Metabolic Weed Resistance Crisis Builds Across The Heartland

The problem is making it difficult for farmers to know which herbicide chemistries will still work in their fields.

Waterhemp, Palmer amaranth and some other tough broadleaf weeds and grasses are no longer slipping past just single herbicides. Across the Corn Belt and beyond, they are tolerating entire herbicide programs. Weed scientists say that pattern points to a critical issue more farmers are facing: metabolic resistance.

Unlike traditional target-site resistance, which is often specific to a single herbicide class, metabolic resistance is even worse because it can confer cross-resistance to multiple, unrelated herbicide groups.

Aaron Hager, University of Illinois Extension weed scientist often warns that when a tough weed like waterhemp learns to metabolize one herbicide, it becomes easier for it to “learn” to detoxify others. That ability has helped lead to the 7-way resistance with waterhemp seen in some Illinois counties, according to weed scientist Patrick Tranel, one of Hager’s colleagues.