Weed Wisdom Feb. 2020

Glyphosate-resistant wild oat in Australia

By Dr. Charles Geddes

A recent discovery uploaded to the International Survey of Herbicide-Resistant Weeds (weedscience.org) confirmed one of our biggest fears with respect to herbicide resistance on the Canadian prairies. Glyphosate-resistant wild oat was confirmed in a chickpea field near Queensland, Australia. Interestingly, the researchers confirmed glyphosate resistance in both wild oat (Avena fatua) and sterile oat (Avena sterilis) species collected from the same field.

wild oat plant
A wild oat plant well on its way to seeding.

Wild oat is at the top of the list of weed species with the greatest potential to be selected for glyphosate resistance in western Canada, followed closely by false cleavers (commonly referred to as cleavers).

Of course, glyphosate-resistant wild oat would be highly problematic for prairie farmers, who are already battling with wild oat resistant to group 1, 2 and 8 herbicides. While a recent confirmation in Manitoba also showed five-way resistance in one wild oat population to herbicides within the groups 1, 2, 8, 14, and 15.

The prairie herbicide-resistant weed surveys suggest that herbicide-resistant wild oat is currently present in more than half of the fields where wild oat seed is collected and tested. While group 1-resistant biotypes are the most abundant, this type of resistance has caused many growers to shift to the use of group 2 herbicide for wild oat management, resulting in an increase in group 2 resistance as well. Wild oat populations with multiple resistance to herbicides within groups 1 and 2 are present in over one quarter of the fields tested in the prairie surveys.

Growers dealing with group 1+2-resistant wild oat (assuming blanket resistance to all of the active ingredients within these modes of action) are limited to pre-emergence herbicide options only. With the exception of a select few, many these herbicides are rated for suppression rather than control (consult the Guide to Crop Protection or the herbicide label). This makes the potential loss of efficacy of glyphosate for wild oat control a much higher threat to our cropping systems.

wild oat seedling
Wild oat showing up in spring.

Ongoing surveillance efforts in Canada suggest that the glyphosate-resistant wild oat biotype is not present on the Canadian prairies yet. We encourage growers who experience lack of wild oat control using glyphosate to take advantage of diagnostic testing. The AAFC Prairie Herbicide Resistance Research Lab offers free confidential testing for glyphosate resistance in all weed species (with the recent exception of kochia). For more information, pleased contact Dr. Charles Geddes (Charles.Geddes at canada.ca) or submit a sample using this sample submission form.