How to deal with weed resistance in IP soybeans

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Soybean quality and yield are directly linked to effective weed control, especially in conventional and Identity Preserved (IP) soybean systems. The greatest challenge lies with managing problem and hard to control weeds, and the increasing occurrence of herbicide-resistant weeds.

Approximately 22% of soybean acres across Ontario and Quebec are Non-GMO varieties.1 Unfortunately, weed resistance isn’t new for conventional and IP soybean farmers in Eastern Canada. There’s a good chance many have already been dealing with Group 2 resistance and understand that an investment in weed control will realize returns in yield and IP premiums.

To manage weed resistance in IP soybeans, farmers need to establish a clean field before emergence and employ multiple effective modes of action.

Start clean

The best strategy for reducing yield losses in any type of soybean system is to start with a clean field at planting, either through tillage or an herbicide application. After that, the availability of post-emergence weed control options in IP soybeans becomes very limited. That’s why IP farmers should do everything they can to eliminate annual weeds before crop emergence so that any escapes don’t become a trial to clean up.

A pre-emergence herbicide pass is an effective practice, but as with timing any application, working with the weather can be challenging, especially early in the growing season. Read and follow herbicide label directions carefully, understanding product performance requirements like rain activation. Remember, the critical weed-free period in soybeans is V1 to V3, and the presence of weeds during this time directly impacts yield potential.

Striving for perfection with the first pass over the field is an investment in soybeans and will pay off with fewer headaches as a result of managing weed escapes, higher yields and improved quality and crop premiums.

Fight weeds with multiple effective modes-of-action

Herbicides contain one or more active substances known as modes-of-action that make up the molecular basis for how these actives kill or damage weeds. Using different methods of controlling and eliminating target weeds (modes-of-action) reduces the likelihood the weed will be able to overcome multiple methods of control and reduce the risk of it rapidly developing resistance.

Incorporating at least two effective modes-of-action into an herbicide application will diversify the approach to controlling target weeds. This method also reduces the risk of resistance, increases overall weed control and reduces seed return to the soil.

Chemistry Groups 5, 14 and 15 have proven to be useful resistance fighters in soybean weed control programs. The easiest way to incorporate multiple modes-of-action is to select a herbicide like Commenza™ that offers three effective modes-of-action on Eastern black nightshade – Groups 2, 5 and 15 – significantly increasing the chances of successful weed control.

Adding chemistry groups to a tank mix is another option to incorporate multiple effective actives. Be sure to read and follow product labels and consult a trusted advisor for advice on selecting and mixing herbicides.

No matter the soybean management system, farmers should be on the lookout for the development of resistant weeds. Common ragweed resistance to Group 14 was identified in Ontario in 2023, marking the rising rate of development.

Curious about resistant weeds in your area? This herbicide resistant weeds - database and maps features herbicide resistant weed species in Ontario that have been confirmed through testing.

For more information about managing weeds, especially hard-to-control and resistant weeds in conventional or IP soybean systems, talk to your local retailer, agronomist or Corteva Agriscience Retail Territory Manager.

1Stratus Market Research 2023