Cover crops are an effective tool for fighting herbicide-resistant weeds, says Daniel H. Smith, nutrient and pest management program manager for the Univ. of Wisconsin-Madison. They add a layer of complexity, but Smith says they’re a key part of a systems-based approach to weed control.

“Our first purpose within the system is to find a goal for the cover crop,” Smith says. “If we’re going after weed suppression and erosion control, small grains do quite well. They help crush herbicide-resistant weeds with a nice biomass and mulch layer.”

Smith says winter cereal rye lends well to this goal due to its ability to overwinter and produce a large amount of biomass. It begins growing at 40 degrees F, giving it about 10 extra degrees of growth compared to corn. That equates to about a month of extra growth in most settings, according to Smith.

“Think about maximizing early spring biomass,” Smith says. “Planting dates are inherently important for yield, and you’re going to want to find that middle point of maximizing yield and weed control for the best results possible.”

Based on research from Rodrigo Werle, weed scientist at UW-Madison, Smith recommends aiming for 4,600 pounds of cereal rye biomass per acre on the field. Rye will typically be knee to waist high to produce this amount of biomass. He says 4,600 pounds will be hard to achieve with corn, but it works with soybeans.

“Spring termination is really important when we’re thinking about the system,” Smith says. “We could plant soybeans into the rye, let it grow a little longer and terminate it later. Maximizing the amount of biomass reduces the waterhemp population by 50% and controls most weeds in soybeans.”

Smith says termination timing is critical in a system that includes cover crops. Nighttime temperatures above 50 degrees F and daytime temperatures above 60 degrees F for 3 days before and after application are necessary for glyphosate to translocate, according to Smith.

While some farmers are concerned about covers impeding the pre-emergence herbicide pass, Smith says his research shows that the herbicide will still make it through the cover crop residue to the soil surface.

For more insight from Daniel H. Smith on how to manage weeds in your strip-till operation, read Michaela Paukner’s article “How to Control the 3 Most Challenging Weeds in Strip-Till” featured in the Summer 2026 issue of Strip-Till Farmer.