Soybean School: Waging war with herbicide-resistant waterhemp


Glyphosate-resistant waterhemp was first identified in Ontario in 2014. Since that time the weed, which hails from the pigweed family, has spread across the province with confirmed sightings in 14 counties in 2019.

To make matters more troubling, waterhemp resistance continues to grow beyond glyphosate, and now includes multiple resistance to Group 2, 5, 9 and 14 herbicides.

On this episode of the Soybean School, Dr. Peter Sikkema, weed scientist at University of Guelph’s Ridgetown campus, shares what he’s learned about the pest including: yield impact, herbicide control options and best management practices that farmers can implement to keep the weed at bay.

In soybeans, Sikkema’s research reveals that the average yield impact of waterhemp is 43 per cent, but he has documented losses of up to 93 per cent in the highest populations observed in Ontario.

When it comes to herbicide effectiveness, Sikkema reviews results from trials he has conducted and notes the most efficacious control options. In the video, he advises that if a farmer has waterhemp on their farm, they should plan to use a two-pass weed control program. “They should put down their best soil-applied herbicide and then be prepared to manage any weed escapes that may occur,” he adds. When farmers follow this program “we’re approaching near-perfect control of waterhemp in soybeans in Ontario.” (Story continues after the video).


Sikkema also emphasizes the need to follow best management practices to fend off the growing threat that waterhemp and other herbicide-resistant weeds pose across the province. These practices include diversifying rotations to include a minimum of three crops, narrowing row widths in soybeans, planting cover crops after winter wheat, and utilizing multiple herbicide modes of action.

Click here for more Soybean School episodes.


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