Brief Summary of Minutes of Annual Meeting

Project No. and Title: WERA-77

Managing Invasive Weeds in Wheat
Period Covered: 10-2019 to 09-2020
Date of Report: 04/17/2021
Annual Meeting Dates: 03-01-2020 to 03-04-2020

Selection of New Secretary/Chair Elect:

Lovreet Shergill volunteered to be the new secretary/chair elect for next year. All the meeting participants agreed. Consequently, next year (2022) Caio Brunharo will organize and conduct the meeting and Lovreet Shergill will take notes and file the annual report.

The meeting was conducted on March 1, 8-9am.

Kansas Report Vipan Kumar Research:
Evaluation of Anthem Flex application timings for downy brome (Bromus tectorum) and blue mustard (Chorispora tenella) control in winter wheat. A field study was conducted at Kansas State University Agricultural Research Center near Hays, KS in 2019/2020 growing season to determine the effectiveness of Anthem Flex herbicide rates and application timings for control of downy brome and blue mustard. Study site was planted with a winter wheat variety ‘Joe’ on Oct 3, 2019 using 60 lbs/a seeding rate. The study evaluated Anthem Flex at 2.5, 3.25, and 3.5 fl oz/a as preplant and preemergence (PRE) timings as well as in sequential application at 3.25 fl oz/a followed by a POST application of Olympus at 0.6 oz/a. In addition, a tank-mixture of Anthem Flex at 2.8 fl oz/a plus Finesse at 0.4 oz/a applied delayed PRE (DPRE) was also tested.

Herbicide treatments for preplant, PRE, DPRE and POST timings were applied on Sep 29, Oct 7, Oct 11 and Nov 19, 2019, respectively. All treatments were applied with a CO2-operated backpack sprayer set to deliver 14 GPA at 35 psi at 3 mph. The study site had natural infestation of downy brome and blue mustard. Data on winter wheat injury, percent visible control of downy brome and blue mustard were collected. No visual injury on winter wheat was observed with Anthem Flex treatments tested across all rates and timings. Irrespective of application timing and rates, all Anthem Flex treatments provided excellent, late-season control of downy brome (92 to 99%) and blue mustard (95 to 99%) compared to non-treated plots. Reduced interference of downy brome and blue mustard by Anthem Flex-based treatments resulted in wheat grain yields of 50 to 60 bu/a, as compared to nontreated plots (18 bu/a). In conclusion, these results suggest that the Anthem Flex applied at 2.5 to 3.5 fl oz/a rate in preplant, PRE, or delayed PRE timings can provide an effective control of downy brome and blue mustard in dryland winter wheat in western Kansas.

Response of feral rye (Secale cereal L.) populations from Kansas wheat fields to Aggressor™ and Beyond® herbicides. Feral rye is one of the most troublesome winter annual grass weed species in Kansas winter wheat production. Two herbicide-tolerant wheat production systems, viz. CoAXium® winter wheat (resistant to quizalofop-p-ethyl) and Clearfield® winter wheat (resistant to imazamox) are currently available for selective control of winter annual grass weed species, including feral rye. However, there is lack of information on the response of feral rye populations from Kansas wheat fields to Beyond® (imazamox) and Aggressor™ (quizalofop) herbicides. Seeds of about eight different feral rye populations were collected in 2020 from four different counties in north central Kansas at the time of wheat harvest. Greenhouse experiments were conducted at Kansas State University Agricultural Research Center in Hays, KS, to determine the response of those populations to increasing doses of Beyond® and Aggressor™ herbicides. Feral seedlings from each population were grown in 4-inch squared plastic pots containing commercial potting mixture. Experiments were conducted in randomized complete block (blocked by population) design with 12 replications. Beyond® herbicide doses of 0, 1.25, 2.5, 5, 10, and 20 fl oz/a and Aggressor™ herbicide doses of 0, 2, 4, 8, 16, and 32 fl oz/a were separately tested on each feral rye population. All Beyond® doses included methylated seed oil (MSO) at 1% v/v and Aggressor™ doses included nonionic surfactant (NIS) at 0.25% v/v. All herbicide doses were applied when feral rye seedlings reached 2 to 4-lf stage in a cabinet spray chamber. Data on shoot dry weights were collected at 21 days after treatment (DAT) and analyzed using 3-parameter log-logistic model in R software. Based on dose-response analysis, the estimated GR90 values for Beyond® herbicide (the dose needed for 90% reduction in shoot dry weights) ranged from 8.2 to 41.4 fl oz/a (wide variation in response to Beyond® herbicide); whereas, the estimated GR90 values for Aggressor™ herbicide ranged from 7.5 to 14.7 fl oz/a among the tested populations. Based on these results, it can be concluded that the tested feral rye populations will not be controlled with the labelled field-use rate of Beyond® herbicide (5 fl oz/a), but should be controlled by a field-use rate (10 to 12 fl oz/a) of Aggressor™ herbicide.

Impact Statement: These research findings were shared with Kansas wheat growers through a numerous presentations and popular press articles on Kansas Agricultural Experiment Station Research Reports (https://newprairiepress.org/kaesrr/vol6/iss5/23/). Results were also shared with wheat growers, county ag agents and crop consultants through Weed Schools, Crop Pest Management Webinar, and Cover Your Acres conference conducted across western Kansas in fall of 2020 or spring 2021.

Washington Report

Drew J. Lyon and Ian C. Burke
Research:
Evaluation of Avadex® Microactiv™ herbicide for the control of downy brome and Italian ryegrass. The objectives of this study were twofold: 1) Determine the level of control that Avadex MicroActiv (Group 8) provides against downy brome and Italian ryegrass in a direct seed winter wheat production system, and 2) Ascertain if the combination of Avadex MicroActiv with either Zidua (Group 15), Zidua + Sencor (Group 5), Beyond (Group 2) or PowerFlex HL (Group 2) provides better grass weed control than the products applied individually. The soil at this site is an Athena silt loam with 2.9% organic matter and a pH of 5.2. Winter wheat was the previous crop. The field was sprayed with glyphosate on October 6, 2019 and Avadex MicroActiv was applied with a 50 ft Valmar applicator on October 7th at 15 lb/A to half of the trial area. Two, 50 ft by 200 ft strips received Avadex MicroActiv and two strips did not.

Herbicide treatments were randomized and replicated four times within the respective strips. On October 8th, the trial area received 0.47 inch of rainfall that aided in the activation and incorporation of the Avadex MicroActiv. Mechanical incorporation of the Avadex MicroActiv occurred at planting on October 10th with a Horsch high disturbance direct-seed drill with paired rows on a 15-inch row spacing. The cultivar UI Magic CL+ was seeded at a depth of 1.5 inches and a rate of 110 lb seed/acre. Zidua and Zidua + Sencor preemergence treatments were applied on October 11th with a CO2-powered backpack sprayer. Beyond and PowerFlex HL were applied postemergence in the fall (November 18, 2019) and in the late winter (February 28, 2020). On November 18, 2019 there was an average of 24 annual grass plants per square foot in the four, nontreated check plots. None of the herbicides applied caused any crop injury. Avadex MicroActiv and Zidua each provided some control of downy brome and Italian ryegrass. Avadex MicroActiv provided slightly better downy brome control, whereas Zidua provided slightly better Italian ryegrass control. Neither product provided commercially acceptable control of either annual grass weed when applied alone. The combination of Avadex MicroActiv plus Zidua provided the best control of downy brome and Italian rygrass and increased yield by 18 bu/A when compared to the nontreated check. The addition of Sencor to Zidua did not increase the control of either annual grass weed when compared to Zidua alone or in combination with Avadex MicroActiv. The group 2 herbicides (Beyond and PowerFlex HL) provided very little control of either downy brome or Italian ryegrass when applied on their own. However, when combining Beyond or PowerFlex HL with Avadex MicroActiv, downy brome control was better than Italian ryegrass control. This study demonstrated that as resistance to the postemergence Group 2 herbicides increases in both downy brome and Italian ryegrass, it will be important to use preplant and preemergence herbicides with at least two different sites of action to control these two troublesome annual grass weeds in wheat.

Management of downy brome in the Pacific Northwest (PNW) has become more challenging due to the emergence of triazine, ALS-inhibitor, ACCase-inhibitor and glyphosate resistant genotypes. One potential method to manage herbicide resistant downy brome would be evolutionary theory-based methods aiming to reduce the reproductive fitness of downy brome by changing the cropping systems sufficiently to select against the various genotypes known to be present in the PNW. To develop evolutionary based methods, we must know how much adaptive traits vary across the region and within fields so the potential response to evolutionary management methods can be modeled. Full-Sib families were grown in two greenhouses with 3 replications in each greenhouse, after 53 days of vernalization. Number of tillers, height (cm), days until visible panicle, and days until first ripe seed were measured. The percent of total variability explained by a trait was calculated using mixed models to perform an analysis of variance. The percent of the phenotypic variability explained by the Full-sib families varied by trait ranging from 24.1% for days to first ripe seed to 80.3% for first visible panicle. Number of tillers and height, both traits thought to be plastic had 65.2% and 32.5%. The only large effect that was not attributed to the full-sib families was the height trait, where it accounted for 28.2% of the total variation present. The Full-sib Family was a significant random effect in all traits.

Because large amounts of heritable variation in adaptive traits is present, it is likely that genotype by location interactions could maintain genetic variation if migration is present. Reducing migration of downy brome seed may limit the amount of genetic/phenotypic adaptation within fields thus the effectiveness of alternative management methods such as mowing or crop rotation may be improved. Equipment shared between fields/locations should be cleaned thoroughly after use to prevent the maintenance of genetic/phenotypic variation in downy brome in PNW wheat.

Impact Statement: Grower and industry awareness of herbicide resistance continued to increase in 2020 through a variety of presentations and articles in the popular press and through Timely Topic posts, the Weeders of the West Blog, and WSU Wheat Beat Podcast episodes on the Wheat and Small Grains Website (smallgrains.wsu.edu). Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

IDAHO REPORT

Joan Campbell Research:
Objective 1. Results. A study established in the fall 2019 in CoAXium ‘Fusion’ winter wheat examined a possible interaction between Aggressor (quizalofop) herbicide application timing and eyespot disease. No disease was present this year. Lodging occurred from late applications timings of Aggressor (2 node stage which is off label).

Objective 1. Outcomes/Impacts. Understanding the CoAXium system helps aid our growers to obtain the highest grain quality and yield while also controlling difficult annual grass weeds.

Objective 2. Results. A winter wheat/Italian ryegrass control study evaluated pyroxasulfone and pyroxasulfone/carfentrazone at the highest labeled rates with the following application times: pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat.
Italian ryegrass control at the pre-fertilization timing was less than all other application timings. Italian ryegrass control was improved with pyroxasulfone/carfentrazone versus pyroxasulfone at all timings due to a higher rate of pyroxasulfone. Axiom did not control Italian ryegrass and is most likely due to a resistant population. This study is being repeated in 2021.

In other trials, pyroxasulfone combined with mesosulfuron/thiencarbazone alone or with pyrosulfotole/bromoxynil controlled downy brome 89 to 92% compared to pyroxasulfone alone at 76%. Pyroxasulfone/flumioxazin or pyroxasulfone/flumioxazin/metribuzin controlled downy brome 90% or better and did not injure winter wheat.

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 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. Pyroxasulfone/carfentrazone also was registered in wheat fall 2014. Our pyroxasulfone/carfentrazone 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: Castle CL, Magic CL, and Sparrow 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. dimethenamid and metolachlor herbicides applied at a 3X rate postplant preemergence caused substantial injury and yield reduction to Sparrow and Magic CL winter wheat varieties at one location. Yield was increased with safener. Castle CL showed a level of inherent tolerance. Pyroxasulfone applied at a 3X rate did not cause visual injury at either location. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms spring 2020. 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.
No spring wheat variety was visibly injured by dimethenamid, metolachlor or Pyroxasulfone at a 2X rate applied postplant preemergence at two locations. Metolachlor and dimethenamid resulted in a 5 to 7% yield reduction.

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, windgrass 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 mode of action to aid herbicide resistant weed management in wheat.

Objective 4. 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 to control Italian ryegrass. Untreated plants are included from each sample. Due to limited greenhouse space, samples screenings are in progress for pyroxasulfone, metolachlor, dimethenamid and Axiom. No sample is resistant to pyroxasulfone or glyphosate. Pinoxaden resistance is 74% while pyroxsulam and mesosulfuron resistance is widespread 89 and 90%, respectively. The non-selective group 1 herbicides with resistance includes: clethodim (23%) < sethoxydim (57%) < quizalofop (77%).

Objective 4. 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 5. Results: A field trial was re-established at UI research farms near Moscow and Genesee to examine tillage effects on rattail fescue. Chickpea was direct-seeded spring 2020. 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 is performed all 3 years, 2 years or 1 year for a total of 7 tillage regimes. In 2020, rattail fescue in chickpea was higher in the direct seed treatment. Winter wheat was planted fall 2020 and weed numbers and wheat yield will be measured.

Objective 5. 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 in direct seed. 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 6. Results: Three new broadleaf herbicides in winter wheat were evaluated. pyrosulfotole/bromoxynil FX (pyrasulfotole/bromoxynil/fluroxypyr) and WideARmatch (fluroxypyr/clopyralid/halauxifen) provide good mayweed chamomile control at 95 and 99%, respectively. Pixxaro (fluroxypyr/halauxifen) plus 2,4-D also controlled mayweed chamomile 94% at 70 DAT. Talinor applied to winter wheat combined with mesosulfuron/thiencarbazone and fungicides did not reduce yield compared to the untreated check.

Objective 6. 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. Talinor, WideARmatch, and Pixxaro may be options for possible control of herbicide resistant broadleaf weeds.

Objective 7. Results: 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. 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. Three interrupted windgrass samples were screened to 5 herbicides. All samples were resistant to imazamox, mesosulfuron, pyroxsulam (group 2) and susceptible to pyroxasulfone and glyphosate. Two downy brome seed samples were screened with 8 herbicides. Samples were susceptible to metribuzin, pyroxasulfone, quizalofop or glyphosate. Samples were resistant to pyroxsulam, imazamox, propoxycarbazone, and mesosulfuron (group 2). A kochia sample was screened to 5 herbicides. It was susceptible to saflufenacil, dicamba, fluroxypyr, and glyphosate and was resistant to imazamox (group 2).

Objective 7. 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 8. Results: Project personnel participated in cereal schools in north Idaho in January. Research information was presented at the Weed Science Society of America/Western Society of Weed Science joint meetings in March. Cereal research was also presented at other grower meetings in February and in-person field day in June.

Objective 8. 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.

OKLAHOMA REPORT

Misha Manuchehri Research:
Tillage System Impact on Efficacy of Delayed Preemergence Herbicides in Winter Wheat.

Delayed PRE herbicides can provide season-long Italian ryegrass (Lolium perenne L. ssp.
multiflorum (Lam.) Husnot) control in Oklahoma winter wheat when applied at proper rates and successfully incorporated. However, heavy previous crop residue found in reduced tillage systems may reduce efficacy. Some herbicide labels describe this, and producer sentiments echo it. A study was conducted during the 2019-20 and 2020-21 seasons near Stillwater, Oklahoma to evaluate the efficacy of delayed PRE herbicides in no-till, conservation, and conventional wheat tillage systems. Conservation tillage was comprised of a single pass of a sweep plow set approximately 10 cm below the soil surface with a rotary hoe following behind. The conventional tillage system was disked twice with a tandem disk prior to planting. Plots were maintained weed free throughout the summer fallow period with burndown herbicide applications as needed. Herbicide treatments consisted of metribuzin, pinoxaden, pyroxasulfone, and/or pyroxasulfone + carfentrazone-ethyl applied alone or in tank-mixture. No tillage by herbicide interaction was observed for visual crop injury, weed control, or wheat yield.

Significant crop injury for pyroxasulfone + metribuzin was observed in 2019. No visual crop injury was noted in 2020, likely due to delayed rains. In both years, ryegrass control greater than 92% was achieved following treatments of pyroxasulfone + metribuzin and pyroxasulfone + pinoxaden. Soil surface residue as influenced by tillage did not affect the efficacy of delayed PRE herbicides in winter wheat. With a wide range of tillage systems across Oklahoma, these results may influence use of PRE herbicides moving forward.

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 Fort Cobb and Perkins, Oklahoma in the fall of 2019. Winter wheat varieties Fusion AX, Showdown, Strad CL Plus, and Uncharted were evaluated. Treatments consisted of two herbicide tank 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 PRE or delayed PRE (wheat spike). Visual wheat response, biomass, and crop yield were recorded. For biomass collected between 4 and 6 weeks after planting at Fort Cobb and Perkins, there was a metribuzin rate main effect where compared to the nontreated control, biomass decreased by 40% and 42% at 105 g ai ha-1 and 74% and 70% at 210 g ai ha-1, respectively. Fort Cobb derived a time by rate interaction for yield where the high rate applied PRE displayed reduction. For Perkins, a yield by rate by variety interaction occurred where Strad CL Plus showed a significant reduction between all treatments, Fusion AX and Uncharted showed a yield reduction at the high rate, and Showdown exhibited no yield reduction across all treatments.

Results suggest that proper application rate in accordance to soil type and characteristics is important, crop application timing is crucial, and variety tolerant selection is imperative.

Rescuegrass Management in Winter Wheat. Rescuegrass (Bromus catharticus) is an early emerging winter annual grass weed prevalent in winter wheat production of the southern Great Plains. Growers can successfully manage rescuegrass in herbicide tolerant wheat systems; however, control in non-herbicide tolerant wheat often is poor. To evaluate integrated management of rescuegrass and other Bromus spp., a study was conducted at Marshall and Lahoma, Oklahoma and Burkburnett, Texas to assess an early, mid-, and late planting date, one high-competitive and one low-competitive wheat variety, and two common herbicides: sulfosulfuron at 35.2 g ai ha-1 and pyroxsulam at 18.4 g ai ha-1. The earliest date represented optimal sowing window for grain only wheat production. At Marshall, mid- and late planting dates decreased rescuegrass biomass 19 and 23 g per 0.25 m-2, respectively, compared to the early planting date. At Burkburnett, a reduction in downy brome (Bromus tectorum) biomass was observed for the late planting date, reducing biomass by 28 and 37.6 g more than mid or early date, respectively. Pyroxsulam controlled rescuegrass best at Marshall by decreasing biomass 28 g more than sulfosulfuron. Although, sulfosulfuron had better control at Burkburnett by decreasing rescuegrass biomass 5.5 g more than nontreated. True cheat (Bromus secalinus L.) and downy brome biomass decreased 98% after both pyroxsulam and sulfosulfuron treatments at Lahoma. Treatments of pyroxsulam or sulfosulfuron and a delay in planting by two to six weeks after the early sowing time did provide a reduction in rescuegrass biomass.

Impacts

Group 15 herbicides are currently the only chemical tool to manage Italian ryegrass in Oklahoma winter wheat. According to our research, when using a carrier volume of at least 15 gallons per acre, tillage system, likely will not impact ryegrass control.

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.

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.

OREGON REPORT

Judit Barroso Research:
Control of prickly lettuce (Lactuca serriola) and lambsquarter (Chenopodium berlandieri) in spring wheat. In a continuing effort to find herbicides with different modes of action active on problem species, such as prickly lettuce and lambsquarter in wheat, we conducted this experiment at the Columbia Basin Agricultural Research Center in 2020. The herbicides tested were pre-tank mixes of fluroxypyr + halauxifen-methyl (both group 4), fluroxypyr + clopyralid + halauxifen-methyl (all group 4), fluroxypyr + pyroxsulam (groups 4 and 2), bromoxynil + pyrasulfotole (groups 6 and 27), and tank mixes of fluroxypyr + halauxifen-methyl with 2, 4-D (group 4), fluroxypyr + halauxifen-methyl with and thifensulfuron-methyl (group 2), fluroxypyr + clopyralid + halauxifen-methyl with 2,4-D, fluroxypyr + clopyralid + halauxifen-methyl with thifensulfuron-methyl, and fluroxypyr + clopyralid with halauxifen-methyl + florasulam (groups 4 and 2). The experiment was a complete randomization block design with four repetitions. The crop was seeded with a conventional drill with 7.5 inch row spacing. Treatments were applied on May 27, 2020 using a CO2-powered backpack sprayer set to deliver 15 gpa at 40 psi at 3.1 mph. The wheat ranged from 2-5 tillers to in the boot stage and was 2 feet tall at the time of application. Prickly lettuce was 7-9 leaves and 5-10 inches tall. Lambsquarter was 4-10 shoots and 4-12 inches tall. Weed control was evaluated at two, six, and eight weeks after treatment using a visual evaluation from 0 to 100, with zero indicating no control and 100 complete control. Prickly lettuce showed significant differences among treated plots for all three evaluation dates. On the final evaluation date, fluroxypyr + clopyralid + halauxifen-methyl with 2,4-D and bromoxynil + pyrasulfotole had the highest control at 100%, which was not significantly different from fluroxypyr + clopyralid + halauxifen-methyl with thifensulfuron- methyl, fluroxypyr + clopyralid with halauxifen-methyl + florasulam, fluroxypyr + clopyralid + halauxifen-methyl, fluroxypyr + halauxifen-methyl with 2, 4-D with a control higher than 96%. Fluroxypyr + clopyralid with thifensulfuron-methyl and fluroxypyr + pyroxsulam show slightly lower control but close to 90% and fluroxypyr + clopyralid showed the least control at 84%.

Lambsquarter did not show significant differences among sprayed treatments on any of the three evaluation dates, ranging from 99-100% control.

Impacts: We are providing growers with information on prickly lettuce and lambsquarter control using herbicides with different modes of action (MOA). This study will help them to design integrated weed control strategies that prevent the development of resistant populations.

Improve Russian thistle (Salsola tragus) management in wheat cropping systems.

a) Effect of row spacing and seeding rate on Russian thistle in spring barley and spring wheat.
Russian thistle is a persistent post-harvest issue in the semi-arid region of Pacific Northwest (PNW). Farmers need more integrated management strategies to control it. Russian thistle emergence, mortality, plant biomass, seed production, and crop yield were evaluated in spring wheat and spring barley planted in 18- or 36-cm row spacing and seeded at 73 or 140 kg ha−1 in Pendleton and Moro, Oregon, during 2018 and 2019. Russian thistle emergence was lower, and mortality was higher in spring barley than in spring wheat. However, little to no effect of row spacing or seeding rate was observed on Russian thistle emergence or mortality in both years. Russian thistle seed production and plant biomass followed crop productivity; higher crop yield produced higher Russian thistle biomass and seed production and lower crop yield produced lower weed biomass and seed production. Crop yield with Russian thistle pressure was improved in 2018 with 18-cm rows or by seeding at 140 kg ha−1 while no effect was observed in 2019.

Increasing seeding rates or planting spring crops in narrow rows may be effective at increasing yield in low rainfall years of the PNW, such as in 2018. No effect may be observed in years with higher rainfall than normal, such as in 2019.

Impacts: A good crop is necessary to suppress Russian thistle germination and reduce its density during the growing season. Spring barley has shown to be more competitive than spring wheat to suppress Russian thistle. In the semi-arid region of the PNW, including spring barley over spring wheat is recommended to suppress Russian thistle. Increasing seeding rates or planting spring crops in narrow rows may be effective in low rainfall years but no effect may be observed in years with higher rainfall than normal.

a) Evaluation of different herbicides and adjuvants, and application time to improve post- harvest Russian thistle chemical control. Two trials, one in Pendleton, OR and one in Moro, OR, were established to evaluate several post-emergence herbicides with different adjuvant options (Tables 1) to control Russian thistle in fallow and post-harvest. The herbicides studied were Gly Star® Plus (glyphosate), Sharpen® (saflufenacil), Deadbolt® (bromoxynil + 2,4-D), Brox®-M (bromoxynil), Huskie® (bromoxynil + pyrosulfotole) and Starane® NXT (bromoxynil + fluroxypyr). The adjuvants studied were In-Place® (Drift control agent), Fire-Zone® (Methylated Seed Oil (MSO)), ExuroTM (MSO), Accudrop® (Drift control agent + deposition aid + surfactant), and Hell-Fire®(Herbicide activator). Russian thistle seeds were sprinkled in the experimental area right before seeding to secure a uniform infestation. The trials were a split-plot complete randomized block design with four repetitions, where the main plot (10 ft x 40 ft) was the chemical treatment and the sub-plot (10 ft x 20 ft) was the application time (in the first 2 days after harvest (DAH) and in two weeks after harvest (WAT)). Treatments were conducted with a CO2-powered backpack sprayer delivering 15 gal/A. Visual weed control assessments were performed 3 and 6 weeks after treatment (WAT) to evaluate herbicide and adjuvant efficacy. In both sites, treatments improved Russian thistle control when they were sprayed 2 WAH compared to 2 DAH (Table 1). This may be due to the plants having extra time to regrow after harvest, therefore having more surface area to be treated and/or growing more actively. Gly Star Plus treatments and Huskie treatment were least affected by the spray time. There was not significant difference among the adjuvants applied with Gly Star Plus or Sharpen.

In Pendleton, on the final evaluation date for the 2 DAH application, all four Gly Star Plus treatments, as well as the Huskie treatment, showed Russian thistle control of 94-100%. The remaining treatments, including all Sharpen treatments, Deadbolt, Brox-M, and Starane NXT, showed varying degrees of significant difference ranging from 53-100%. On the final evaluation date for the application at 2 WAH, all Sharpen treatments, Deadbolt, and Starane NXT treatments showed similar control to Gly Star Plus and Huskie treatments. Brox-M showed the lowest Russian thistle control among sprayed treatments.
In Moro, on the final evaluation date for the 2 DAH application, all treatments showed similar control (82%-99%), except Sharpen + 2,4-D, Deadbolt and Brox-M, which showed lower effect ranging from 79% to 51%. On the final evaluation date, for the 2WAT application, the control increased for all treatments, with Sharpen + 2,4-D, Brox-M, and Starane NXT showing the lowest control ranging from 87% to 86%. All treatments, except for the mentioned three, showed controls higher than 90%. Sharpen showed the need for an MSO adjuvant, the control with Sharpen + MSO was always higher that with the tank-mix Sharpen + 2,4-D, as it can be observed in the Pendleton trial as well.

Impacts: We have observed higher herbicide control 2 WAH than 2DAH, indicating that growers have some time after harvest to control Russian thistle adequately, in fact they should not stop harvesting to control this weed. The use of best herbicide + adjuvant combination is herbicide- adjuvant specific. Saflufenacil plus an MSO adjuvant and bromoxynil products have shown to be good alternatives to control Russian thistle in fallow or post-harvest to glyphosate. Glyphosate effect was improved with the adjuvant Hel-Fire®.

Table 3. Weed control (%) at six weeks after treatment (WAT) of Russian thistle for the different treatments at 2 days after harvest (DAH) and 2 weeks after harvest (WAH) in Pendleton, OR and in Moro, OR in 2019.  SEE ATTACHMENT FOR TALBE 3.

Research Publications:

Adhikari, S., I. C. Burke, and S. D. Eigenbrode. 2020. Mayweed chamomile (Anthemis cotula L.) biology and management – a review of an emerging global invader. Weed Research 60:313- 322.
Burke, T. L., and I. C. Burke. 2020. Vernalization affects absorption and translocation of clopyralid and aminopyralid in rush skeletonweed (Chondrillaq juncea). Weed Sci. 68:445-450. Fischer, J.W., M.E. Thorne, and D.J. Lyon. 2020. Weed-sensing technology modifies fallow control of rush skeletonweed (Chondrilla juncea). Weed Technol. 34:857-862. doi.org/10.1017/wet.2020.76.
Kumar V, Liu R, Manuchehri MR, Westra EP, Gaines TA, Shelton CW (2021) Feral rye control in quizalofop-resistant wheat in central Great Plains. Agron J. DOI: 10.1002/agj2.20484 Manuchehri, M. R., E. P. Fuerst, S. O. Guy, B. Shafii, D. L. Pittmann, and I. C. Burke. 2020.
Growth and development of spring crops in competition with oat in the dryland Mediterranean climate of eastern Washington. Weed Science 68: 646-653.
Raiyemo, D. A., W. J. Price, T. A. Rauch, J.M. Campbell, F. Xiao, R. Ma and T. S. Prather. 2020. A Safener Does Influence Pacific Northwest Winter Wheat Varietal Response to Very-Long-Chain Fatty Acid-Inhibiting Herbicides. Western Society of Weed Science Proceedings 73:323.
Raiyemo, D., Price, W., Rauch, T., Campbell, J., Xiao, F., Ma, R., Gross, R. Prather, T. (2020).

Herbicide safener increases weed-management tools for control of annual grasses in wheat. Weed Technology, 1-10. doi:10.1017/wet.2020.113
Rauch, T. and J. Campbell. 2020. Herbicide Resistant Italian Ryegrass (Lolium perenne spp. multiflorum) Survey in Northern Idaho and Eastern Washington. Western Society of Weed Science Proceedings 73:48.

Extension Publications:

Lyon, D.J., J. Barroso, J.M. Campbell, D. Finkelnburg, and I.C. Burke. 2020. Best management practices for managing herbicide resistance. (PNW754).
Lyon, D.J., A.G. Hulting, J. Barroso, and J.M. Campbell. 2020. Integrated management of downy brome in winter wheat. (PNW668 revision).
Lyon, D. J., A. G. Hulting, J. Barroso, and J.M. Campbell. 2020. Integrated management of feral rye in winter wheat (PNW660 revision).
Kumar V, Liu R, Lambert T (2020) Response of Kansas feral rye populations to Aggressor herbicide and management in CoAXium wheat production system Kansas Agricultural Experiment Station Research Reports: Vol. 6: Iss. 5. https://doi.org/10.4148/2378-5977.7939