Waterhemp is a dioecious (male and female flowers on separate plants) pigweed with a high genetic diversity. Consequently, this pigweed has a high propensity to adapt to control tactics and has evolved resistance to herbicides from as many as 6 or 7 different herbicide groups (HGs). Out of 75 waterhemp populations collected from corn/soybean fields in Iowa in fall 2019, almost 25% had a four-way multiple resistance to HGs 2 (ALS inhibitors), 5 (atrazine), 9 (glyphosate), and 14 (PPO inhibitors). It is important to use a diverse herbicide program with multiple, effective sites of action to reduce overreliance on any single herbicide and slow further development of herbicide resistance in waterhemp.
Iowa State University
Jha, Prashant, "Herbicide Programs for Waterhemp Control in Soybean" (2021). Integrated Crop Management News. 2690.
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