Editor’s Note: Crop consultants and ag retailer agronomists need to be aware of their herbicide recommendations related to cover crops for farmers who might have livestock grazing those acres.

Many farmers are now becoming more interested in cover crops due to their soil conservation and water quality benefits, and livestock producers may find them attractive as food for grazing animals. But farmers need to exercise caution when it comes to herbicide selection if they intend to graze or harvest the cover crop.

“It is important for livestock producers to consider restrictions on labels of herbicides used earlier in the growing season for corn and soybeans if they intend to use the cover crop as a forage source,” said Bob Hartzler, professor in agronomy and extension weed specialist at Iowa State University Extension and Outreach.

A new ISU Extension and Outreach publication, “Herbicide use may restrict grazing options for cover crops,” can be downloaded from the Extension Store, https://store.extension.iastate.edu. Authored by Hartzler, along with extension field agronomists Meaghan Anderson and Rebecca Vittetoe, the guide lists herbicide products compatible in cropping systems that use cover crops for forage.  

The guide contains two tables — one for corn and the other for soybeans —  that list 46 herbicides, dividing them into three categories according to the minimum interval between application and the time when cover crops can be planted. Cereal rye and wheat are cleared for planting and use as forage with more herbicides than other plants commonly used as cover crops.

Hartzler warns producers that these tables do not eliminate the need to read the label and determine specific use restrictions. The two primary reasons for these restrictions are that herbicide residues may prevent the successful establishment of the cover crop, or residue tolerances have not been established for the presence of the herbicide within the cover crop.

“Regardless of the reason for the restriction, failing to follow the label guidelines is a violation of the label and against the law,” he said.

Due to the large number of generic and private brand herbicides, the tables do not include all products, and ISU Extension and Outreach does not endorse particular brands based on their inclusion.

Despite having to pay attention to herbicide interaction with cover crops, farmers will find that they are well worth the extra effort. Cover crops reduce soil erosion, limit nitrogen leaching into groundwater, suppress weeds and increase soil organic matter.

For more information on cover crops, refer to the numerous publications and videos available in the Extension Store, https://store.extension.iastate.edu, or contact a local extension field agronomist.