Will Herbicide Carryover Hurt Fall-Seeded Cover Crops?

Corn and soybean herbicide carryover can impact fall cover crop stand establishment.

Published on: Aug 22, 2012

The question about whether corn or soybean herbicide programs will pose a problem for seeding fall cover crops arises again, particularly in areas of severe drought where corn is harvested earlier than normal and the desire to plant a cover/forage crop is strong. So here's a best-guess assessment from Bill Curran and Dwight Lingenfelter, Penn State Extension weed specialists.

If you look at the rotation crop restrictions for corn and soybean herbicides in the Agronomy Guide (Tables 2.2-17 and 2.4-15), you'll see that many products limit rotation to alfalfa and/or clover as well as some of the small grains. This is a good place to start when thinking about rotation to fall cover crops.

Will Herbicide Carryover Hurt Fall-Seeded Cover Crops?
Will Herbicide Carryover Hurt Fall-Seeded Cover Crops?

However, these tables are inadequate. Cash crop rotation restrictions center concern for herbicide residues accumulating in forage or feed, not carryover injury. If the crop is not going to be harvested and consumed by livestock or humans, then the primary concern is carryover injury and achieving an acceptable stand that provides the benefits of a fall or winter cover.

While few cover crops are listed in these Agronomy Guide tables or on herbicide labels, look for close plant relatives to get an idea of how certain species may succeed. For example, there's no listing for the legume hairy vetch or the mustard daikon radish. But by looking at the alfalfa or clover restrictions or at annual mustards such as canola you can "guesstimate" which herbicides may cause potential injury to related cover crop species.

Where the greatest concern is
In general, products with a four month or less rotation restriction for the species of interest, close relative, or sensitive species (i.e. clovers) should pose little problem.