Weed Menace: It’s Almost Like They Are Watching

By Gil Gullickson

The marvels of metabolism occur every time a crop plant breaks down a selective herbicide that kills adjacent weeds.

These days, though, it’s almost like the weeds are watching. That’s because biotypes of two pigweed species – waterhemp and Palmer amaranth – are mimicking the same type of metabolism field crops use to render a herbicide harmless.

Welcome to the world of metabolic resistance.

Farmers haven’t heard much about it, since target-site resistance is the source of so many of the herbicide-resistant weeds they face. Yet, metabolic resistance looms large in the weed science community. A 2018 University of Nebraska resistance survey conducted in collaboration with Kansas State University found 50% of Nebraska waterhemp plants that resisted Group 5 herbicides (atrazine) were metabolically resistant.