai ha-1 indaziflam (5 fl oz Alion per acre) provided effective residual control of the most common monocot and dicot weeds.  Indaziflam alone provided insufficient control when applied postemergent to weeds.  Tankmixtures of glufosinate plus indaziflam provided both postemergence and residual weed control.  Residual weed control was similar or superior to rimsulfuron, flumioxazin, and oxyfluorfen.  Excellent crop tolerance was observed in all of these trials.

Efficacy trials conducted in 2007-2010 indicate that preemergent applications of indaziflam provided effective grass and broadleaf weed control in Pacific Northwest perennial crops.  Trials conducted by Universities, private researchers, and Bayer CropScience included evaluations in apples, pears, cherries, grapes and filberts grown in WA and OR.  Various rates of indaziflam, tank mixes with burndown herbicides, and combinations with other herbicides were evaluated for broader overall spectrum and resistance management.    Final weed control assessments in these studies confirmed the broad spectrum and length of residual activity as well as the excellent crop tolerance from indaziflam.  Upon registration (anticipated in 2011), indaziflam will be marketed for  extended residual control of broadleaf and grass weeds in perennial crops as Alion^TM.    

Two field research trials were conducted at the Aberdeen Research and Extension Center in 2010. The first included pyroxasulfone applied preemergence to weeds and potato at 0.106 or 0.213 lb ai/A alone or combined with flumioxazin; or pyroxasulfone at 0.213 lb/A plus pendimethalin at 1.0 or metribuzin at 0.5 lb ai/A. Treatments in the second trial were pyroxasulfone applied preemergence alone at 0.213 lb/A or with EPTC at 4.0, ethalfluralin at 0.75, or rimsulfuron at 0.023 lb ai/A. Nontreated weedy and weed-free controls were included in both trials for yield comparisons. Season-long common lambsquarters control by pyroxasulfone alone in either trial was less than 60 percent while control in the first trial was improved to 78, or 80, 100, or 100 percent by tank mixing the low rate with flumioxazin, or the high rate with flumioxazin, pendimethalin, or metribuzin, respectively. Tank mixing in the second trial with EPTC or ethalfluralin improved common lambsquarters control to 92 and 95 percent, respectively, however, control with pyroxasulfone plus rimsulfuron was only 62 percent. In general, season-long redroot pigweed and green foxtail control was greater than 90 percent regardless of treatment. Hairy nightshade control in the first trial was more than 95 percent while control in the second trial was 82 to 88 percent. Although there as a trend towards lower U.S. No. 1 and total tuber yields with the pyroxasulfone alone treatments compared with tank-mixture yields, all herbicide treatment yields were usually greater than nontreated weedy yields and not different than weed-free yields.

Aminopyralid, an auxinic herbicide that is very effective on several broadleaf weeds, is commonly used in range and pastures.  Potatoes are very sensitive to aminopyralid, and a number of off-target injury occurrences prompted this research.  Potato response to aminopyralid was evaluated under several off-target scenarios: fall soil applied carryover, preplant drift, in season response to early and mid season drift events, and daughter tuber plant response to late season drift onto potato foliage.  Picloram, dicamba, and clopyralid were included for comparison.  Following fall soil carryover applications of aminopyralid, potatoes planted the following spring showed little to no injury early season, but injury increased as plants grew.  Total yield was not significantly affected by fall applied soil carryover, but the highest rate (9 g ai/ha) resulted in a significant reduction in tuber quality (40% less US #1) compared to the untreated.  A field use rate ranges from 53 to 123 g ai/ha.  Spring preplant applications caused greater injury at lower rates than fall carryover applications, including early season injury, and resulted in significant yield losses (LSD P=0.1) at rates as low as 0.44 g ai/ha of aminopyralid.  In season applications were made 2 weeks after emergence (WAE) and again 4 weeks later at row closure.  Foliar injury was observed 1 to 2 weeks after both applications at all but the lowest rate (0.04 g ai/ha).  The highest rate at both applications (44 g ai/ha) resulted in a significant total yield loss, and 4.4 g ai/ha applied at 2 WAE also resulted in a reduction of tuber quality.  Late season simulated drift onto potatoes in 2009 resulted in foliar injury symptoms of plants grown from daughter tubers in 2010 beginning at emergence from rates as low as 0.44 g ai/ha, but symptoms were reduced as plants grew and there was no significant yield loss at this rate.  A rate of 4.4 g ai/ha of aminopyralid in 2009 reduced both stand and yield in 2010.  Preplant and in season applications of picloram caused similar levels of injury and yield loss at equivalent rates of aminopyralid.  Growing out daughter tubers of potatoes is one of the most sensitive bioassays for picloram.  Dicamba reduced yield when applied in season but not when applied preplant.  Clopyralid caused less injury overall than the other herbicides and reduced yield when applied preplant but not when applied in season.  Greater rates of clopyralid and dicamba were required to cause injury.  In addition to yield losses, there were greater numbers of tuber defects in aminopyralid treated tubers from all treatment timings.  These defects included growth cracks, knobs, folds, surface defects, and an unusual tuber defect involving a circular swelling around the eye resembling a bull’s eye.

An organic vineyard was established in Mount Vernon, WA in 2009 to analyze the effectiveness of cover crops compared to tillage for weed control. Five treatments were applied to ‘Pinot Noir Precoce’ (PNP) and ‘Madeleine Angevine’ (MA) grapes during the first two years of establishment: 1) tillage between rows, hand-weeding in rows (standard), 2) ryegrass cover between rows and tillage with the Wonder Weeder in rows, 3) winter wheat cover crop, 4) winter pea cover crop, and 5) 2:1 winter wheat and winter pea respectively. MA produced more shoot growth than PNP in September 2010, with mean lengths of 123.8 and 93.6 cm, respectively. Grapevines measured 160.4 cm under Treatment 1, significantly longer than vines under Treatment 2 (124.8 cm) or under the three cover crop treatments (from 82.3 to 91.2 cm). Weed biomass in September 2009 was maximized in Treatment 4 (10.8 g·m^-2), significantly greater than under Treatments 1 and 3 (3.6 and 1.6 g·m^-2, respectively).  The greatest weed biomass in July 2010 was produced in cover crops (Treatments 3, 4, and 5), ranging from 7.9 to 12.6 g·m^-2; by September, however, weed biomass did not statistically differ between treatments.  In 2009, most weed biomass was from within the grape row rather than between the rows, but in 2010, most of the weed biomass was from between the rows. A total of 1.7-hr·ha^-1 per person was required for plot maintenance in Treatment 1 for the two growing seasons, significantly longer than Treatment 2 (0.7-hr·ha^-1) or cover crop treatments (0.9-hr·ha^-1).

June-bearing strawberry cultivars are grown in a perennial matted-row system in western Washington.  Typically, establishment occurs in Year 1, followed by harvests in Years 2 and 3.  If plants are still healthy, they may be kept beyond the normal two harvests.  Since cultivation in the perennial bed is not possible, weeds within the rows after establishment are a major problem for producers.  Sequential herbicide combinations to winter-dormant strawberries were tested over the last two years at Washington State University Mount Vernon NWREC in effort to find combinations providing season-long control of common winter annual weeds such as common chickweed.  Split-block simazine at 1.1 kg ai/ha was applied in mid-December, followed by dormant-season, whole-plot treatments in mid-winter.  Although 29% of the treatments in 2009 did not result in greater than 10% foliar injury by March, 83% of the products resulted in greater than 10% injury when applied in sequence with simazine, and four of those resulted in greater than 20% injury.  By April, however, only strawberries treated with simazine + s-metolachlor and KSU 12800 with or without simazine were still showing greater than 10% injury.  In 2010, strawberry foliar injury from most dormant-season herbicides in March was comparable to the 23% injury observed in nontreated strawberries.  Injury was less than 10% by April for all treatments except KSU 12800.  Common chickweed control was much enhanced by use of simazine in 2009, measuring 89 and 53% control with and without simazine, respectively, when averaged across dormant season treatments.  In 2010, weed control was improved 15 to 22% when simazine was applied sequentially with dormant season herbicides.  Fruit yield did not differ by herbicide treatment either year, and simazine also did not improve total yield.  Average fruit weight was improved in 2009 by simazine treatment (16.7 and 14.8g/fruit for plants with and without simazine, respectively); fruit size did not differ in 2010.

Nebraska is now number one in the acres of irrigated farmland. The state moved to number one in 2007 replacing California. Average precipitation decreases 1 inch for every 25 miles from east to west across the state. Droughts are frequent in the High Plains and Nebraska records show 21 drought periods of 5 or more years in length in the years from 1220 to 1952. Nebraskans are always concerned about a drought and a depleting Ogallala aquifer that is forcing farmers to find more water efficient ways to produce crops. Some land that is now irrigated may have to return to rainfed or limited irrigation. Also, a large number of cropland acres in the High Plains will always be rainfed. The winter wheat fallow system was developed to compensate for the low precipitation in the high plains. Fallowing with tillage that buried most crop residues was replaced with tillage which left residues on the soil surface. Residue on the soil surface helps protect the soil from wind and water erosion. This stubble mulch lets more rain and snow soak into the soil to increase the soil water thus increasing efficiency. The crop residue also reduced soil temperatures to reduce evaporation of water from the soil. Winer wheat residue reduces weed density and improves weed management with herbicides. Crop Water Use (Evapotranspiration - ET) for irrigated corn in the High Plains ranges from 60 to 70 cm for fully watered corn. Up to 35% of this water use is from evaporation. Research has shown that the evaporation in fully irrigated corn can be reduced to as low as 15% of the ET with crop residues. This saving in E in ET plus saving 2.5 to 5.0 cm of soil water with the elimination of tillage reduces the irrigation water needs as much as 16 cm. Cropping practices for rainfed such as ecofallow and skip-row increase the success of crops grown using these systems. These practices are also being adopted by irrigators to increase crop water efficiency. This paper will discuss how to be successful with these water saving systems.

ABSTRACT

Penoxsulam Control of Conyza Species Biotypes in California

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

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

³Dow AgroSciences, Fresno, California

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

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

™^®Trademark of Dow AgroSciences LLC

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

Pyroxsulam is an effective herbicide for the control of key grass weeds and a wide range of broadleaf weeds in winter and spring wheat, including Durum.  Field studies were conducted with pyroxsulam (liquid oil dispersion formulation) in 2010 over a wide range of growing conditions, and against diverse weed species in California, Arizona and New Mexico.  In these studies, pyroxsulam was compared to a number of herbicides, including mesosulfuron, fenoxaprop and pinoxaden.  From the standpoint of grass weed control, pyroxsulam provided similar efficacy to mesosulfuron, fenoxaprop and pinoxaden against wild oat.  Against Italian ryegrass, pyroxsulam was superior to fenoxaprop and pinoxaden, but similar to mesosulfuron.  Against littleseed canarygrass, pyroxsulam was superior to all three.  For broadleaf weed control, pyroxsulam was superior to fenoxaprop and pinoxaden against wild mustard, bur clover, purple vetch and tansymustard, but similar to mesosulfuron.  Against nettleleaf goosefoot, pyroxsulam provided superior efficacy to all three comparison herbicides.  In assessments up to 30 days after application, pyroxsulam was slightly more injurious to wheat than mesosulfuron, fenoxaprop and pinoxaden, but this effect was not detected at later assessments.  Where broadleaf weed pressure was high, pyroxsulam generally resulted in higher yields than the comparison herbicides.  Pyroxsulam will be sold in California and Arizona under the trade name Simplicity^TM.

^TMTrademark of Dow AgroSciences LLC

State restrictions on the sale and use of Simplicity^TM apply. Consult the label prior to purchase or use for full details.  Always read and follow label directions.

Effective grass control in wheat has always been difficult to obtain without risking injury to the crop. This has become increasingly more difficult as Group 1 resistance has developed in some of the most important grass weeds. Pyroxsulam containing herbicides have demonstrated excellent control of many tough to control grass and broadleaf weeds while still providing excellent crop safety and rotational flexibility. Pyroxsulam herbicides are effective in controlling many of the toughest grass weeds in both winter and spring wheat, including but not limited to Italian ryegrass (Lolium multiflorum), wild oat (Avena fatua), and downy brome (Bromus tectorum), including Group 1 resistant biotypes. For use in winter wheat, a 7.5% wettable granule formulation (WG) of pyroxsulam  was registered in 2008, containing a 1:1 ratio with a safener, cloquintocet. During the 2009 and 2010 field seasons, we compared the currently sold formulation of pyroxsulam to a more concentrated WG formulation, containing 13.1% pyroxsulam, also in a 1:1 ratio with cloquintocet. Evaluations were conducted for control of several of the toughest to control grass weed species in winter wheat. Over the two years no differences in bioactivity or crop safety were observed between the two formulations of pyroxsulam. 

Broadleaf Weed Control in Wheat and Barley with Florasulam plus Fluroxypyr

Harvey Yoshida¹, Roger Gast², Monte Weimer², Marcin Dzikowski³

¹Dow AgroSciences, Richland, WA, ²Dow AgroSciences, Indianapolis, IN,

 ³Dow AgroSciences, Munich, Germany

Multi-year studies were conducted in the U.S. over 2008 - 2010 to evaluate the premix combination of florasulam plus fluroxypyr for postemergence broadleaf weed control in wheat and barley. The premix formulation, sold under the name Starane^® Flex by Dow AgroSciences, is a suspo-emulsion liquid containing a 20:1 ratio of fluroxypyr-meptyl (ae) and florasulam (ai). The labeled rate of florasulam at 987 mL formulated product per hectare (5 g ai/ha of florasulam plus 100 g ae/ha of fluroxypyr) resulted in excellent control of kochia (Kochia scoparia), wild buckwheat (Polygonum convolvulus), wild mustard (Sinapis arvensis), prickly lettuce (Lactuca serriola), catchweed bedstraw (Galium aparine), redroot pigweed (Amaranthus retroflexus), volunteer sunflower (Helianthus annuus), and Russian thistle (Salsola iberica). The combination of florasulam (Group 2) plus fluroxypyr (Group 4) provides advantages such as broad spectrum broadleaf weed control, short crop rotational flexibility and resistance management.

(^®Trademark of Dow AgroSciences LLC. Always read and follow label directions.)

Pyroxasulfone is a new selective herbicide under development for residual control of grass and broadleaf weeds in wheat production. Field research trials have been conducted across the USA from 2005 to 2009 to evaluate Italian ryegrass control and wheat safety from different application timings including preplant, preemergence, and postemergence. Rate ranges of pyroxasulfone from 25 to 250 g ai/ha have been tested for different application timings. Studies indicate that pyroxasulfone provides excellent control of Italian ryegrass and some other winter annual weeds with flexible application timing and long-lasting efficacy. No or little crop response was observed from most of the weed-free trials. These field trials show that pyroxasulfone can be an effective management tool for Italian ryegrass and other grass and broadleaf weeds in winter wheat.

Flucarbazone-sodium has been used effectively as a postemergent grass herbicide in cereal crop production since 2001.  Historically, flucarbazone-sodium’s selectivity to wheat was managed by limiting the stage of growth at application, restricting tankmix partners, and adjuvant use.  Recently, Arysta LifeScience has investigated flucarbazone-sodium in combination with the wheat safener cloquintocet-mexyl.    Everest 2.0 is a 419 g ai/l liquid suspension concentrate formulation containing flucarbazone sodium + cloquintocet-mexyl.  Cloquintocet-mexyl offers flucarbazone-sodium increased crop selectivity, in turn allowing more flexibility in its commercial use.   Flucarbazone-sodium crop injury under stress conditions or late postemergence applications is reduced by greater than half when in the presence of cloquintocet mexyl, while grass control is unaffected by the presence of the safener.   Averaged over trials, flucarbazone-sodium provided 92-94% control of wild oat (Avena fatua) when applied alone or in combination with safener.  With greater crop selectivity, more aggressive approaches can be taken to control difficult grassy weeds, which include using flucarbazone-sodium at 30 g ai/ha in combination with tribenuron-methyl and with surfactants containing a nitrogen source.   

Weed control in certified organic grain production in Eastern Washington presents many challenges. Spring crops, in particular, are weak competitors against weeds and often fail due to weed pressure. In May of 2010 an organic spring crop trial was initiated near Pullman, WA. The study addressed the relative competitiveness of six spring crops (barley, wheat, lentils, garbanzos, and peas) against oats. The experiment was a randomized complete block design with strip plots. There were four replications of treatments. Main plots included each crop planted at two different seeding rates (a recommended and a doubled rate) and subplots were two oat density treatments (88 kg/ha and 22 kg/ha) and a weed free control. The growth and development of crops and weeds were measured by stand counts, biomass, and yield. Crop stand counts for barley, wheat, and lentils increased when seeding rates were doubled, but due to recruitment, stand counts were similar for wheat and barley by 47 days after planting. Garbanzo, lentil, and pea stand counts were not affected by seeding rate or recruitment. Barley and wheat biomasses were greater than total weed biomass for each crop, while broadleaf crop biomass was less. Barley and wheat yields decreased as oat density increased whereas oat presence in the broadleaf crops resulted in a complete yield loss. Doubled seeding rates increased barley and wheat yields. Barley and wheat were the most competitive while the broadleaf crops were poor competitors.

Pyrasulfotole and bromoxynil is a relative new herbicide combination that has the potential to provide effective postemergence weed control of problematic weeds in grain sorghum. Fortunately, this herbicide combination also has the potential to control various groups of herbicide resistant weeds (triazine, ALS, and glyphosate).  Broadleaf weed control in grain sorghum continues to be challenging with limited options available, and weed resistance to those options occurring.  The second year of field experiments evaluating two application timings of a prepackaged mixture of pyrasulfotole and bromoxynil (1:8 ratio) plus atrazine alone, and in combination with 2,4-D ester or dicamba for grain sorghum tolerance and weed control were conducted near Tribune, Manhattan, Garden City, Colby, Topeka, Wichita, and Hays, KS in 2010.  Pyrasulfotole and bromoxynil at 244 g/ha was tank mixed with atrazine at 560 g/ha only or in combination with 2,4-D ester at 140 g/ha or dicamba at 140 g/ha.  Herbicide treatments were applied postemergence to 2 to 6-leaf (early) and 7 to 10-leaf (late) sorghum. Crop response and weed control were evaluated visually.  Sorghum injury ratings at all locations ranged from 0 to 30% injury 5 to 14 days after application for the pyrasulfotole and bromxoynil treatments.  Unlike 2009, the addition of 2,4-D ester or dicamba to pyrasulfotole and bromoxynil + atrazine did not consistently reduce sorghum injury compared to pyrasulfotole and bromoxynil + atrazine alone. At the six locations harvested, all pyrasulfotole and bromoxynil + atrazine treatments yielded similarly to the atrazine + bromoxynil treatments.  As for weed control, the highest level of control observed on palmer amaranth, redroot pigweed, tumble amaranth, common sunflower, ivyleaf moningglory, kochia, puncturevine, was consistently achieved across sites with the early application of pyrasulfotole and bromoxynil + atrazine treatments when weeds were typically 1 to 4 inches in height.  Weed control generally decreased with the later application of pyrasulfotole and bromoxynil + atrazine treatments when weeds were typically 6 to 9 inches in height.  For example, control for palmer amaranth was 96% when averaged across all sites and pyrasulfotole and bromoxynil + atrazine treatments for the early application and 86% for the late applications.  Puncturevine control was also reduced with an average of 94% control observed across all sites and pyrasulfotole and bromoxynil + atrazine treatments for the early application, while 73% was observed for the late applications.  Similar to 2009, the 2010 results indicate that grain sorghum has adequate tolerance to postemergence applied pyrasulfotole and bromoxynil + atrazine regardless of the tank mix partner evaluated in these experiments.  Excellent control of several problems weeds is an indication of the enhanced value the herbicide could bring to a weed control program in grain sorghum.  However, weed size is important in order to consistently observe high levels of weed control.

Early preemergence applications of pendimethalin in sorghum are only labeled east of the Mississippi river and in a few states and areas adjacent to the Missouri river as well as the state of Arizona.  This work was conducted to explore the possibility of expanding the range of this label.  To produce a robust weedy grass population, the entire plot area was seeded to winter wheat blended with green foxtail seed in the fall of 2006. In 2007 after wheat harvest, the entire plot area was kept free of broadleaf weeds with applications of 2, 4-D and dicamba as needed.  In 2008, the area was fallowed with light tillage and applications of 2, 4- D as needed to produce a dense stand of green foxtail.  The entire plot area was planted to winter wheat in the fall of 2008.   In 2009 on May 17^th the wheat was terminated with a 0.8 kg ai/ha application of glyphosate 30 days prior to planting sorghum.  Sorghum was planted without tillage on June 9^th at a rate of 99,000 kernels /ha.  Preemergence applications were applied immediately after planting followed by a 25 mm sprinkler irrigation to insure uniform emergence.  Treatments included preemergence applications of dimethenamid + saflufenacil at 0.9 + 0.04 kg/ha plus 1.1 kg/ha atrazine or 1 kg/ha pendimethalin applied to 30 cm or 3 to 4-leaf or spike stage sorghum.  For comparison, conventional treatments included preemergence applications of dimethenamid + saflufenacil + atrazine at 1.7 + 0.04 + 1 kg/ha or S-metolachlor + atrazine at 1.3+ 1.1 or saflufenacil at 0.04 kg/A.  Several permutations of  2, 4-D tank mixed with metsulfuron or carfentrazone or atrazine plus bromoxynil were also applied.  Experimental design was a randomized complete block with 4 replications.  Within 6 days of any herbicide application, 25 mm over head irrigation was applied to insure herbicide incorporation.  Sorghum was irrigated as needed to simulate a good dryland crop for this region.  Foxtail and crabgrass were the predominate weed species and no postemergence broadleaf compound performed well.  Low rates of atrazine in these postemergence treatments produced measureable albeit poor control on both grass species.  All preemergence grass control compounds produced greater than 90% control.  Treatments with spike applications of pendimethalin produced no injury as indexed by visual observation, and plant height.  In contrast, treatments containing pendimethalin applied to 30 cm sorghum had significant height reductions compared to the control and spike treatments of pendimethalin.  Tank mixes followed by spike applications of pendimethalin had the highest grain yield.  This yield was significantly higher than some standard treatments.  These results only represent one location and one year but strongly suggest that further work is needed on the timing and use of pendimethalin in grain sorghum.

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

Glyphosate resistance in Palmer amaranth is a major concern for farmers and weed managers.  Previous research has shown resistance to be due to increased copy number of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene through gene amplification, but the stability of this resistance trait is unknown.  We used qPCR to determine relative EPSPS copy numbers of F1 progeny from crosses between glyphosate resistant and susceptible Palmer amaranth.  Crosses included susceptible by resistant, resistant by susceptible, and resistant by resistant, creating twenty F1 populations.  EPSPS gene copy number was determined for at least ten plants from each of these F1 populations.  Preliminary data have shown a wide spread of copy numbers for the majority of F1 populations, indicating unstable transmission of copy number, with some populations exhibiting transgressive segregation.  One S x R 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 (determined by shikimate disc assay), as was expected.  More research on the EPSPS gene is needed to investigate how glyphosate resistance transmission occurs across generations at the molecular level.  However, our data are consistent with EPSPS gene amplification via transposition of a mobile genetic element.

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

Invasive knotweed varieties (Japanese, Bohemian and Giant) are a threat to riparian habitats because they reduce plant species diversity by establishing dense knotweed monocultures.  Multiple years of intensive surveys and chemical treatments are required to control the establishment and aggressive spread of this invasive plant.  The Nature Conservancy has been treating knotweed along river corridors in the Chehalis Basin of Washington State since 2004.  Given the cost and effort required to control knotweed, and other invasive plants, it is useful to characterize riparian areas with natural native seed regeneration, as well as plant recolonization capabilities.  Control efficacy studies typically measure the amount of knotweed reduced with treatment, but not the resulting plant community after treatment.  The objective and assumed outcome of these restoration efforts is a return to a native plant assemblage.  To examine this assumption, we measured the diversity and composition of plant species in riparian areas treated for knotweed and areas that never had knotweed.  We present plant community composition results from four streams 2 to 6 years after initial knotweed treatment.

Feral rye, an obligate out-crossing winter annual grass of the same species as cultivated rye, is a major crop pest in Colorado wheat. Recent studies indicate great genetic plasticity in regards to feral rye imazamox tolerance in Colorado and Oklahoma populations. Temperature can play an important role in herbicide efficacy, particularly in metabolized herbicides such as imazamox. Imazapyr was added to imazamox to discern if this combination would be more effective than imazamox alone at equal total active ingredient. A ¹⁴C translocation experiment and greenhouse experiment were carried out to investigate this issue. Imazamox movement in the plant was similar whether imazapyr was present or not. Imazapyr movement was greater and more rapid than imazamox. At the whole plant level, adding imazapyr to imazamox was always equal to or better than imazamox alone, under different temperature regimes and in different formulated ratios. Imazamox activity appeared to have a temperature correlation whereas imazapyr did not. This indicates addition of imazapyr may be better for feral rye control in late fall and early spring where low temperature can occur for extended periods in some areas of the country.     

A long-term field study was conducted near Scottsbluff, NE from 1998 to 2009 to identify weed-shifts in response to glyphosate-resistant cropping systems. The study was designed as a split-split plot RCBD where the whole plot factor was crop rotation, the split plot factor consisted of glyphosate use patterns, and the split-split plot factor was presence or absence of a PRE herbicide. Glyphosate use patterns ranged from treatments receiving no glyphosate to continuous, exclusive use of glyphosate. In 2010 weeds were allowed to establish without herbicide treatment or crop competition and then counted. To interpret the weed density counts, a competitive index of each weed species as if it was in competition with corn, dry bean, and sugarbeet was used to calculate the competitive load for the weed spectrum resulting from historical treatments. The previous crop rotation had no effect on competitive load regardless of the crop index used. For the corn competitive index, treatments utilizing a PRE herbicide, or continuous use of glyphosate at 840 g ae ha^-1 resulted in the lowest competitive load. For both the dry bean and sugarbeet competitive indices, the use of a PRE herbicide significantly decreased the competitive load, regardless of glyphosate use history. Continuous use of glyphosate at 840 g ae ha^-1 resulted in the lowest competitive load of any glyphosate use history for both the sugarbeet and dry bean indices; however there was no statistical difference between this treatment and alternating glyphosate applications with conventional herbicides when using the sugarbeet index.

Mechanistic understanding of processes by which crops and weeds affect each other provides the foundation for effective management strategies. While resource competition has been a dominate paradigm of plant interactions, recent work in natural systems is increasingly demonstrating the importance of alternate mechanism, plant-soil biota feedbacks (PSF), where interactions among plant species are mediated through effects of plant species on soil microbial communities. However, in agricultural systems, effects crop and weed species on abundance and composition of soil microbial communities (SMC) and how SMC feedback to affect crop and weed growth have not been explored. Furthermore, while fertilization and tillage are known to alter the diversity and function of SMC, the impacts of these management practices on PSF is unknown.  To investigate the effects on PSF on crop-weed interactions, we conducted a greenhouse experiment in which biomasses of four crop species were compared following treatments of weed and crop species grown in monoculture in soils that had been inoculated with SMC's from agricultural sites, non-agricultural sites, or sterilized controls. The results demonstrate that the nearly half of the impacts of weeds on crop growth are mediated through PSF, that effects of PSF differ among plant species, and that these effects are altered by agricultural practices. 

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. and some cancers. Malaria has developed a resistance to most drugs currently used, making artemisisin one of the last known modes of treatment and leading to high worldwide demand. However, to date, artemisinin cannot be produced in large amounts synthetically due to its complex structure, requiring extraction from A. annua. As yields of artemisinin are very low (0.01%-0.80%), development of new cultivars and understanding the biosynthesis and conditions influencing artemisisin yield are essential. 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. A. annua was transplanted on three dates, May 10, June 10, and June 16, 2010, at Central Ferry, WA.  At anthesis, plants transplanted on May 10 reached a mean height of 142 cm (+/- 2.1) with 674 g (+/- 49.2) of dry biomass accumulation. Compared to the last planting date, June 16 with a mean height of 117 cm (+/- 2.4), and dry biomass was also lower, at 357 g (+/- 28.5). In addition, at anthesis a total of 572 g/HA (+/- 103.9) of ART can be harvested. 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.

Imazapic (0.188 lb a.e./A + MSO 1 qt/A) was applied once in the fall and on two sequential years in the fall at two sites with difference abundances of sympatric leafy spurge (Euphorbia esula) and dalmatian toadflax (Linaria dalmatica). Control of leafy spurge canopy cover was 86 to 97% for the first year post-spray. Treating leafy spurge with imazapic in two sequential years did not increase the absolute level of canopy cover control but did extend the duration of a high level of suppression. Spraying reduced leafy spurge frequency of occurrence, but the remaining resprout frequency was quite high and sufficient to probably allow leafy spurge to eventually re-dominate the sites. Spraying twice did reduce leafy spurge frequency of occurrence to a low level. Imazapic provided acceptable control of dalmatian toadflax where its initial abundance was low and the site was proportionately much more dominated by leafy spurge. However the dalmatian toadflax actually increased after spraying relative to the no-spray controls on the second site where dalmatian toadflax had a higher absolute abundance and was proportionally more similar to the leafy spurge abundance. Competition between post-spray resprouts of dalmatian toadflax and leafy spurge were determining the relative responses of the two targets. Leafy spurge is more susceptible to imazapic, and when dalmatian toadflax is well established and vigorous the toadflax benefits from the suppression of the leafy spurge. The sequentially sprayed twice treatments released spotted knapweed (Centaurea stoebe) from competition with imazapic susceptible species. The imazapic treatments suppressed sulfur cinquefoil (Potentilla recta), but the level of control was not high enough to recommend imazapic as an efficacious herbicide for sulfur cinquefoil. First year post-spray declines in perennial grass canopy cover corresponded to observed and known imazapic visual injury symptoms. These symptoms consisted of reduced culm height and suppressed flowering. Perennial grass recovery was obtained by the second year post spray, but there were only limited net gains in perennial grass production. Species richness was fully restored within 2 to 3 years after spraying imazapic once. Additional reduction in competition from spraying twice allowed complete species richness recovery in the second year after cessation of the treatments. Imazapic did not reduce non-target forb canopy cover on the more diverse site. On the less diverse site with much less initial non-target forb canopy, the non-target forb canopy cover was fully recovered in the second year after ending spraying. Decreaser species strongly outnumbered increaser species in the first year post-spray once or twice at both sites. However the principal community level effect of spraying was to alter the intensity of competitive interactions between the numerous individual species. Previously scarce resources, most importantly soil moisture in these somewhat xeric environments, were now available allowing many species population abundance shifts. The opportunities for establishing individual new plants were further enhanced by reductions in accumulated litter and creation of bare soil safe microsites. The ratio of increaser species to decreaser species improved greatly starting in the second year post-spray. The number of increaser species came into approximate balance with the number of decreaser species. The target weeds, both the forb weeds and the annual grasses, generally remained decreasers. Statistically significant native forb increasers included fringed sage (Artemisia frigida), yarrow (Achillea millifolium), and hairy golden aster (Chrysopsis villosa). Native forbs exhibiting tolerance, that is no change in abundance, included silky lupine (Lupinus sericeus), low larkspur (Delphinium bicolor), arrowleaf balsamroot (Balsamorhiza sagittata), and fuzzytongue penstemon (Penstemon eriantherus). Imazapic provides an efficacious but more selective option for suppression of leafy spurge than picloram when conservation of desirable plant species is an important management goal.

On the Island of Hawaii, a recent history of the windward slope on Mauna Kea (1500-2500 m) includes deforestation, exotic forage species introductions, and active grazing management over the last 150 years. Today, a new history is being scheduled to restore critical native plant communities across 1000’s of hectares. Despite being in a tropical climate, this high elevation landscape experiences frost temperatures during the winter months, which inhibits planting of native seedlings at the wettest time of the year and poses a conundrum for only planting during the summer when soil moisture is a serious limitation. Following ungulate removal, the unchecked naturalized forage communities are the next greatest impediment to successful restoration. Moisture limitation is presumably exacerbated by the exotic occupants consisting of C4 (Pennisetum clandestinum) and C3 (Anthoxanthum odoratum and Holcus lanatus) grasses. A simple replicated experiment was installed to characterize the efficacy of herbicide applications in suppressing these resident grass communities as well as determine the effects the suppression treatments have on soil moisture availability. In May 2010, a replicated experiment was installed with glyphosate and imazapyr applied as individual treatments in 10 x 6 m plots at 1.12 and 0.56 kg ae/ha, respectively, and compared to an untreated control. Each plot was installed with soil moisture and temperature sensors (Decagon Devices, Inc. Pullman, WA) buried at 5 and 20 cm depths and coupled to data loggers programmed to record hourly. As expected, glyphosate showed observable symptoms of sod desiccation and profile reduction early (90 DAT), while the imazapyr treatment was less pronounced. However, both herbicide treatments were recorded with higher volumetric soil moisture levels (m³/m³, P<0.01) at a 5 cm depth compared to the untreated control, but were not significantly different between herbicide treatments. Furthermore, soil moisture was higher at the 20 cm depth, than at the 5 cm depth across all of the treatments, including untreated. Temperature data showed higher diurnal fluctuation at the 5 cm depth than at 20 cm. Our initial data analyses, suggest early suppression of competitive grasses attributing to an increase in soil moisture. Treatment affects are expected to shift over time due to differences in suppressive longevity between glyphosate and imazapyr. We will present trends of this data to include time points at 180 and 270 DAT. The ability to determine intervals of increased moisture retention resulting from suppressive pre-plant herbicide applications can be exploited for optimizing planting schedules post-treatment.

Long term studies present the unique possibility to monitor the impacts of weed management practices over weed populations. Changes in the dynamics of soil seed banks are often reported as variations in the total weed seeds. In addition the effects of herbicides programs are frequently evaluated by the number of weeds present two weeks after the last post emergence herbicide application. The analysis of total seed numbers in soil seed banks or the number of plants present after the last application can sometimes be misleading, particularly if the weed populations are shifting to more competitive species. The Competitive Load (CL) is used to describe the total competitive effect of a weed population. The CL is estimated based on the Competitive Index (CI), which is used to measure the relative competitiveness of a weed compare to a crop. The CI was used to determine its potential value in the analysis of long term weed management practices over weed populations. The CI was applied to weed seed bank data and to weed densities counts determined two weeks after the last post emergence herbicide application, from a long term study. The study was conducted between 1998 and 2009 at Scottsbluff, NE, to evaluate glyphosate induced weed shifts in a glyphosate resistant crop rotation. The use of the CL in seed bank analysis helped reflect changes in the potential competitiveness of the weed populations present in the soil seed bank. This advantage was minimized when the number of species present in the seed bank was reduced. The CL proved to be more promising when applied to weed densities determined after the last herbicide application. The CL increased through time with all herbicide treatments, suggesting changes in the species composition of the weed populations.         

Creeping bentgrass (Agrostis stolonifera) is a perennial, obligate outcrossing species mainly used on golf courses. Glyphosate resistant (Roundup Ready) transgenic creeping bentgrass was developed by Scotts Company and Monsanto.  While still a regulated article, it was planted in Oregon and Idaho for seed production. In Oregon, about 160 ha were planted in Central Oregon near Madras.  After swathing but before combining, a wind storm moved panicles from the fields.  The fields were removed from production in 2003.  Because the transgenic creeping bentgrass was still a regulated article, all transgenic creeping bentgrass plants were required to be found and destroyed.  Seven years after the removal of the fields, transgenic creeping bentgrass plants are still being found near the Madras fields.  In Idaho, production fields were planted in Canyon County under notification in 2003 and 2004 and under permit in 2005 and 2006.  It is not clear why there was a change from notification to permit for the production but a permit is more restrictive than a notification. According to Scotts Company, the size of the fields, the harvest dates, and the years the fields were removed are considered to be confidential business information. The fields likely were harvested in either 2005 or 2006 or both. Transgenic creeping plants were found in Canyon County after the fields were removed from production.  In October 2010, the presence of transgenic creeping bentgrass was confirmed in Malheur County in Oregon. Transgenic creeping bentgrass was never planted in Malheur County but Canyon County is just across the Snake River. The plants are likely the result of seed movement from the Idaho sites possibly on trucks or other equipment. The transgenic creeping bentgrass has spread along irrigation canals, ditches, and roadsides.  It also has been found in pastures and production fields.  The transgenic creeping bentgrass is still a regulated article. There were no mitigation plans for gene movement in place for either the Madras or the Canyon County sites.  There are no herbicides presently labeled that are permitted to be used along the water ways that are effective for controlling established glyphosate resistant creeping bentgrass.  The failure to consider creeping bentgrass biology, ecology, production practices, and control options led to the erroneous opinion provided by the Weed Science Society of America stating that Roundup Ready creeping bentgrass would not be a problem and could be controlled by other herbicides. The major issue not addressed in the opinion was that lack of herbicides that can be used near water ways where the most used and effective herbicide is glyphosate.  The authors failed to consider the potential for gene flow during seed production which is very different than what would occur in a turf situation.  This example of transgenic creeping bentgrass provides insight into the complexity of preventing gene flow, the inadequacy of the monitoring requirements, and the difficulty in retracting a gene once it is released let alone determining how far the transgene has moved.

In the last two decades ventenata [Ventenata dubia (Leers) Coss.] has spread rapidly along transportation corridors, in pasture, hay land, range and Conservation Reserve Program (CRP) fields throughout the Pacific Northwest.  Data collected in 2008 from a survey sent to Natural Resources Conservation Service (NRCS) field staff and an 800 km traverse through eastern and central Washington, northeastern Oregon and northern Idaho revealed ventenata grows in areas receiving 35 to 112 cm annual precipitation at elevations ranging from 10 to 1800 m.  It is most commonly found on south-facing slopes and in shallow, rocky clay or clay-loam soils that are saturated or inundated in early spring.  However, it can also be found on other aspects and soil types.  In areas with disturbance such as grazing, ventenata appears to be displacing desirable vegetation.  In undisturbed areas it may be replacing desirable vegetation as growth is hindered by old age, disease, or lack of nutrients, and may be preventing desirable vegetation from reproducing by occupying open niches.  Ventenata is a winter annual grass in the Aveneae tribe that has a shallow root system, one to few tillers and produces 15 to 35 seeds per plant.  Ventenata seed has a bent and twisted awn which, similar to wild oat (Avena fatua L.) “unwinds” when it becomes wet and drills the seed into the soil.  Seed typically germinates in the fall about 2 weeks after downy brome (Bromus tectorum L.).  Similarly, ventenata produces seed heads in the spring 2 to 4 weeks after downy brome.  Greenhouse experiments indicate vernalization is necessary for seed head production.  Ventenata seed has little or no innate dormancy, however dormancy may be induced if seeds are exposed to cold temperatures.  Seed placed in a germinator at 18 C with 10 hours of light began germinating on Day 4 and achieved 85% germination by Day 26.  Seed chilled for 5 days at 1 C prior to being placed in germinator began germinating on Day 9 and reached a maximum of 30% germination on Day 68.  Seed chilled for 10 days at 1 C began germinating on Day 31 and reached a maximum of 35% germination on Day 64.  In soil, seed may be viable for only 1 or 2 years.  Seed in packets buried at 2 cm and 8 cm at two sites had an average germination of 82% and 80%, respectively, after 1 month and 0% germination after 6 months.  After 1 year there was one germinating seed (at 2 cm depth) indicating there may be a small amount of variability in dormancy.  Grazing and mowing ventenata are not effective management options.  If the plant is grazed or cut when soil moisture is available it will regrow from within the same tiller and produce viable seed.  Depletion of soil moisture is typically a trigger for seed head production, and during this phase the plant has high silica content (~2.7%) which causes it to become unpalatable to livestock and difficult to mow or swath.  Fire is also not an effective management option; survey respondents reported in areas where fires have occurred, ventenata is more prevalent.  Ventenata is of ecological concern because it may impair the functions and productivity of grassland systems.

The export market for Timothy hay has been $200 to $215 per ton for the last several years.  Ventenata has matured at the optimal time for Timothy harvest and even small amounts in a bale can cause its rejection for export.  The domestic market is $70 to $100 per ton so losses because of ventenata can be as high as $145 per ton.  It is possible to avoid rejection by harvesting early but unstable weather during June can make early harvest risky.   Optimal timing for Timothy coincides with ventenata maturity and ventenata stems are difficult to cut, requiring sharpened sickles  and ground speed must be slow.  Seeds spread throughout the field during harvest, quickly infesting a field even with small initial infestations.  Once well- infested and Timothy production is reduced, the field must be plowed in June and cultivated through the summer and occasionally, a glyphosate application is made during the fallow period.  The field is then re-seeded either in the fall or the next spring.  Normally, Timothy is not harvested during its first year and ventenata is not detected but during the second or third year some ventenata usually is detected.  Once detected, the field likely will need to be reseeded in two years.  We have tried several herbicides in test plots that include metribuzin that must be applied before ventenata is 2 inches tall but results were erratic.  Sulfosulfuron is effective but crop injury ranges from no damage to 50% damage with damage seen when Timothy had sprouted in the fall and the growing season was unusually wet.   Aminopyralid has been effective as a preemergent at the high end of the label rate but we are not able to sell for export.  Challenges continue for hay production and we are still needing to work towards additional options for management of ventenata.

Ventenata is an annual grass weed that is difficult to control especially in hay and grass seed crops including Kentucky bluegrass and timothy. Few grass herbicides are registered for use in Kentucky bluegrass, while none are registered in timothy. Studies were established near Plummer, ID in Kentucky bluegrass and near Potlatch and Gifford, ID in timothy to evaluate weed control and crop injury with various grass herbicides over the growing season. The experimental design was a randomized complete block with four replications and included an untreated check. In Kentucky bluegrass, ethofumesate, pendimethalin, metolachlor, terbacil, pyroxsulam and flufenacet/metribuzin alone or combined with terbacil, primisulfuron, and oxyfluorfen controlled ventenata 74 to 100%. Flufenacet/metribuzin at the high rate injured Kentucky bluegrass 29%, but injury was greatest with pyroxsulam at 80%. In timothy at Potlatch, triasulfuron, sulfosulfuron, terbacil, rimsulfuron, and flufenacet/metribuzin alone or combined with sulfosulfuron or triasulfuron reduced ventenata stand 90% or greater compared to the untreated check. Timothy stand height and seed head formation were reduced 26 to 35% and 10 to 25%, respectively, by rimsulfuron, terbacil and sulfosulfuron at the high rate. At Gifford, ventenata control in timothy was 90% or greater with metolachlor, ethofumesate, diclofop, primisulfuron, oxyfluorfen plus diuron, pyroxsulam, and flufenacet/metribuzin alone or combined with terbacil, flucarbazone, diclofop, aminopyralid, sulfosulfuron, and primisulfuron. Timothy injury was 14 to 21% with flufenacet/metribuzin alone or combined with terbacil, diclofop, sulfosulfuron, and primisulfuron. Dry forage hay weight did not differ among treatments and from the untreated check.

Ventenata (Ventenata dubia) is an annual grassy weed that degrades range and wild lands of the Pacific Northwest. Research was established in 2008 on the Warm Springs Reservation and consisted of two sites, one where bluebunch wheatgrass remained despite significant populations of ventenata, and a second nearby location where few bunchgrasses remained. Treatments at the two locations consisted of herbicides-only and herbicides followed by planting of different bunchgrass species. In the spring of 2009 herbicide-only applications provided 100 percent control of ventenata in the herbicide-only plots. The following season residual efficacy for the four herbicides dropped to 60 and 68 percent for imazapic plus glyphosate or imazapic alone, 73 percent for rimsulfuron and 81 percent for sulfometuron plus chlorsulfuron. Where six bunchgrasses species were planted directly following herbicide application of imazapic alone or with glyphosate, a moderate stand of Sherman big bluegrass, Sandberg’s bluegrass and intermediate wheatgrass were established in the spring of 2009. Stand establishment in the sulfometuron plus chlorsulfuron and rimsulfuron treated plots planted during the fall of 2009 was strong for Sandberg’s bluegrass and Sherman big bluegrass, and moderate for smooth brome and intermediate wheatgrass. Differences in stand establishment during the spring of 2009 and 2010 were likely due to spring precipitation, and timing and duration of cattle present in the plots.

The Palouse prairie ecosystem is endangered and the remnants are being further degraded by downy brome and ventenata.  Four studies were conducted to evaluate herbicide effects on Palouse prairie plant communities and downy brome and ventenata control.  Species richness in pyroxsulam, diclofop, and propoxycarbazone treatments were similar, 5.0, 4.4, and 4.4 species respectively, indicating these treatments were the least injurious to the native plant population.  Pyroxsulam, sulfosulfuron, and imazapic plus glyphosate treatments reduced alien grass richness to 0.9, 0.8, and 0.8 species, respectively, compared to 1.8 for the nontreated areas.  Imazapic plus glyphosate and sulfosulfuron reduce alien grass cover 73% and 69% respectively, and were similar in control to pyroxsulam, chlorsulfuron, and diclofop.  Control of downy brome was 87% or greater with sulfosulfuron and imazapic plus glyphosate.  Ventenata control was 77% or better by diclofop, sulfosulfuron, pyroxsulam, and imazapic plus glyphosate.  Treatments of diclofop, sulfosulfuron, pyroxsulam, and imazapic plus glyphosate were the most effective herbicides for downy brome and ventenata control and the safest on the native plant community.

Ventenata is able to establish in a wide range of habitats in the Inland Northwest including pasture, rangelands and grass hay.  Extension outreach programs suggest that among these habitats, natural and managed perennial grass systems including grassland prairies, pasture, and Conservation Reserve Program (CRP) are increasingly impacted by ventenata and are in need of applied research to develop management techniques. In the Palouse Prairie, ventenata is one of the primary weeds impeding restoration efforts of prairie remnants.  In pasture systems, small-farm owners have seen forage yields decline as much as 75% following ventenata invasion.  In CRP, ventenata’s displacement of resource-conserving vegetative cover has made compliance of maintenance requirements difficult and has negative impacts on the wildlife habitat objectives of the program.  Initial extension-directed research efforts have concentrated on identifying herbicide control options across a range of production systems.  The objective of these efforts was to identify appropriate application rates and timings of labeled products that achieve high levels of ventenata control while minimizing injury to desirable grasses in each production system.  Few products are labeled for annual grass control in non-agronomic commodity systems and fewer are labeled specifically for ventenata control.  In 2006-2008, field studies were conducted in ventenata-infested grassland where bluebunch wheatgrass and Idaho fescue were the primary perennial grasses.  Applications of imazapic at 1.75 oz ae/A and sulfosulfuron at 0.75 oz ai/A applied in late fall, following ventenata germination (<1” tall), resulted in high levels of control (>90%) and less than 50% growth suppression of perennial grass.  Subsequent studies showed that high levels of ventenata control could be achieved with imazapic + glyphosate or terbacil applications applied in late fall to emerged ventenata seedlings.  Terbacil applications resulted in less injury to perennial grasses in comparison to imazapic + glyphosate.  Another  study was conducted in 2007-2009 in a pasture comprised of bearded wheatgrass, meadow foxtail, smooth brome and Sandberg bluegrass.  Plots were located in areas of low (<25%), medium (40-60%) and high (>75%) ventenata foliar cover.  Imazapic was applied at 1.1 oz ai/A in the spring and NPK fertilizer (160 lb N/A) was applied as a split application to sub-plots.  Significant injury to perennial grasses was observed.  Fertilizer-only applications resulted in increases to perennial grasses 15 MAT comparable to increases observed in herbicide-only plots in both medium and high ventenata cover plots.  Inferences from comparisons between fertilizer and herbicide treatments across varying levels of ventenata cover were somewhat conflicted by herbicide injury to perennial grasses, but results indicate that management targeted towards nutrient pools and cycling may be critical to development of integrated control strategies in perennial grass systems.  Sulfosulfuron has been demonstrated as effective for ventenata control but little is known about the effect of sulfosulfuron on emerging or emerged perennial grass seedlings.  In 2010, a greenhouse study was initiated to determine the effect of sulfosulfuron on 11 perennial grasses commonly found in CRP, pasture or grassland plantings.  These grasses were planted into six rates of sulfosulfuron, ranging from 0 to 0.75 oz ai/A.  Initial results indicate that intermediate and bluebunch wheatgrass are generally tolerant across the range of sulfosulfuron rates, whereas grass yields decline significantly at low rates of sulfosulfuron across all other species including bromes, bluegrass and timothy suggesting a limited choice of grasses can be used for reseeding if sulfosulfuron has been applied recently.  Management of ventenata continues to be a challenge but a fertilization program linked to herbicide application will contribute to a ventenata decision tool to assist farmers and ranchers.

Ventenata dubia is one of a complex of weedy annual grasses that infest rangelands as well as pastures, CRP and hay fields. Detecting annual grasses and other weeds from perennial grasses on rangelands presents a significant challenge. This challenge may be addressed by using remotely sensed data to develop landscape level decision tools for making weed control and plant community rehabilitation decisions. Decision tools are being developed that utilize plant cover as one component. Hyperspectral data (126 bands in visible and infrared wavelengths) of the Canyon Grasslands in northern Idaho between Grangeville to south of Riggins, ID along the Salmon River were collected using an aircraft mounted instrument. The hyperspectral data from a small accessible area of the grasslands were subjected to an unsupervised classification and compared to an initial set of ground referenced polygons containing different vegetation types collected at the site; this initial classification did not successfully distinguish degraded areas with annual grass and broadleaf weeds from areas with desirable perennial grasses. Additional polygons containing different types of vegetation were collected at various accessible sites on the landscape using a handheld GPS-GIS unit and used to develop signature files. These signature files were in turn used to develop a supervised classification of the landscape that was able to distinguish to some degree between different vegetation types. Further cycles of collecting ground referenced data and developing signature files can be used to refine the landscape classification. Making larger scale plant community improvements on public lands can be driven by major disturbances such as fire when resources are made available for recovery after fire. Classifying rangelands by categories of annual grass cover would allow implementation of decision tools across the landscape scale needed to assist in making informed decisions on where to spend resources after fire.

Chemical control of saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia L.) has had varying degrees of success.  Often, these trees are mechanically removed but the stumps are not treated so they readily regrow.  Some non-selective herbicides used to control these invasive plants cause unacceptable injury to desirable species, especially grasses in the understory, or do not control other invasive plants under the tree canopy.  Aminopyralid (Milestone^®) controls many invasive herbaceous broadleaf weeds, but control of saltcedar and Russian olive had not yet been fully explored.  Experiments were established in Nebraska, Colorado, and Wyoming to assess the efficacy on saltcedar and Russian olive regrowth or small trees and understory grass tolerance to aminopyralid plus triclopyr (Garlon^® 3A or Garlon^® 4 Ultra) mixtures and combinations with lower than recommended rates of the commonly used herbicide, imazapyr.  Lower than recommended rates of imazapyr were used in an attempt to reduce injury to desirable understory grasses and improve saltcedar control with mixtures of aminopyralid and triclopyr.  Treatments included triclopyr amine at 3.37 or 4.5 kg ae/ha (3 or 4 lb ae/A) and triclopyr ester at 2.24 or 3.37 kg ae/ha (2 or 3 lb ae/A)  plus aminopyralid at 120 g ae/ha (0.l1 lbs ae/acre), Milestone^® VM Plus at 9.6 L/ha [triclopyr amine at 1.12 kg ae/ha (1 lb ae/acre) plus aminopyralid 120 g ae/ha (0.11 lb ae/acre)], and combinations of imazapyr at 0.14 and 0.28 kg ae/ha (0.125 and 0.25 lb ai/acre, respectively) with some aminopyralid plus triclopyr treatments.  At 326 days after application, 3.3 kg ae /ha (3 lbs ae/acre) triclopyr ester plus 120 g ae/ha aminopyralid provided excellent control (98%) of Russian olive and saltcedar (94%), similar to efficacy of imazapyr at 1.12 kg ae/ha (1 lb ae/acre) but with significantly less understory grass injury. Triclopyr plus aminopyralid treatments caused little to no grass injury (0 to 5%) compared to the imazapyr treatments (50 to 85%).  Addition of imazapyr to aminopyralid plus triclopyr did not improve control of either brush species, but increased grass injury compared to aminopyralid plus triclopyr.  At the Colorado site, aminopyralid plus triclopyr amine tended to cause more grass injury than aminopyralid plus triclopyr ester, but caused less injury than than when imazapyr was included in treatments. Adding aminopyralid to either the triclopyr amine or triclopyr ester increased control of Russian olive and saltcedar.  The combination of aminopyralid plus triclopyr is an excellent option to  control Russian olive and saltcedar  without injuring  desirable understory grass vegetation.