While cover crops provide a variety of benefits, cover crop termination in the spring requires additional management practices. Spring cover crop termination varies by cover crop species, the goals of cover cropping, whether that cover crop will be used in the spring (i.e., forage), weed pressure and species, and the proceeding cash crop.

TERMINATION METHODS

Winterkill or Winter Termination

Some cover crop species will winterkill in climates with colder winters but may overwinter in warmer climates (see table). Selecting species that winterkill can be a good starting point for new adopters of cover cropping to avoid spring termination concerns. 

Tillage

If tillage must be used for spring termination and to provide winter annual weed control, it must sufficiently disturb and uproot the cover crops to prevent regrowth; moldboard and chisel plows are highly effective. Multiple passes may be required to achieve complete termination.

Planting Green/Roller-Crimper

Planting green is planting a grain crop into a recently-terminated or living cover crop that is terminated shortly after planting. Planting green maximizes cover crop biomass production and can provide longer-term weed suppression. However, planting green can create many problems. These include: 

• Delayed planting due to cool/wet soils
• Reduced soil moisture available for the cash crop in dry years
• Problems with insect pests such as slugs and seedcorn maggots
• Interference with soil-applied herbicides

Many farmers planning to plant green significant upgrades to their planter, like a downforce system, row cleaners, and spiked closing wheels, in order to achieve satisfactory stands despite all of the biomass on the soil surface.

Roller-crimpers are often used in planting green operations and are effective methods to terminate winter rye and other cover crop species. Waiting until the boot stage of grasses or flowering prevents regrowth; however, it is important to terminate cover crops prior to seed production. Roller-crimping leaves a thick mat of biomass on the soil surface that can aid in weed suppression but can also have negative consequences, as previously mentioned. 

Herbicides

Herbicides can be highly effective for cover crop termination. When choosing herbicides, it is important to consider the cover crop species and growth stage, other weeds that may need to be controlled, the proceeding cash crop, and the weather conditions. Glyphosate, a non-selective, systemic herbicide, is commonly used to terminate both grass and broadleaf cover crops; however, the addition of 2,4-D or dicamba will improve the control of broadleaf species. Other selective herbicides could be used to manage grass or broadleaf species. Ultimately, there are a variety of herbicide options when it comes to cover crop termination; most states have recommendations for cover crop termination with herbicides. Be sure to follow all label restrictions and use any necessary tank additives or adjuvants. Also, be aware of crop rotation and plant back restrictions when choosing herbicides.

Systemic herbicides such as glyphosate, 2,4-D, and dicamba are only effective if the plant is actively growing for translocation of the herbicide throughout the plant. Air temperatures should be at least 45°F or greater when using these herbicides (some states recommend at least 50 to 55° F), and cloudy weather can limit early spring growth. Contact herbicides do not rely on translocation and are not as weather-dependent, but the chance of killing the entire plant and preventing regrowth is reduced.

Herbicides are more effective during cover crop vegetative stages. Once reproduction has started, the translocation of herbicides will be altered, and the plant may survive. Mature plant tissue absorbs less herbicide compared with young tissue. Therefore, the window for optimal control with herbicides is once the plants are actively growing and before the reproductive phases begin. 

GENERAL RECOMMENDATIONS

1. Choose a cover crop that fits your situation. Be prepared to manage overwintering species in the spring. When first starting with cover crops, start small; species that winterkill can be a good way to ease into cover cropping. Consider investing in downforce, row cleaners, and spiked closing wheels on your planter.
2. Many states offer recommendations for cover crop termination, including the use of herbicides. Other resources include the Sustainable Agriculture Research and Education (SARE) Program or the Midwest Cover Crop Council (MCCC).
3. Unless planting green, cover crops should be terminated about one to two weeks prior to cash crop planting. Many states recommend cereal rye be terminated when the plants are greater than 18 in. tall. For annual ryegrass, recommendations are often greater than 6 in. tall.