The threat posed by herbicide-resistant weeds is real.
Across Western Canada, 19 million acres are infested with herbicide-resistant weeds that are forcing growers to develop new strategies for control.
Group 1 and 2 resistance is the most common and is regularly found in wild oats across all three Prairie provinces, while in some geographies, Group 9-resistant kochia is a concern.
Both wild oats and kochia are prolific producers and their seeds can spread like wildfire. Growers must proactively take steps to delay and prevent the evolution and spread of herbicide-resistant weeds or everyone risks losing valuable control options.
An effective integrated weed management plan will incorporate diverse herbicides and crop types as well as appropriate tank mixes.
Identifying a problem
If growers notice a loss of weed control after repeatedly using the same herbicide, they may have a resistance issue.
Kara Kilden, an agronomist with the Prince Albert Co-op Whitestar AG Team, said the winter months are a great time for growers to talk with their agronomist, assess potential problem areas and develop a plan ahead of the busy growing season.
“It’s a lot of one-on-one talk with them, doing the best we can to grow the best crop we can and prevent issues for the future,” she said.
During the growing season, Kilden recommends growers scout fields routinely. When they observe problems, they should submit samples for verification.
Signs of herbicide resistance include:
- Uncontrolled weed patches scattered throughout the field don't correspond to an application pattern.
- Weather conditions are not at fault for poor herbicide performance.
- No herbicide symptoms are observed on the weed in question.
- Known cases of herbicide resistance exist in neighbouring fields.
Developing a plan
In northeastern Saskatchewan, kochia isn’t an issue for Kilden, although she is challenged by wild oats outside Prince Albert. Your local Co-op AG Team agronomist will be familiar with issues in your area.
“We haven’t seen too much of anything else right at the moment, but it’s one of those things that we watch for,” she said.
If you suspect herbicide resistance on your farm, implement control measures to guard against seed dispersal and weed spread.
An agronomist will help you understand the biology of the weeds so that you can make effective herbicide applications at the right rate and weed stage.
Best management practices to mitigate weed resistance include:
- Planting into weed-free fields and keeping fields as weed free as possible.
- Using weed-free seed.
- Using multiple herbicide modes of action in a tank mix that are effective on the same target weeds.
- Cleaning equipment when moving from a field with a known case of weed resistance.
- Managing weed seeds at harvest and post-harvest to prevent a build-up of the weed seedbank.
- Preventing an influx of weeds into the field by managing field borders.
For growers with Group 1- and 2-resistant wild oats, Kilden recommends a pre-emergent application of Avadex®, a Group 8 herbicide.
“Growers are trying to target the resistant wild oats with Avadex and then spraying in-crop with either a Group 1 or 2 herbicide. It costs more initially; however, reducing the seedbank for future years and staying ahead of the problem will set you up for success down the road,” said Kilden.
Everyone must collaborate to keep herbicide-resistant weeds at bay. By working with an agronomist and sharing information with other growers, farmers can make strategic management decisions that will keep everyone growing long into the future.
Prince Albert Co-op