Corn and Soybean Herbicide Options for Planting Cover Crops for Forage in Fall

By Amit Jhala, Extension Weed Management Specialist, Bruce Anderson, Extension Forage Specialist, and Mary Drewnoski, Beef Systems Specialist

When growers add cover crops, it's important to select and manage the crop according to the primary objective for the crop. Cover crops usually are planted to benefit the soil and are not harvested. Some cover crops may be suitable for grazing or haying though, which means they MUST be selected and managed as forage crops when making herbicide choices.

As growers plan to buy seed and herbicides, it is important to know which herbicides should be applied in corn and soybean if they are planning to plant cover crops and use them as forage (also known as "forage double crop"). Most corn and soybean herbicide labels categorize several cover crop species as "other rotational crops," meaning that plant-back restrictions will usually be 18 months or more.

Cover crops that are NOT harvested can be planted after any herbicide application in summer crops, but growers assume the risk of crop failure, if the cover crop species is not listed on the herbicide label. However, for growers who use their cover crops as forage or feed, this off-label herbicide activity constitutes breaking the law. An EPA registered herbicide label is a legal document and the instructions must be followed to avoid violating federal law.

It can be difficult to find information on which herbicide(s) to use or avoid for certain cover crops, especially when planning to use the cover crop for forage or feed (forage double crop). Due to the crop rotation interval specified on the label, the herbicides listed below can be applied in corn or soybean and forage double crops can be planted in the fall after corn or soybean harvest. Note that only the listed forage double crop can be planted and used for forage. When tank-mixing with other herbicide(s), refer to all relevant labels for rotational/re-cropping instructions, following the most restrictive intervals.

SOYBEAN HERBICIDES

Soybean Preemergence Herbicides:
AUTHORITY ASSIST: Cereal rye and wheat can be planted 4 months after Authority Assist is applied preemergence in soybean. This interval is 18 months for Minnesota and North Dakota, north of Highway 210. Do NOT feed treated soybean forage or hay to livestock.

DUAL II MAGNUM: If not more than 1.33 pint/acre of Dual II Magnum is applied to the soybean field, carrot, radish, and turnip can be planted 60 days after the last application. Alfalfa can be planted 4 months after application. A second application of Dual II Magnum or other herbicides containing Dual II Magnum (S-metolachlor) is prohibited when planting the above-mentioned forage double crop in fall.

SHARPEN: Sharpen can be applied preemergence in soybean at 1 fl oz/acre if the organic matter content of the soil is more than 2%. This herbicide will provide limited broadleaf weed control at this rate. Coarse soils with less than 2% organic matter require a minimum preplant interval of 30 days for planting soybean. Several forage double crops, including barley, cereal rye, oats, pearl millet, sorghum, and triticale can be planted after soybean harvest without restriction. Field peas and chickpea can be planted 60 days after applying Sharpen.