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Ontario Grain Farmer Magazine

New Ontario solutions for wild oats control in spring wheat and barley

Principal Investigator: François Tardif

Research Institution: University of Guelph (U of G)

Timeline: April 2020 – March 2022

Objectives:

  • Identify herbicides which will provide excellent control of wild oats with a high level of crop safety.
  • Contribute data to allow for registration of new wild oat products.

Impacts:

  • Proactive action on wild oats will reduce losses in yield and quality due to the presence of uncontrolled populations of that weed.
  • Create a list of BMPs that will allow producers to adjust their practices and minimise production risks caused by resistance.

Scientific Summary:

Wild oat is an important global weed that is especially troublesome in areas where spring cereals (wheat, barley, oats) are extensively grown. The similarity in form and growth habit between wild oats and small grains make it especially competitive and hard to control. Since the late 1970s, control of wild oats in wheat and barley has relied mostly on the development of effective selective post emergence herbicides belonging to groups 1 and 2. Unfortunately, the efficacy of these herbicides has resulted in the development of herbicide resistant (HR) wild oats in many areas such as Australia and western Canada. In Ontario, herbicide resistant wild oats have not appeared to develop to the same extent, probably due to the lesser importance of spring cereals in our cropping systems; however, there have been multiple reports in the last few years of increasing incidence of HR wild oats in Ontario which make control very challenging.

As reports of resistance to group 1 increase in Ontario, there is a need to explore new herbicide options that are cost-effective under our conditions. Candidate herbicides would be products that are currently registered in Western Canada but not in the East because of our smaller market share. Other potential herbicides would be products that have some grass control efficacy in other crops (e.g., corn). The ultimate goal was to identify products that could provide enough control of wild oats while providing adequate crop safety. Field trials were conducted at two farm locations with a wild oats problem. Small plots were planted with spring wheat and spring barley and sprayed with the selected herbicides at the required timings (PRE or POST). Data recorded included wild oats control efficacy and biomass, crop injury, crop biomass and crop yield.

Results

Field trials were conducted at the Elora and Woodstock research stations in 2020, and on-farm and at the research stations in 2021. Following discussion with GFO, further on farm testing was done in 2022. For the on-farm trials, we were able to coordinate with two cooperators, one at Flesherton (2021), the other at Orangeville (2021-2022). According to the cooperators, each of these sites had significant herbicide resistant wild oats infestations. The Flesherton site was planted to wheat and the Orangeville site was in barley. The on-station trials were a repeat of the 2020 trials: tame oats were seeded in spring wheat and spring barley plots to serve as a surrogate for wild oats.

Treatments in 2020 were as follows:

1.       Avadex Liquid (PPI)

2.       Avadex Liquid (PPI) fb Puma Advance (POST)

3.       Avadex Liquid (PPI) fb Achieve SC (POST) + Turbocharge

4.       Avadex Liquid (PPI) fb Axial

5.       Avadex Liquid (PPI) fb Varro + Agral 90

6.       Focus (PRE)

7.       Fierce WG (PRE)

8.       Puma Advance (POST)

9.       Achieve SC (POST) + Turbocharge

10.     Axial (POST)

11.     Varro (POST) + Agral 90

12.     Simplicity GoDRI (POST) + Agral 90

13.     Untreated check

Compared to 2020, three additional treatments were added in 2021 and 2022: a) Sencor, which is registered in Western Canada for control of many species in spring wheat and spring barley; b) the addition of AMS as an adjuvant to Varro as the label mentions it can be added to enhance activity; c) Osprey, which is a group 2 herbicide registered in the US for wild oat control.

Varro, Simplicity and Osprey (group 2 herbicides) provided high levels of wild oats (or tame oats) control. Wild oats population that are only resistant to group 1 herbicides could therefore be effectively controlled by these products. However, there are a few important considerations:

1) If the wild oats were to also have group 2 resistance, then the efficacy of these three products might be reduced;

2) The level of injury to barley with Varro and Simplicity was very high, contributing to yield losses;

3) Osprey was one of the most effective herbicides as it provided high oat control and caused low wheat injury, resulting in high wheat yields. In barley, injury was low and yields not affected. However, this herbicide is not registered in Canada in either crop and whether the manufacturer would support such registration remains to be determined.

Focus (groups 14+15) and Fierce (groups 14+15) applied PRE did not provide consistent control of oats in either wheat or barley. However, they were generally safe to both crops and did not reduce yields. Therefore, regardless of their limitations, they might be an option especially when dealing with multiple resistant wild oats.

Sencor (group 5) provided variable control of oats and the wide range of efficacy would make it a less desirable solution. In addition, injury to wheat, and to some extent barley, was relatively high, which had negative impacts on yields.

Avadex is applied PRE and it needs to be incorporated in the soil immediately following application. When applied alone, it provides variable control of oats ranging from <5% to 95%. Injury to wheat and barley was low and yields were not statistically different from those in the untreated plots. Efficacy on oats was dependent on the sites; at the two farm locations where wild oats populations were low, Avadex provided high control; however, at the two research stations, control of tame oats was lower, probably due to higher densities.

Alternatives to group 1 herbicides exist, but there are limitations to each of them. In wheat, group 2 herbicides are the most effective and safe and they are an alternative to group 1 products when there is resistance to these. In cases where there would also be resistance to group 2 herbicides, the efficacy of some or all of these group 2 products might be reduced. Other modes of action are either too injurious to the crop or too variable in the level of control they provide. In barley, there seem to be less options at this stage with the group 2 products causing too much injury. The search for alternatives will continue although future solutions may not be entirely herbicide based and would require integration of other methods.

Recommendations to producers:

1. If resistant wild oats are suspected, then the first thing to do is to collect seed so that herbicide resistance testing can be done.

2. Testing should be requested for the following herbicides (Note: Each of these herbicides represents a different sub-group within groups 1 and 2 and we have found in the past that resistance is not always uniform within a group):        

          Group 1 herbicides

          -Puma (fenoxaprop-ethyl)

          -Achieve (tralkoxydim)

          -Axial (pinoxaden)

          Group 2 herbicides

          -Varro (thiencarbazone)

          -Simplicity (pyroxsulam)

3. Do not assume that one wild oats sample from one field represents the whole population. Distinct patches should be sampled and tested separately as these may have different resistance patterns. For example, one patch may have only resistance to Puma while wild oats in another patch could be resistant to all group 1 and 2 herbicides; such a result would influence the management decisions.

4. For example, if resistance is confirmed to only Puma, then one would be able to use other group 1 herbicides, like Axial or, preferably, a group 2 product.

5. If the resistance is affecting all group 1 and group 2 herbicides, then the options are much more limited. One recommendation in spring wheat is to use Fierce or Focus as a PP or PRE applications, which are registered treatments. This may provide acceptable control, but one would need to accept the fact these treatments may provide very variable results. In our trials, efficacy ranged all the way from 0% to 95%.

6. Research on other methods of control such as micro inter-row cultivation, precision herbicide application with shrouded sprayers and harvest weed seed control is currently underway in Western Canada. Whether these methods are acceptable and would be applicable to Ontario conditions remains to be seen.

7. There is a need to keep the conservation going with herbicide manufacturers so that new herbicide modes of action are available for wild oats control.

External Funding Partners:

Valent

Corteva

FMC

Gowan

Project Related Publications:

None.