Herbicide Resistant Wild Oat Herbicide Demo in Wheat-Donnelly 2021

By Calvin Yoder, Forage Seed Specialist (SARDA Ag Research/Peace Region Forage Seed Association) and Kristina Polziehn (Axiom Agronomy Ltd.)

Background

Wild oat resistance to Group 1 and Group 2 herbicides in Peace Region crops is not new, but it appears the issue is growing over the past few years. Continual use of herbicides with the same mode of action combined with poorly competitive crops, due to extremely wet weather in 2020 and drought conditions in 2021, has provided opportunities for wild oat resistance to develop. We are fortunate in the Peace Country that we are a little behind the rest of western Canada in terms of this problem, but that will change quickly if problem fields are not identified and management practices implemented.

In 2020, a SARDA Ag Research fababean research site contained an extremely high and uniform patch of wild oats there were resistant to group 1 herbicide, quizalofop-p-ethyl (commonly known as Assure II). Puma Advance (fenoxaprop-p-ethyl) a group 1 graminicide, had been sprayed on wheat the previous year. Samples of wild oat seed were collected and sent to Ag-Quest, a lab in Manitoba that specializes in testing for herbicide resistant weeds. The results showed:

• 97% resistant to fenoxaprop-ethyl (Puma Advance)

• 31 % resistant to pinoxaden (Axial)

• 5% resistant to clethodim (Centurion)

Methods

The area used to conduct pre-seed and in-crop wild oat herbicide trials had very uniform populations of wild oats from the previous year. Soil test results taken from the trial area shows a pH of 5.1, O.M of 5.1% and soil texture a clay loam. Rates of some pre-seed herbicides may vary depending on soil characteristics. It was felt that demonstrating both pre-seed and in-crop wild oat herbicides timings on wheat would be of interest to growers.

The trial area was staked out to plots 2m wide x 8 m long. Plots were replicated in a RCB design with four replications. Wheat was seeded across the trial on May 7th. Pre-seed and in-crop wild oat herbicide treatments were applied using a 2m meter handheld boom (4 nozzle TeeJet 80001) pressurized by a propane sprayer. The sprayer and walking speed is calibrated to provide 100 l/ha of water at a pressure of 270 kPa. Visual wild oat control ratings were taken several times throughout the summer. Plots were swathed in late July and material removed to reduce the spread of herbicide resistant wild oat seed.

Pre-Seed Herbicide Treatments

Most of the pre-seed herbicides have active ingredients that would not be used for in-crop control of wild oats. Wild oat pre-seed herbicides provide some residual control or suppression of early emerging wild oats reducing competition on annual crops. In most cases an in-crop wild oat herbicide is still required.

Four pre-seed herbicide treatments tank mixed with 333 ml/acre of Roundup WeatherMax were applied on May 6th one day prior to seeding wheat. Threequarters of inch of rain was received two days. Some pre-seed wild oat herbicides require moisture to move into the ground to be effective. A brief description of each product used in the trial is provided below and in Table 1. Costs are based on SRP.

Liquid Avadex (triallate): A group 15 herbicide registered prior to seeding a number of crops including wheat, barley, canola and peas. The plot area was harrowed after Liquid Avadex was applied.

Olympus (propoxycarbazone-sodium): A group 2 herbicide registered prior to seeding wheat and provides some residual suppression/control of canola, wild oats and foxtail barley.

Focus (carfentrazone+pyroxasulfone): A tank mix of Group 14 and 15 herbicides registered prior to seeding a number of on annual crops including wheat and peas. Provides some residual broadleaved and grassy weed control including activity on wild oats and foxtail barley.

Fierce EZ (flumioxazin+pyroxasulfone): A tank mix of Group 14 and 15 herbicides registered prior to seeding a number of crops including wheat and peas. Provides some residual broadleaved and grassy weed control including activity on wild oats and foxtail barley.

*Consult the label for specific information on use, weeds controlled and registered crops.

*Treatments were tank mixed with 333 ml/acre of Roundup WeatherMax ** Average of 4 reps

In-crop Herbicide Treatments

Three in-crop herbicides were applied in part of the trial area (Table 2). The herbicides were applied on June 11th when the wheat was at the 4-5 leaf stage and wild oats ranged in size from 2 to 5 leaf stage.

Puma Advance (fenoxaprop-p-ethyl): Group 1 herbicide registered on wheat and barley for wild oat control.

Sierra (flucarbazone): Group 2 herbicide registered on wheat for wild oat control.

Axial (pinoxaden): Group 1 herbicide registered on wheat and barley for wild oat control.

Results and Discussion

All pre-seed herbicides provided some suppression/ control of wild oats. Effectiveness of products on wild oats was Avadex>Focus>Fierce>Olympus. The percent control of wild oats from the products used in the trial was in line with what would be expected with each product. The degree of wild oat control with these products will vary depending on precipitation following application, soil type, crop residue in the field, application rates and water volumes.

In crop herbicide application of Everest provided good control of wild oats. Axial provided some control and Puma Advance did not provide any control. The results collected from the in-crop herbicide application were quite similar to “Herbicide Resistance Assay Results” on wild oat seed collected from the trial area in 2022.

Always remember that using different groups of preseed and in-crop herbicides for managing herbicide resistant wild oats is only one tool to managing herbicide resistant wild oats in annual crops. Adapting multiple weed management strategies can be effective in reducing wild oat populations. Greater success can be achieved when our cropping systems incorporate several integrated weed management tactics such as diverse crop rotations, higher seeding rates in cereal crops, growing competitive crops, silaging annual crops and incorporating perennial forages.