Utilizing Multi-Mode-of-Action Herbicides to Combat Resistance in Canadian Pulse Fields

The success of pulse crops in Canada can be diminished by weed resistance issues that have developed from the repeated use of certain herbicides. However, one of the best tools to manage resistant weeds and slow the development of resistance is to use herbicides with more than one effective mode of action (MOA). Not only can this help to control resistant weeds today, but it can also help protect the prosperity of future pulse crops.

Resistance issues in detail 

While pulses are a valuable crop for western Canadian farmers, they aren’t very competitive. Weeds can easily outcompete crops especially when growers rely solely on in-crop herbicides, Plus, there aren’t many in-crop herbicide options when it comes to pulses.  Kochia, green foxtail and wild mustard are all weeds that are often considered to be particularly competitive, and many are resistant to common herbicides.

Herbicide resistance won’t go away, so growers need to be mindful of their herbicide rotations in an effort to slow the spread of resistant biotypes. 

Protection with multi-MOA 

Herbicides with two or more effective MOAs are great tools to slow resistance development to a single active ingredient or mode of action. An effective way to apply multiple modes of action from a herbicide in Canada is in tank-mixes, where two or more products are combined and used at the same time. Sequential programs, where different herbicides with different modes of action are applied at different stages of a crop or weed’s growth is another way to prolong the longevity of effective herbicides. The use of pre-emergent soil active herbicides has been widely adopted by pulse growers in Western Canada. These products often feature effective active ingredients from modes of action which are not used at in-crop herbicide timing. Many of these products provide up to 8 weeks of broadleaf and/or grass weed control after receiving activating moisture, either through snowmelt or rainfall in the spring. These products not only add a new mode of action to the herbicide plan, but they also introduce a new herbicide application timing. Weeds can adapt their growth pattern based on routine, so adding a new timing that also includes multiple weeks of control early in the season throws weeds off and helps farmers get their pulses off to a competitive start.

Early weed control also helps make in-crop herbicide applications more effective. Later flushing weeds will be smaller and smaller weeds are generally more susceptible to herbicides.

Advantages of using two modes of action in field peas

Multi-mode-of-action herbicides can offer pulse growers several advantages, including:

• Improved weed control: With less chance of resistance development
• Improved yields: With less competition from weeds and with herbicide for field peas applied early to give effective results, performance and yield can be maximized
• Future sustainability: Rotating and combining MOAs where possible helps growers slow the development of resistance, and helps preserve the longevity of certain herbicides.
• Improved season-long opportunity: Dealing with weeds early in the season can potentially offer growers the gift of time and flexibility later in the season by reducing weed pressure and allowing the crop to get off to a more competitive start.

Resistance integrated into crop planning 

Field scouting and note taking, while a simple practice is important in identifying and managing weed-resistance. Understanding trends and anomalies in, what was applied, when it applied and what was were the results can help growers identify resistance probabilities earlier and adjust their integrated weed management systems accordingly.  

The best approach to dealing with herbicide resistance is one that is proactive, not reactive. Waiting until a resistance issue is clear and a serious problem will leave pea growers with fewer options and, more likely, increased costs. Using multi-mode-of-action herbicides as part of a crop protection plan means that growers will have the best chance of keeping their fields protected and productive year after year.

Resistance issues have been in Canada for many years, and they’ll only continue to spread. That is why it is so important for growers to do what they can to slow down the spread of resistance to help maintain the efficacy of our herbicide options and allow field peas to continue being a beneficial and economic crop in the future.