Glyphosate resistant waterhemp has spread from Essex Country, Ontario, all the way to Leeds-Grenville County, nearly 700 kilometres away in just seven growing seasons.

While the exact path of spread is not known, Dr. Peter Sikkema, weed management professor with the University of Guelph, says that introduction can be through wind dispersal, in livestock feed, or seed.

No matter how it travels, trying to tame this resistant weed requires planning, and as Sikkema explains in Day 1 of the 2021 Ontario Diagnostic Days, a two-pass plan is likely the standard now.

Sikkema says that there is already confirmed resistance to herbicide Groups 2, 5, 9, and 14 in Ontario. Upon further testing, it has been found that the waterhemp genetics first found here that were resistant to glyphosate likely originated in Missouri.

Because of the multi-active resistance, Sikkema has been evaluating several two-pass herbicide strategies using two or more products. His work suggests that an effective soil-applied product plus an in-crop option should be the base of any waterhemp control strategy.

“The key there, is even in a dry year the soil-applied product will offer some control. It’s up to farmers and agronomists to then scout and control the “escapes” or later emerging population of the weed. Planning for a pre- and post-emerge system is required because when you’re drawing up plans in March, you don’t know what the moisture conditions will be like at planting, or how dense the waterhemp will be,” he says.

In Sikkema’s work, his team has looked at several soybean types, and have used Zidua plus Sencor, and Zidu, plus Sencor, plus Liberty in-crop for effective options. The approach is similar in corn, he says.

A three-product system can achieve nearly 100 per cent control, he says.

“Every farm should start with your best set up program, and plan for a post-emerge pass if there are escapes,” he says. Without management of those escapes, you can approach 100 per cent yield loss over time.

Watch or listen to the entire discussion on herbicide options with Dr. Peter Sikkema, here!

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