Termination

Terminating with translocated herbicides is much more effective with warm temperatures and when the cover crop is actively growing. Nonselective, contact herbicides can also be effective depending on cover crop size and growth stage.

For optimal control, some cover crop species may require a second herbicide application two to three weeks after the initial one. You can combine this second application with residual herbicides to improve weed control in the succeeding crop.

If you use an herbicide to terminate a cover crop, always consult the product label and your state or provincial weed control guide first. These local guides provide the most current legal and effective herbicides for your location and cropping system.

Access to your own spray equipment or good communication of the herbicide plan with the applicator is important to ensure good timing of application with consideration of environmental conditions.

Consult your state or provincial resources for more details on the effective use of herbicides in early spring.

Things to consider when applying herbicides:

• Spray water quality and conditioning, adjuvants, and tank mixes. See: Impact of water quality on pesticide performance
• Nozzles and spray volume. See: Sprayer Nozzle Know-How
• Air temperature. See: How Temperature and Rain Can Affect Burndown Herbicides and Temperature and Herbicide Application Questions
• Time of Day.

Glyphosate specific information on the considerations listed above available here: Understanding Glyphosate to Increase Performance - Purdue Extension

If you use herbicides to terminate a cover crop, always consult the product label and your state or provincial weed control guide first. These local guides provide the most current legal and effective herbicides for your location and cropping system.

Find weed control guides for your state or province here.

Frost or extended periods of freezing will usually terminate warm-season and certain cool season cover crops such as buckwheat, oat, and radish. However, chemical or mechanical methods may be required to terminate winter hardy cover crops such as rye, ryegrass, and hairy vetch.

Using tillage to terminate cover crops can be accomplished in conjunction with other mechanical or chemical methods or as a standalone method. A moldboard plow, heavy disk or specialized combination tools may be used depending on the biomass accumulation and desired cover crop surface residue needed to meet the growers’ objectives. The termination and incorporation of green biomass that usually consists of higher tonnage and higher protein (Nitrogen) composition is often referred to as “green manuring”.  Since this green biomass is a quality food source for soil biota, it can provide more rapid carbon and nutrient cycling which speeds the release of plant available nutrients and a temporary increase in important soil functions. These short-term gains can be at the expense of soil surface armor, habitat for beneficial organisms, and long-term improvements in soil structure and soil functions especially if tillage becomes annual standard operating procedure for termination. When tillage termination is planned, it is generally advantageous for soil health to allow significant biomass accumulation. Be aware that concentrations of incorporated cover crop biomass in and around the cash crop seeding depth zone can be detrimental to germinating seeds when the cover crop biomass contains allelochemicals, host traits for pathogens, or create an uneven seed bed.

Mechanical methods are also effective ways to terminate cover crops. Mowing, can successfully control some cover crops at the flowering or heading stage. Using a moldboard plow or heavy disc can control cover crops very effectively and increase the rate of N availability from legume cover crops, although it leaves the soil surface vulnerable to erosion and oxidizes soil organic matter.

Grazing alone is generally insufficient to terminate cover crops and is not an acceptable termination method for crop insurance purposes. Consult your local extension service or conservation agency for grazing considerations with cover crops. Be sure to follow herbicide restrictions for cover crops intended to be grazed.

Using a roller crimper can successfully control some cover crops at the flowering or heading stage. For optimal control with a roller crimper, you need to crush the stems of cover crops rather than bend them. Be aware that roller crimping is an advanced termination strategy that requires careful management. For more information on roller crimping, you can visit the following:

• Introduction to Cover Crop Rolling - Virginia Resource Conservation & Development Councils
• University of Wisconsin - Integrated Pest Management Videos
• A Roller-Crimping for Cover Crop Termination and Weed Suppression - University of Nebraska