Cover crop termination challenges with a cool spring

April 9, 2018 3:04 PM
Blog Post

Green cover crop fields are slowly starting to appear across the state. Despite the recent snow that fell across the state, #plant18 is right around the corner. Farmers should have a game plan in place for how they plan to terminate their overwintering cover crop. Killing cover crops with a herbicide is the most common termination method. However, the effectiveness of herbicides at terminating a cover crop depends primarily on three things: 

  1. the cover crop species and growth stage;
  2. the herbicide and rate used;
  3.  the environment.

The cool temperatures we’ve been experiencing may make terminating cover crops this spring more challenging. 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 lb acid equivalent rate of glyphosate. This could be anywhere from 28 fl oz to 42 fl oz, depending on your formulation of choice. Glyphosate formulations many contain from 3 to 4.5 lb 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 of choice to determine the appropriate application rate. Since glyphosate is a translocated herbicide, the most effective herbicide applications will be made on a sunny day when temperatures are above 60°F, plants are actively growing, and nighttime temperatures stay above 40°F.


The cereal rye cover crop at the ISU McNay Farm planted early September 2017 slowly starting to green-up this spring. Photo taken March 30, 2018. 

Cool spring temperatures mean cover crop plants aren’t actively growing. Vegetative growth in rye requires temperatures of at least 38 F. While air temperatures may be good later this week, soil temperatures are cooler and may slow growth.  Consequently, the plants may have trouble taking-up herbicides and termination may be compromised. Leaving a small check strip is a simple and easy way to see if the cover crop is dying following termination.

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

Waiting to terminate until after your crop is planted, especially in non-GMO crops, can be very 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 www.cdms.net or www.greenbook.net.

Additional information on cover crop termination:

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Rebecca Vittetoe Field Agronomist in SC Iowa

Rebecca Vittetoe is an extension field agronomist in southeast/south central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, so...