Brief Summary of Minutes of Annual Meeting

BRIEF SUMMARY OF MINUTES OF ANNUAL MEETING: 

We met in Maui, HI at the Hyatt Regency Resort on Monday, March 2, 2020 from 2:00 pm to 4:00 pm, before the annual joint meeting of the Weed Science Society of America/Western Society of Weed Science.

The meeting was initiated with a review of the new, approved WERA 077 Proposal:

• New Objectives Discussed
  • Integrated Management of downy brome, feral rye, jointed goatgrass, and Italian ryegrass
  • Reduce spread of critically important herbicide resistant weed species
  • Share information among members of group
  • Develop educational programs and disseminate information

Update on Past Discussed Studies:

• Feral Rye Project
• Objectives = flowering time, seed production, shattering, germination
  • Ian has much of the seed collected from group. New graduate student in WA that could assess samples in a beneficial way. If they cannot, seed will go to Vipan and/or Caio? And group can decide on what to do with those feral rye seed collections. Some members showed interest in conducting common garden study to understand the phenotypic differences across the region.

Ideas for Research Following New Objectives:

• Aggressor Application Timing in CoAXium Wheat
  • Oklahoma and Idaho have documented injury with Fusion variety when Aggressor applied near jointing stage
  • Disease interaction? Green bridge? Lodging/stunting/black meristem in Oregon?
  • Genomes conferring tolerance. Caio brought up discussion on the underlying mutations responsible for injury. Varieties with mutation on AA BB genome are less resistant and varieties with mutation on AA DD genome are high resistant?
  • Misha will send up follow-up email on this topic

• Italian Ryegrass Management
  • Group 1 and group 2 herbicides are mainly used for ryegrass control in OR, ID, OK—Ever increasing problem of resistance to group 1 and group 2 herbicides
  • No-till - one-time moldboard in the fall for burying seeds of Italian ryegrass if environment allows (ID)
  • Delay seeding can help in ryegrass control in OK, it may not work for other states
  • Increased pyroxasulfone rate along with other actives for ryegrass control in OR
  • Resistance to pyroxasulfone does not always equal cross resistance to flufenacet

• Downy brome Management
  • Main grass problem in WA, MT where no-tillage is widely adopted (>72% no till cropland in MT
  • Increasing problem of ALS resistance in downy brome in WA and MT. No resistance to powerflex in OR?
  • Ian brought up that glyphosate-resistant downy brome populations now identified in Washington with increased EPSPS gene copies as mechanism of resistance
  • Tim brought the discussion on a study in Wyoming by Dan Takeila, who is studying the downy brome seed longevity and persistence in rangeland
  • Group like to initiate some regional efforts on downy brome management

• Metribuzin and pH
  • No issues in PNW
  • pH issues driven down use in New Mexico

• New Herbicide Resistance
  • Downy brome to glyphosate in SE WA? Populations were eradicated?
  • Imazamox resistant feral rye (?), not necessarily cross resistant to sulfosulfuron
  • ALS-resistant goatgrass in WA and OR, especially imazamox? Some biotypes were also resistant to Osprey

• Soil Seedbank Study
  • Flowering time, seed production, shattering, germination

• Emerging Bromus
  • Sterile brome
  • Rescuegrass
  • Rattail fescue
  • True cheat (cross resistant to all ALS)

• Seedbank longevity
  • Feral rye as target?
  • How environments shift seed longevity
  • Impact of cultural practices on feral rye seedbank longevity

Other Business:

The 2021 meeting will take place on Monday, March 1, 2021 in Boise, Idaho. Time TBD, but likely at the same 3 PM time.

Vipan Kumar will be collecting the state reports (due 6 weeks from the meeting).

Selection of New Secretary/Chair Elect:

Caio Brunharo volunteered to be the new secretary/chair elect for next year. All the meeting participants agreed. Consequently, next year (2021) Vipan Kumar will organize and conduct the meeting and Caio Brunharo will take notes and file the annual report.

The meeting adjourned at 4:00 pm.

IDAHO REPORT

Objective 1. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 106 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used in our area to control Italian ryegrass. Untreated plants are included from each sample. For 2019, samples screenings are in progress for pyroxasulfone, metolachlor, dimethenamid and flufenacet. No sample is resistant to pyroxasulfone or glyphosate. Pinoxaden resistance is near 65% while pyroxsulam and mesosulfuron resistance is widespread (< 90%). The non-selective group 1 herbicides with resistance includes:  clethodim (15%) < sethoxydim (25%) < quizalofop (80%).

Objective 1. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop, and herbicide rotation, have altered the makeup of the population.

Objective 2. Results. A winter wheat/Italian ryegrass control study evaluated pyroxasulfone and flufenacet at the highest labeled rates with the following application times:  pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat. Italian ryegrass control was improved with flufenacet versus pyroxasulfone at all timings due to a higher rate of pyroxasulfone. flufenacet did not control Italian ryegrass and is most likely due to a resistant population. This study is being repeated in 2020. Pyroxasulfone combined with mesosulfuron/thiencarbazone alone or with pyrasulfotole/bromoxynil or bromoxynil controlled downy brome 98 to 99% compared to pyroxasulfone alone at 88%. In the greenhouse, Italian ryegrass was planted into dry conditions and sprayed with pyroxasulfone. Pots were irrigated with 0.3 inch of rainfall at 0, 8,15, 22,29, 36, and 43 DAT. Pots with untreated plants were included. The study is arranged as a randomized complete block with 4 replications. At all irrigation timings, no Italian ryegrass plants emerged.

Objective 2. Outcomes/Impacts: Pyroxasulfone (group 15) was registered for annual grass control, including Italian ryegrass and rattail fescue, in winter and spring wheat in spring 2014. Pyroxasulfone registration has aided in control of group 1 and 2 resistant Italian ryegrass. Very few herbicides control rattail fescue. Pyroxasulfone and pyroxasulfone/fluthiacet treatments controlled rattail fescue 89-97% in 2018. Winter wheat yield was not reduced by pyroxasulfone when 0.5 inch of sprinkler irrigation was applied immediately after planting and spraying on the same day (worst-case scenario). Wheat had minimal injury in 11 conventional-tilled (chisel plowed/field cultivated) sites and in seven direct-seed locations. U of I studies were instrumental in implementing pyroxasulfone label changes including an increased use rate and a preplant application time in winter wheat. These label changes have aided growers by giving them more options to improve weed efficacy. flufenacet also was registered in wheat fall 2014. Our flufenacet studies were useful to FMC when drafting rates and timings for their label. This information will help growers use these products safely and effectively to control grass weeds with minimal crop injury. These registrations provide needed tools to help control herbicide resistant weeds, especially Italian ryegrass.

Objective 3. Results: Three winter wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms October 2019. Pyroxasulfone, dimethenamid, and metolachlor were applied after seeding along with an untreated control. Experimental design was a split plot with herbicide as the main factor and variety with and without safener as the subfactor with four replications. Wheat will be harvested in August 2020. Spring wheat will be planted in 2020 in comparable experiment.

Objective 3. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide selection to increase herbicide rotations to combat resistance in the future.

Objective 4. Results: A field trial was re-established at UI research farms near Moscow and Genesee to examine tillage effects on rattail fescue. Spring wheat was direct seeded in 2019. The rotation is spring wheat- spring chickpea - winter wheat. Tillage initiated in the fall 2018 included fall disc or chisel plow followed by spring field cultivation. A no-tillage treatment is included as a control. Heavy harrow replaces disc in year 2 and 3. The tillage will be performed all 3 years, 2 years or 1 year for a total of 7 tillage regimes. In 2019, rattail fescue and brome density did not differ among treatments after the first tillage year. Tillage treatments were applied fall 2019 for the second year of the study. Chickpea will be planted spring 2020 and weed numbers and chickpea seed yield will be measured.

Objective 4. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control. Tillage is important but research on how invasive and how often is unknown. This data will help growers take an integrated weed management approach to reducing rattail fescue and increasing crop yield.

Objective 5. Two new broadleaf herbicides in winter wheat were evaluated. Halauxifen/fluroxypyr was evaluated for prickly lettuce and mayweed chamomile control in winter wheat. Halauxifen/fluroxypyr plus 2,4-D ester controlled prickly lettuce 90% at 80 DAT but did not control mayweed chamomile (79%). Bicyclopyrone/bromoxynil combined with various slow release fertilizers (NDemand 30L, Stand 12-0-2, Maximum N-Pact, CoRoN 28-0-0) did not visibly injure winter or reduce grain yield and test weight compared to the untreated check. Bicyclopyrone/bromoxynil was combined with grass herbicides (imazamox, pyroxsulam, and mesosulfuron/thiencarbazone) that require a urea ammonium nitrate (UAN) fertilizer adjuvant. The bicyclopyrone/bromoxynil label currently does not allow applications with fertilizer. Bicyclopyrone/bromoxynil alone plus UAN and imazamox plus bicyclopyrone/bromoxynil and UAN injured winter wheat 15%. Grain yield and test weight did not differ among treatments. Bicyclopyrone/bromoxynil applied at four growth stages (2 tiller, joint, swollen boot and ¼ head visible) did not visibly injured spring wheat. Grain yield did not differ among treatments including the untreated check. Aggressor herbicide controlled downy brome and feral rye 90% or better in Co-AXium winter wheat. Mesosulfuron/thiencarbazone controlled rattail fescue and suppressed jointed goatgrass.

Objective 5. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide resistant weeds. Bicyclopyrone/bromoxynil and halauxifen/fluroxypyr may be options for possible control of herbicide resistant broadleaf weeds.

Objective 6. Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage and rate. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. A ventenata sample was screened with 3 herbicides. It was resistant to mesosulfuron and sulfosulfuron (group 2) and susceptible to glyphosate. A jointed goatgrass sample was screened with 3 herbicides. It was resistant to imazamox (group 2) and susceptible to quizalofop and glyphosate. Seven downy brome seed samples were screened with 12 herbicides. No sample was resistant to metribuzin, pyroxasulfone, clethodim, sethoxydim, quizalofop or glyphosate. Samples were resistant to pyroxsulam, imazamox, propoxycarbazone, mesosulfuron, sulfosulfuron, and flucarbazone (group 2). Eight wild oat samples were screened with 9 herbicides. No sample was resistant to sethoxydim, clethodim or glyphosate. Samples were resistant to pyroxsulam, mesosulfuron, imazamox, and quizalofop. Some samples were developing resistance to pinoxaden and pinoxaden/fenoxaprop. A mayweed chamomile seed sample was treated with 4 herbicides. The sample was resistant to thifensulfuron/tribenuron and metsulfuron/thifensulfuron/tribenuron (group 2). It was not resistant to pyrasulfotole/bromoxynil and clopyralid/fluroxypyr.

Objective 6. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices.

Objective 7. Results: Project personnel participated in cereal schools in north Idaho in January. Research information was presented at the Western Society of Weed Science meeting in March. Cereal research was also presented at other grower meetings in the winter and field days in June and July.

Objective 7. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems.

OREGON REPORT

Research:

Control of kochia (Bassia scoparia), prickly lettuce (Lactuca serriola), and lambsquarter (Chenopodium berlandieri) in wheat. These weed species continue to be problematic and are widespread in the wheat cropping systems of the Pacific Northwest (PNW). The spread of Group 2 herbicide resistance in kochia and prickly lettuce in the region are probably the cause of many of the control problems. The objective of this research was to identify herbicide treatments with different modes of action for management of these species. The herbicides evaluated were three group 4 herbicides including fluroxypyr + halauxifen-methyl (6 fl oz/ac) , clopyralid + fluroxypyr (16 fl oz/ac), and 2,4-D (8 fl oz/ac); two group 2&4 herbicides including pyroxsulam + fluroxypyr (16 fl oz/ac) and florasulam + halauxifen-methyl (0.75 oz/ac); one group 6&27 herbicide containing bromoxynil + pyrasulfotole (13.5 fl oz/ac). A field study was conducted at the OSU Columbia Basin Agricultural Research Center near Pendleton, OR to test the efficacy of these herbicides against broadleaf weeds in spring wheat. The soil at this site is a Walla Walla silt loam. On April 17, 2019, ‘WB6341’ spring wheat was planted with a no-till drill with 10 in row spacing. Treatments were applied on May 31, 2019 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. Crop damage was not significant among treatments throughout the evaluation process. There were no significant differences among sprayed treatments for kochia control. The best results were obtained with pyroxsulam + fluroxypyr with 100% control. Prickly lettuce showed significant differences among treated plots. Bromoxynil + pyrasulfotole provided the best control (100%) followed by the tank mix clopyralid + fluroxypyr with halauxifen-methyl + florasulam (93%), clopyralid + fluroxypyr (88%), and the tank mix of fluroxypyr + halauxifen-methyl with 2,4-D (85%). Fluroxypyr + halauxifen-methyl alone and pyroxsulam + fluroxypyr had the lowest control with 34% and 43%, respectively. Lambsquarter’s control also showed significant differences among sprayed treatments. The tank mix of fluroxypyr + halauxifen-methyl with 2,4-D (100%), the tank mix of clopyralid + fluroxypyr with florasulam + halauxifen-methyl (100%), bromoxynil + pyrasulfotole (100%), and fluroxypyr + halauxifen-methyl (99%) had the highest control followed by pyroxsulam + fluroxypyr (91%) and clopyralid + fluroxypyr (84%).

Control of downy brome (Bromus tectorum L.) in winter wheat. Downy brome is probably the most problematic grassy weed in the wheat production systems of the PNW. Group 2 herbicide resistance is widespread in this species making its control sometimes impossible. It is urgent to find chemical options outside of Group 2 herbicides to control downy brome and preserve no-till agriculture. The objective of this research was to explore chemical options to control downy brome without relying only on group 2 herbicides. Two field studies were conducted at the OSU Columbia Basin Agricultural Research Center near Pendleton, OR. Experiment 1 was established to study the control of triallate (group 8), imazamox (group 2), pyroxsulam (group 2), and pyroxasulfone (group 15) and their combinations and experiment 2 was established to study the control of carfentrazone + pyroxasulfone (group 14+15), chlorsulfuron + metsulfuron methyl (group 2), metribuzin (group 5), propoxycarbazone (group 2), and their combinations. The soil at this site is a Walla Walla silt loam.

Experiment 1. On October 5, 2018, ‘ORCF 102’ winter wheat was planted with 10 in row spacing. Pre-plant incorporated treatment (triallate) was applied on October 4, 2018. Early post-emergence treatments were applied on November 15, 2018, delayed pre-emergence treatments (pyroxasulfone) were applied on October 30, 2018 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph and late post-emergence treatments were applied on April 24, 2019 using the same mentioned equipment. Downy brome control showed no significant differences among sprayed treatments due to the high variability in the data, ranging from a low of 55% with pyroxasulfone alone to a high of 96% with triallate + imazamox (LPOST) + NIS. Yield did not show any significant difference among treatments, ranging from a low of 57.03 bu/A with pyroxasulfone to a high of 74.40 bu/A with triallate + imazamox (LPOST) + NIS. Although no significant control differences were found, pre-emergence herbicides pyroxasulfone and triallate have shown to improve downy brome control and help to reduce downy brome group 2 resistant populations.

Experiment 2. On October 5, 2018, ‘Bobtail’ winter wheat was planted with 10 in row spacing. Treatments were applied with a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. Pre-plant treatments (carfentrazone + pyroxasulfone) were applied on October 4, 2018. Post-plant pre-emergence treatments (carfentrazone + pyroxasulfone with chlorsulfuron + metsulfuron methyl) were applied on October 12, 2018. Very early post treatments (metribuzin and metribuzin with carfentrazone + pyroxasulfone) were applied on November 15, 2018. The post-emergence treatment (propoxycarbazone) was applied on April 22, 2019. Significant differences were observed for downy brome control regarding treatments. Three treatments showed 100% control; carfentrazone + pyroxasulfone 3.5 fl oz/A (pre-plant), carfentrazone + pyroxasulfone 4.5 fl oz/A (pre-plant) and carfentrazone + pyroxasulfone 3.5 fl oz/ac (pre-plant) + carfentrazone + pyroxasulfone 1.0 fl oz/ac (very early post) + Metribuzin 2 oz/ac (very early post). However, these treatments were not different from carfentrazone + pyroxasulfone 2.5 fl oz/A (pre-plant) (82% control), carfentrazone + pyroxasulfone 3.5 oz/ac (post-plant pre-emergence) (75% control), carfentrazone + pyroxasulfone 4.5 oz/ac (post-plant pre-emergence) (76% control), and carfentrazone + pyroxasulfone 3.5 fl oz/ac (post-plant pre-emerge) + Olympus 0.9 oz/ac (very early post) (84% control). The least control was shown by carfentrazone + pyroxasulfone 2.75 fl oz/A (post-plant pre-emerge) (44%), carfentrazone + pyroxasulfone 3.5 fl oz/ac + chlorsulfuron + metsulfuron methyl 0.3 oz/ac (post-plant pre-emerge), carfentrazone + pyroxasulfone 3.5 fl oz/ac + Metribuzin 2 oz/ac (very early post), and with propoxycarbazone 0.9 oz/ac (post-emergence). I want to emphasize that the chemical control of downy brome could have been increased by competition with jointed goatgrass (Aegilops cylindrica) that was the prevalent weed in this trial.

The options for pre-emergence herbicides studied (triallate, pyroxasulfone, carfentrazone + pyroxasulfone) and metribuzin in post-emergence have been found to be good alternatives or complement to Group 2 herbicides for downy brome control.

Impacts: From an herbicide resistant strategy point of view, it is necessary to provide growers with as many tools as possible to control problematic weeds. This and the previous research provided some chemical options to control these problematic species and help growers make informed decisions.

Harvest weed seed control in wheat production systems of the PNW. Harvest weed seed control (HWSC) might perform an important role in controlling problematic weeds, by decreasing the weed seed bank. However, HWSC practices will not be effective if plants have previously shed all or a great part of their seeds before harvest, or if the combine is unable to collect the seed. The objectives of this study were: 1) evaluate the efficacy of chaff collection and chaff plus straw collection to reduce weed infestations and dispersion, 2) evaluate seed production, seed height, and seed retention of important weed species at harvest, and 3) determine the effects of chaff or chaff and straw removal on soil organic matter and moisture content. After two harvest seasons, in three studied farms, the collection of chaff did not produce significant differences in weed infestation compared to the control treatment (no residue removal). The collection of chaff and straw (bale direct system) provided marginally significant Sisymbrium altissimum reduction (10.6% on average) on one of the farms and a reduction tendency in the other farm with this problematic species. Bromus tectorum, Lolium perenne ssp. multiflorum, Vulpia myuros, and Chorispora tenella had an average seed retention at harvest of less than 50%. In addition, the low seed height in V. myuros and C. tenella makes these species poor candidates for HWSC. Sisymbrium altissimum and Secale cereale had average seed retention at harvest greater than 50% and seed height above 30 cm. The efficacy of HWSC practices in the PNW winter wheat cropping systems will be species dependent. While no differences have been found in soil carbon due to chaff or chaff and straw removal compared to the control, the collection of chaff plus straw caused a statistically significant reduction in gravimetric soil moisture (2 mm of precipitation per month) in the top 30 cm of soil. In arid and semi-arid areas, where the soil water accumulation is important, the removal of straw may not be a profitable practice.

Impact: We found that the efficacy of HWSC in the PNW is going to be species dependent and harvest time very critical to maximize control. The findings from this research will help growers in their decision to include these practices in their Integrated Weed Management programs depending on their weed issues and economy. These practices have a high potential to improve weed management in wheat production systems in our region, and consequently, their sustainability.

OKLAHOMA REPORT

Misha Manuchehri, Extension Weed Specialist, Department of Plant and Soil Sciences, Oklahoma State University, 371 Agricultural Hall, Stillwater, OK 74078. 405-744-9588. misha.manuchehri@okstate.edu

Identification and Management of ACCase Resistant Italian Ryegrass

Pinoxaden resistant Italian ryegrass biotypes were suspected in Oklahoma for many years; however, it wasn’t until last year that resistant populations were confirmed in greenhouse screenings. The use of group 15 herbicides may improve the control of these difficult-to-manage plants. Several studies have been conducted throughout Oklahoma over the past four years to evaluate the use of pyroxasulfone, pyroxasulfone + carfentrazone, and flufenacet+metribuzin on Italian ryegrass management. Control typically is > 90% for treatments that included pyroxasulfone at the delayed preemergence timing. Similar control is achieved with pyroxasulfone + carfentrazone and flufenacet + metribuzin but crop response from metribuzin often is seen; therefore, it is critical that proper rates are used for specific soil types. Timely rains and proper herbicide to soil contact also contributes to the success of these treatments. A current study is evaluating the impact of residue on the performance and crop response of these group 15 herbicides and preliminary results reveal the importance of proper seed bed prep when using mechanical tillage as well as good seed row closure.

Impact

Have screened thousands of weed biotypes in Oklahoma to aid weed managers in their decision making. From these screenings, we were the first to identify ACCase resistant Italian ryegrass in Oklahoma. With this information herbicide treatments that are not effective can be replaced with new plans that are. Successful ryegrass control can improve Oklahoma wheat yields by at least 20% and reduce grain discounts.

Winter Wheat Variety Tolerance to Metribuzin

Metribuzin is a herbicide that is still widely used in cropping systems annually. However, its use in winter wheat in Oklahoma has declined due to varietal sensitivity or lack of information regarding the topic. To evaluate modern winter wheat varieties, a trial was conducted at Dacoma, Fort Cobb, Goodwell, and Perkins, Oklahoma in the fall of 2019. Treatments consisted of two herbicide mixtures and a nontreated control. Mixtures included pyroxasulfone at 119 g ai ha^-1 plus 105 or 210 g ai ha^-1 of metribuzin. Herbicide mixtures were applied preemergence and delayed preemergence (wheat spike). Visual wheat response was recorded every two to three weeks after the first application. Six weeks after application at the Fort Cobb and Perkins locations, biomass from one meter of row was clipped at the soil surface, dried, and recorded. For biomass at Fort Cobb, there was an application timing by metribuzin rate interaction where biomass at the preemergence timing was 40 and 74% less than the nontreated control following metribuzin at 105 and 210 g ai ha^-1, respectively. At the delayed preemergence timing, biomass was similar following both rates but was reduced by approximately 31% compared to the nontreated control. For biomass at Perkins, there was a metribuzin rate effect where biomass decreased by 42% and 70% compared to the nontreated control following metribuzin at 105 and 210 g ai ha^-1, respectively. Results suggest that variety, application timing, and metribuzin rate will continue to be important when using this herbicide in wheat.

Impact

Approximately 86% of planted winter wheat acres in Oklahoma are public varieties. Increased information about varietal tolerance to metribuzin will improve relationships between Oklahoma agricultural stakeholders and Oklahoma State University. The use of metribuzin also will add a rarely used herbicide site of action to our list of management strategies to suppress and/or control winter annual grasses and will relieve some selection pressure for resistance from overused ALS and ACCase herbicides.

Rescuegrass Management in Winter Wheat

Rescuegrass is one of the most challenging winter annual weeds to manage in Oklahoma. There are few conventional herbicides labeled for rescuegrass control in winter wheat and for the ones that are labelled, control is often inconsistent. Products used in herbicide tolerant wheat (Clearfield® and CoAXium®) provide adequate control of rescuegrass; however, overreliance of these systems increases the selection pressure for herbicide resistant weed biotypes. To evaluate integrated management of rescuegrass, a study was conducted at Lahoma, Marshall, and Tipton, Oklahoma and Burkburnett, Texas to assess planting date, wheat variety, and herbicide selection on rescuegrass control. Wheat was planted at an optimal, delayed, and late timing where the early date represented the optimal time to sow wheat harvested for grain. Recently released varieties, Green Hammer and Showdown, were used. Both varieties offer high yield potential; however Showdown brings low competitive ability while Green Hammer offers high competition with advantage in forage yield. Two commonly used herbicides, pyroxsulam at 18.4 g ai ha^-1 and sulfosulfuron at 35.2 g ai ha^-1, were applied when rescuegrass was at the 2- to 3-leaf stage. At Lahoma, a delay in planting date increased percent visual weed control provided by the two herbicides. At Marshall, the same trend was observed; however, pyroxsulam controlled rescuegrass more than sulfosulfuron by 23%. Additionally, rescuegrass plants were counted for two 0.10 m^-2 quadrats per plot. Rescuegrass counts at Marshall decreased by 13 plants per 0.10 m^-2 from the optimal to delayed planting date. Overall, a delay in planting date did decrease rescuegrass populations while pyroxsulam and sulfosulfuron are two herbicide options for non-herbicide tolerant wheat that provided between 27 and 51% control in these studies.

Impact

Have shared identification and management tools for rescuegrass, a winter annual grass weed that is poorly understood in the state and beyond. Wheat fields infested with rescuegrass provide little grain and often are not worth investing chemical weed management dollars into as the plant is highly competitive and responds poorly to herbicides. Our data shares these facts with growers while encouraging them to manage the plant by rotating to a summer crop, using infested fields for primarily forage, or controlling rescuegrass with glyphosate or tillage prior to a delayed planting date.

UTAH REPORT

Research:

Kochia-cover crop study – Year 3 (2020)

The objective of this study is to evaluate the influence of cover crops, and planting dates and rates on kochia populations in wheat fields of Utah and southern Idaho. Similar to Years 1 (2018) and 2 (2019), planting dates and rates will be assessed as secondary tactics (e.g., early or late season plantings – avoidance, size advantage; high rates – resource use, competitive advantage) against kochia in combination with cover crops as a primary tactic.

Wheat allelopathy study – Year 2 (2020)

Many plants are reported to naturally produce secondary compounds that can have a deleterious effect on neighboring vegetation, also known as allelopathy. While not lethal, this allelopathic effect by a plant can also provide a competitive advantage against weed species. Unknown is to what extent allelopathy in wheat prohibits species of weeds. Therefore, our hypothesis is that wheat cultivars from the Pacific Northwest will stop weed species seed from germinating. The objective is to determine the allelopathic effect of several wheat cultivars on the growth and development of weed seed.

Extension:

Kochia-cover crop study – Year 3 (2020)

Similar to Years 1 (2018) and 2 (2019), specific methods for disseminating results will include: 1) establishing research at university field sites, 2) conducting field days in partnership with local growers, crop advisors and seed dealers (Utah Seed), 3) updating county educators, regional specialists, and private crop advisors at in-service meetings, 4) uploading findings on university extension and private organization websites, 5) presenting findings at local and regional meetings and conferences, 6) announcing project findings in local newsletters, newspapers for growers, and during statewide and regional speaking engagements, and 7) integrating research findings into course teachings that target next generation ag-professionals.

Impacts:

Kochia-cover crop study – Year 3 (2020)

Outcomes: Growers will benefit from our project through increased understanding and directly implementable results.

Kansas Report

Research:

Control of kochia (Bassia scoparia L.), Tansy mustard (Descurainia pinnata L.) and Henbit (Lamium amplexicaule L.) in winter wheat. Winter and summer annual broadleaf weed species, including tansy mustard, henbit, and kochia are problematic in Kansas winter wheat production. In addition, kochia has developed widespread resistance to ALS inhibitors (group 2) and glyphosate (group 9) herbicides in western Kansas. The purpose of this research was to determine the effectiveness of dichloprop-p (group 4), bromoxynil (Maestro^®, group 6), MCPA (Rhonox^®, group 4), and fluroxypyr (Comet^™, group 4) for control of kochia, tansy mustard, and henbit in winter wheat. All these herbicides were tested in different combination and application rates: dichloprop-p at 8, 12, 16 fl oz/a; Maestro^® at 16 and 24 fl oz/a; Rhonox at 4.5 and 9 fl oz/a; Comet at 7.5 and 11 fl oz/a. Field experiment was conducted at Kansas State University Agricultural Research Center in Hays, KS to test these treatments. Treatments were arranged in a randomized complete block design with 4 replications. Soil at the study site was Roxbury silt loam with pH 7.6 and 2.1% organic matter. Winter wheat variety “Joe” was drilled in tilled ground on Oct 3, 2018 at 10-in row spacing using seeding rate of 60 lbs/ac. Herbicide applications were made on April 15, 2019 when winter wheat was 4- to 5-tillers stages. Treatments were applied using a CO2-operated backpack sprayer set to deliver 14 gpa at 40 psi at 3.0 mph. At the time of herbicide applications, kochia was 2 to 3-in tall and, tansy mustard was 10 to 12 in tall and henbit was blooming. No significant crop injury was noticed with any of these tested treatments. Tank-mixed treatments of dichloprop-p + Maestro and dichloprop-p + Maestro + Rhonox at various rates provided effective control (88 to 96%) of tansy mustard and henbit at 45 days after treatments (DAT). Control of these two species ranged from 80 to 87% with sole treatments of dichloprop-p, Maestro, Rhonox, and Comet at 45 DAT. No significant differences were observed among treatments for kochia control and control ranged from 76 to 81% at 45 DAT. On an average, herbicide treatments improved wheat grain yield by 13 to 28% compared to non-treated weedy check plots.

Washington Report

Research:

Evaluation of Aggressor herbicide for the control of downy brome in the CoAXium wheat production system. The CoAXium™ wheat production system was recently developed by the Colorado Wheat Research Foundation, Inc., Limagrain Cereal Seeds, LLC and Albaugh, LLC. AXigen™ is the nonGMO trait in wheat that confers tolerance to the ACCase inhibitor (Group 1) herbicide Aggressor ™ (quizalofop-P-ethyl). The AXigen trait will be made available to both private and public breeders and was one of the reasons we were interested in evaluating the system. Aggressor is labelled to control annual grassy weeds, such as downy brome, jointed goatgrass and feral rye that are problematic in the low to intermediate rainfall zones of eastern WA. LCS Fusion AX winter wheat was direct seeded at the Cochran Farm near Walla Walla, WA. The soil at this site is a Ritzville silt loam. Postemergence treatments were applied on April 4th with a CO2-powered backpack sprayer set to deliver 15 gpa at 47 psi at 1.5 mph. The wheat growth stage was from 3 to 8 tiller and beginning to grow upright. Downy brome pressure was very high, with an average of 430 plants per square meter, and most of the plants were tillered. The level of downy brome control between the three rates of Aggressor evaulated was not significantly different. Downy brome control with Aggressor was not influenced by the addition of NIS, MVO or UAN. On the April 30th rating date, 26 days after application, all Aggressor treatments were providing greater than 95% control of downy brome. On the same rating date, Osprey and PowerFlex HL were providing approximately 50% control. On the final rating date, June 6th, all Aggressor treatments were providing outstanding control of downy brome, whereas Osprey and PowerFlex HL essentially were providing no control. Downy brome resistance to Group 2 herbicides like Osprey, PowerFlex HL, Beyond, and Outrider is common in the Walla Walla area. This trial demonstrated the effectiveness of the CoAXium Wheat Production System for the control of downy brome. However, overuse of this new technology is likely to quickly result in selection of downy brome biotypes resistant to the active ingredient, quizalofop-P.

Evaluation of Axial Bold for wild oat control in spring wheat. A field study was conducted near Pullman, WA to evaluate crop safety and wild oat control with Axial Bold. Axial Bold is a premixture of pinoxaden and fenoxaprop. Both active ingredients are ACCase inhibitors (Group 1). The study area followed winter wheat. Soil at this site is a Palouse silt loam with 4.2% organic matter and a pH of 5.0. On May 28th, treatments were applied with a CO2-powered backpack sprayer set to deliver 10 gpa at 49 psi at 2.3 mph. Wheat was at the two tiller stage and was 12 inches tall. Wild oat plants were 3 inches tall and there were an average of 12 plants per square meter.In general, group 1 herbicides including Axial Bold, Axial XL, Tacoma 1EC and Discover NG, provided better control than group 2 herbicides including Everest 3.0, Olympus and OpenSky. None of the treatments provided commercially acceptable (> 80%) control. Axial Bold was the only treatment to come close to this level of control. Olympus- and OpenSky-treated plots yielded similarly to the nontreated check plots. Yield was increased by all other treatments when compared to the nontreated check. No crop injury was observed with any of the treatments in this study. Some wild oat populations in Washington, including the population in this study, are now resistant to Axial. Axial has helped to keep wild oat under control for many years, but as this study demonstrates, our ability to control wild oat with Axial is diminishing. The addition of fenoxaprop to pinoxaden (Axial Bold) provides some additional control of wild oat, but it may be insufficient for the control of populations already resistant to Axial.

Germination response of downy brome, wild oat, and Italian ryegrass to gibberellic acid in Palouse silt loam. Downy brome (Bromus tectorum L.), Italian ryegrass (Lolium multiflorium) and wild oat (Avena fatua L.) currently plague the dryland wheat production systems of the Pacific Northwest (PNW). Each of these grass species dominate in distinct climatic zones. Downy brome, a winter annual, is common in the low to intermediate rainfall zones. Italian ryegrass also a winter annual, and wild oat, a summer annual, invades in high rainfall zones. Gibberellic acid (GA3), is a naturally occurring plant growth hormone that can be used alleviate seed dormancy, as well as modifying flowering, germination, and senescence processes. A greenhouse study was conducted to access the response of new and old seed of the three grass species to GA3 (RyzUp Smartgrass) in Palouse Silt Loam soil. Treatments of GA3 (1.4, 14, 28, 56 g ai ha -1) were applied to the prepared soil surface and immediately incorporated with approximately 0.25 cm of water. A negative control (0 g ai ha-1) and a positive control (GA3 soak) were included. Seedling germination was assessed at 1, 2, and 3 WAT. At 4 WAT final counts were recorded, and aboveground biomass was harvested. Treatment and age of seed significantly (P <0.001) affected the response downy brome counts 4 WAT. Italian ryegrass counts at 4 WAT were significantly (P <.0150) impacted by both treatment number and age of seed. Wild oat germination was not affected by GA3 applications, but by age of seed - older seed resulted in more plants than new seed. Based on this data, GA3 could be used as an effective management tool for newly seeded downy brome and Italian ryegrass seedbanks in dryland wheat production systems of the PNW.

Barroso, J., D.J. Lyon, and T. Prather. 2019. Russian thistle management in a wheat-fallow crop rotation. (PNW492).

Beaudoin, M. R., R. J. Zuger, and I. C. Burke. 2020. Germination response of downy brome, wild oat, and Italian ryegrass       to gibberellic acid in Palouse silt loam. Weed Sci. Soc. Am. Abst 60:160.

Lyon, D.J., M.E. Thorne, P. Jha, V. Kumar, and T. Waters. 2019. Volunteer buckwheat control in wheat. Crop Forage    Turfgrass Manage. doi:10.2134/cftm2019.05.0033.

Kerbs, B.D., A.G. Hulting, and D.J. Lyon. 2019. Scouringrush (Equisetum spp.) control in dryland winter wheat. Weed       Technol. 33:808-814.

Lyon, D. J, Walsh, M. J., Barroso, J, Campbell J. M., and A. G. Hulting. 2019. Harvest Weed Seed Control:   Applications for PNW Wheat Production Systems. PNW 730. p. 10.

Raiyemo, D. A., J. M. Campbell, R. Ma, W. J. Price, T. A. Rauch, and T. S. Prather. 2019. Safener may enhance   tolerance to soil-applied herbicide for winter wheat varieties grown in the Pacific Northwest. Weed        Science Society of America Proceedings. http://wssaabstracts.com/public/59/proceedings.html.

Rauch, T., and J. Campbell. 2019. Broadleaf weed control in wheat with halauxifen plus florasulam. Western       Society of Weed Science Proceedings 72:30.

Kumar, V., R. Liu, and D.E. Peterson. 2019. Management of feral rye with CoAXium wheat production system       in Kansas. K-State Agronomy eUpdates (published on Oct 11, 2019). https://webapp.agron.ksu.edu/agr_social/article_new/management-of-feral-rye-with-coaxium-wheat-     production-system-in-kansas-357