This year’s late-developing spring has posed challenges to farmers trying to find a window to terminate overwintering cover crops such as rye. Even if you had a game plan in place, the snow and cold in April likely postponed and changed those plans.

Killing cover crops with herbicide is the most common termination method. Keep in mind, however, the effectiveness of herbicides at terminating a cover crop depends primarily on three things: cover crop species and growth stage, herbicide and rate used, and the environment.

Using glyphosate alone is the safest bet to getting the cover crop killed in a timely and effective manner. It is recommended to use a 1-pound acid equivalent rate of glyphosate per acre. This could be anywhere from 28 to 42 fluid ounces, depending on your formulation of choice.

Glyphosate formulations may contain from 3- to 4.5-pound acid equivalent per gallon; the concentration of a formulation is listed below the ingredient statement on the first page of the label. Be sure to check your product to determine the appropriate application rate.

Soil temperature key
Since glyphosate is a translocated herbicide, the most effective herbicide applications will be made on a sunny day when temperatures are above 60 degrees F, plants are actively growing, and nighttime temperatures stay above 40 degrees.

This year’s cool spring temperatures resulted in slow growth with overwintering cover crops. Vegetative growth in rye requires temperatures of at least 38 degrees. While air temperatures may have been warmer, soil temperatures were cooler, which slowed growth. Timing a termination when growth is slowed may have resulted in the cover crop dying slower or termination being compromised. Leaving a small check strip is a simple and easy way to see if a cover crop is dying following termination.

Iowa State University researchers generally recommend terminating a cover crop with herbicide 10 to 14 days prior to planting corn to protect yield. However, that time frame is less critical for soybeans. Always check with your crop insurance agent for any specific cover crop requirements they may have prior to planting corn or soybeans.

Terminating cover crop
Waiting to terminate a cover crop until after your corn or soybean crop is planted, especially in non-GMO crops, can be risky. Options become more limited, and the cover crop can quickly become an uncontrollable weed.

Always look at the herbicide labels for directions and any restrictions for the subsequent crop. A quick and easy place to look up herbicide labels is cdms.net or greenbook.net.

Additional information on cover crop termination:

• ICM Blog: Terminating Cover Crops: What’s your Plan?

• ICM Article: Terminating Cover Crops

• ICM Article: Research Shows Extra Cover Crop Growth Prior to Soybeans Provides Benefits

• ICM Article: Cereal Rye Cover Crops, Allelopathy and Corn

• Cover Crop Termination, IPM University of Illinois

• Cover Crop Termination, University of Wisconsin Extension

• Successful Cover Crop Termination with Herbicides, Purdue Extension

Vittetoe is an Iowa State University Extension field agronomist in south-central Iowa. Contact her at [email protected].