When growers talk about the benefits of cover crops, the talk normally centers around erosion control, keeping nutrients in the field, improving soil quality and trimming fertilizer purchases. 

More effective weed control is another benefit. In fact, some no-tillers have found cover crops enable the avoidance of at least one costly herbicide trip across their fields per year.

Adam Davis has research that indicates cover crops offer significant benefits in suppressing weeds. “Cover crops are one of the ways to do it, so your herbicides have to do less work and we’re not placing all the of the weed control burden on them,” says the University of Illinois weed scientist. He cites several ways no-tillers are using cover crops for suppressing weeds.

Less Weed Establishment

Davis says cover crops help prevent weed establishment and germination. Even the few weed seeds that germinate often die or are stunted due to low light conditions and allelopathy concentrations often found with an early mat of cover crop growth.

Reduced Weed Seed Banks

Davis says cover crops reduce weed seed production, keep weed seeds away from the surface, increase weed seed decay and increase weed seed consumption by beetles, crickets and mice.

He’s found adding a legume to a cover crop and no-till program offers a more favorable habitat and can double the rate of weed seed consumption by these predators. Anywhere from 40-90% of new weed seeds can be consumed during the growing season.

Weed Interference

Davis says the allelopathy effect often found with cover crops offers still another defense against weeds, as they can release their own weed control chemicals into the soil. Since cover crops are nutrient scavengers, they also take up nitrogen that would otherwise be used by winter annual weeds.

Davis says the phytotoxins produced by cover crops interact with herbicides. They aid in weed control and may reduce resistance to herbicides. In fact, researchers are evaluating how cover crops could tie up the resistance susceptibility traits in some weeds.

Davis says the return on investment for herbicides has been decreasing steadily over the past 3 decades. With resistance increasing with all major herbicide modes of action, cover crops may prove to be a way to help reduce weed resistant concerns.