How to Reduce Herbicide Carryover Risk in Your Fields

Most herbicides are formulated with some form of residual activity, extending the life of their weed control. But when herbicides persist in the soil too long, they can cause problems for the following year’s crop.

“We want residual control, in some of our herbicides, to control our weeds for three to five weeks,” said Wesley Everman, an Iowa State University Extension weed specialist. “We usually don’t want [control] to last beyond a couple [of] months. It really becomes an issue if it persists for 10 or more months because then, we’re impacting next year’s crop, and its growth, and potentially its yield.”

How Herbicides Break Down
Many herbicides are broken down by microbial degradation. In short, the carbon bonds and molecules within a herbicide formula serve as a food source for soil microbes. “The faster the microbes do their work, the less herbicide activity we have over time,” Everman said.