Cover Crop Termination

Introduction

• Cover crops can increase soil organic matter, decrease soil erosion, and—depending on the species—supply nitrogen and suppress weed densities for the next cash crop.
• Timely removal of a cover crop can help maximize benefits and minimize any negative impact on the yield potential of the following crop.
• Removal timing and removal method is specific to the cover crop species planted.

Timing of Cover Crop Termination

Generally, cover crops—especially cereals—should be terminated two to three weeks before seeding commodity crops.¹ However, the removal timing is specific to each cover crop species, the farmer’s goals, the particular growing conditions, and the following cash crop. For example, terminating cereal rye at least two weeks prior to commercial corn planting can help avoid negative early growth effects from cover crop biomass.² But terminating cover crops such as radish and oats immediately before commercial corn planting may be an option when starter fertilizer is used to lessen the risks of nutrient deficiency. Early termination of small-grain cover crops can result in more rapid decomposition of the residue due to the low carbon-nitrogen ratio of young plant tissue. Conversely, higher carbon-nitrogen ratios are reached at the flowering stage of small grains, which may be desirable for increasing aboveground biomass production and soil coverage.¹

For research on cover crop termination timing and tillage, visit Effect of Tillage Practice on Cover Crop Termination Timing on Soybean Production. For cotton producers specifically, cover crops termination timing can affect the ‘green bridge’ for insect survival. Read more on research surrounding cover crop use in cotton here: Cover Crop Termination in Cotton.

Cover Crop Termination Methods

Winterkill Termination Method

The winterkill termination method leaves cover crops in fields until they are terminated by a hard freeze. This method is possible in northern climates and for certain cover crops such as oats and oil seed radish (both winterkilled at 20 °F) or brassicas (winterkilled at 15 °F).³ Frost susceptibility can vary with a species’ winterhardiness, winter temperatures, and snow cover.⁴ Some winter annual cover crops, such as crimson clover and annual ryegrass, could be winterkilled if flowering stage occurs prior to the frost.

Roller-Crimper Termination Method

Roller-crimpers (mechanical rollers) are most effective at terminating cover crops by breaking or crimping the stems at flowering stage or later.^4,5 Many cereal grain cover crops and some legumes may be successfully terminated with roller-crimpers. This implement, though heavy, uses about as much energy as a cultipacker and ten times less energy than mowers.⁶

Mowing Termination Method

Mowing is usually not an effective means of cover crop control.⁴ Broadleaves often have multiple growing points and grasses have growing points low to the soil line that would be missed by a mower. Sorghum-sudangrass would be the exception; mowing to a height of two-inches after two feet of growth may terminate this cover crop, as may mowing after heading.⁷ If needed, mowing can be used ahead of tillage to reduce cover crop biomass.

Herbicide Termination Methods

Consider the entire weed control program when selecting chemistry for burndown applications, as cover crops may be functioning in a weed suppression role. For example, in a study published in 2019, cover crop treatments including cereal rye provided biomass to suppress horseweed densities by 56 to 82% compared to a fallow control at the time of spring cover crop termination.⁸ Weed populations could be exposed to selection pressure that encourages the development of herbicide resistance if cover crop biomass intercepts the chemistry. Research from Indiana reported roller-crimped cereal rye intercepted up to 94 and 95% of sulfentrazone and cloransulam-methyl, respectively.⁵

Permissible Herbicide Tank Mixes and Timings

Generally, the herbicide burndown application is most successful for cover crop termination when cover crops are small and actively growing. Additional factors to consider when selecting herbicides and application timings include:

• Cover crops in bolting or jointing stages can be more difficult to control with standard herbicide rates as photosynthate movement—and therefore herbicide translocation—changes for many species by flowering stage.
• Herbicide applications should be made after three to four days of daytime temperatures in the high 50s to low 60s °F, with nighttime temperatures greater than 40 °F.⁹
• Avoid spraying in the early morning, late afternoon, or evening, as plant growth is slower during these times in the spring.
• If glyphosate applications are used, include ammonium sulfate (AMS) at 8.5 to 17 lb per 100 gallons of spray solution as directed by the label.

Herbicides for Spring Termination of Cover Crops

• Radish and turnips. Where winter kill was not effective, apply glyphosate, a Group 9 herbicide, (labelled rate) + AMS + 2,4-D (1 pt/acre). Paraquat is also labelled for cover crop burndown (0.5 to 1.0 lb a.i./acre).¹
• Annual ryegrass. Annual ryegrass growth in the spring should be controlled during early bloom (Figure 1).¹ Apply glyphosate (1.13 lb a.e./acre) + AMS + saflufenacil (0.4 oz a.i./acre) + methylated seed oil.⁴ Note the higher rate of glyphosate. Scout fields after application to confirm complete death of the cover crop. Atrazine and mesotrione should be avoided in the tank mix as they reduce annual ryegrass control by 30 to 50%.³
• Winter wheat, cereal rye, and oats. Apply glyphosate (0.75 a.e./acre) + 2,4-D ester (1 pt/acre) or dicamba (0.5 lb a.e./acre).⁴ If applying glyphosate alone, multiple passes may be needed. Target application timing for early spring during a period of warm weather prior to jointing stage.
• Legumes (crimson clover, red clover, hairy vetch, alfalfa). Apply glyphosate (0.75 a.e./acre) + dicamba (0.5 lb a.e./acre).⁴ Target spray applications for mid-April to first of May for optimum plant activity and herbicide effectiveness.
• Buckwheat. Apply glyphosate (0.75 a.e./acre) + 2,4-D ester (1 pt/acre).⁴ This cover crop can become weedy and should be controlled within 10 days of the start of flowering.¹

Managing Cover Crop Termination Failure

Cover crops may survive herbicide application for several reasons, such as:

• dense cover crop seeding rates
• cold weather during application (nighttime temperatures below 40 °F)⁹
• herbicide antagonism within a permissible tank mix (atrazine has a negative effect on glyphosate activity in cereal rye)³
• lack of ammonium sulfate with glyphosate
• mis-ordered tank-mix order
• the cover crop mix had multiple species, some of which were larger and unsusceptible to herbicide

There is an art to re-termination timing. Dead plant tissue is a poor translocator of glyphosate. Where cool weather was the cause of poor control, consider a two- to three-week wait allowing regrowth and reapplication of a systemic herbicide such as glyphosate with a full spray additive package in warmer conditions. Unfortunately, cash crop planting often doesn’t allow for this luxury of time. Therefore, an application of full-rate paraquat may be applied to burn off the entire cover crop if good spray coverage can be attained with this contact herbicide.

Cover Crop Seed Dormancy

What may look like poor cover crop control could be a natural seed dormancy. Small cover crop seeds could express several dormancy mechanisms resulting in later seed germination in three to 50% of seeds.³ This natural survival mechanism—often found in hairy vetch—can make cover crop control practices appear as a failure or a case of herbicide resistance.^3,4 Continue to scout after termination as cover crop seedings from the previous fall could emerge with favorable conditions after cash crop harvest. In such cases, this should be treated as a new cover crop—not an herbicide resistant, self-seeded, or termination survivor.

In Conclusion

• Cover crop species differ in their ability to survive winter conditions.
• Herbicides are often preferred over tillage as a method for removing an overwintered cover crop.
• Generally, it is best to remove cover crops prior to seed set to help manage the seed bank.
• Termination failures may actually be seed dormancy, with the former requiring special attention to timing chemistry re-applications to active plant growth.

Sources

¹Clark, A. (Ed.) 2012. Managing cover crops profitably (3rd edition). Sustainable Agriculture Research and Education.
²Souza, M., Cooper, E., Cason, E., and Butts, T. 2026. Cover crop termination and timing. Purdue University, Pest & Crop Newsletter. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/cover-crop-termination-and-timing/
³[SARE Outreach] Plumer, M. and Berger, S. 2014. Cover crop management and termination [video]. YouTube. https://www.youtube.com/watch?v=qkDU9X5KP_4
⁴Hill, E. and Sprague, C. 2024. Cover crop termination. Michigan State University. MSUE CC-01.
⁵Oliveira Ribeiro Maia, L., Armstrong, S.D., Kladivko, E.J., Young, B.G., and Johnson, W.G. 2025. Influence of cover crop termination strategies on weed suppression, concentration of residual herbicides in the soil, and soybean yield. Weed Science. 73: 1–11.
⁶Curran, W., Ryan, M, and Mirsky, S. 2026. Cover crop rollers for Northeastern grain production. PennState Extension. https://extension.psu.edu/cover-crop-rollers-for-northeastern-grain-production
⁷2025. Sorghum-sudangrass – cover crop fact sheet for Iowa. United States Department of Agriculture – Natural Resources Conservation Service and Iowa State University. CROP 3247.
⁸Wallace, J.M., Curran, W.S., and Mortensen, D.A. 2019. Cover crop effects on horseweed (Erigeron canadensis) density and size inequality at the time of herbicide exposure. Weed Science. 67:327–338.
⁹Loux, M. 2007. Burndown herbicide activity—Can we kill anything when it’s this cold? The Ohio State University, C.O.R.N. Newsletter 2007-08.
Web sources verified 09/01/2026. 1017_160754