Terminating Cover Crops: When, Why, and How?

Cover crops should be terminated in a minimum of 10 days to 4 weeks before planting a crop (2 weeks is a good rule of thumb). 

Corn:

Competition for nutrients and moisture, along with allelochemicals given off by cover crops, can decrease corn yields if they are terminated less than two weeks before planting. 

Soybeans:

Soybeans are less influenced by these yield-limiting factors, especially with a small grain cover crop. However, soybeans are more at risk from insect pests moving from the cover crop if it is terminated at or after planting. 

📸: BASF employee, D. Waldstein/Featuring an example of terminated cover crops.

Why Delay Termination?

The primary advantage of delaying cover crop termination is greater biomass production, which can aid in early-season weed control and add more organic matter to the soil. 

Why Terminate Early?

Terminating small grain cover crops by flag leaf will decrease the amount of nitrogen that is tied up in the cover crop. Dry conditions may push the decision in favor of early termination to keep soil moisture from being depleted.

Mechanical only option:

If you use the mechanical only option to terminate a cover crop, it is necessary to wait until the small grain flowers (soft dough stage is best) so the roller/crimpers will successfully lay the cover crop flat to the ground.  

📸: BASF employee, A. Hixson/Featuring an example of cover crops.

Which Herbicide to Choose?

Glyphosate is generally the most effective herbicide used for termination of cover crops. Adding Sharpen^® herbicide, 2,4-D, or clethodim can increase the effectiveness of termination (Whalen et al. 2019). 2,4-D should be added to glyphosate if legume species (e.g., clover, hairy vetch, winter pea) need to be terminated. Remember to apply the glyphosate on warm, sunny days. 

Glyphosate Rates:

Cereal rye (22 oz), legumes (33 to 44 oz), winter wheat/annual ryegrass (44 oz).

📸: BASF employee, D. Waldstein/Featuring Red clover + cereal rye cover crop, March 1, central North Carolina.

Potential Pitfalls:

If the cover crop is still green at corn or soybean planting, it can increase the “hairpinning” phenomenon, which may pull the residue into the seed furrow and decrease seed-to-soil contact at planting. After the herbicide application and before planting, mechanical roller/crimpers can be used to lay the residue flat. A standing cover crop has a greater likelihood of causing problems by wrapping around coulters, shanks, or discs.  

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Endnotes 

1. https://agcrops.osu.edu/newsletter/corn-newsletter/2020-05/cover-crop-termination
2. https://www.sare.org/publications/conservation-tillage-systems-in-the-southeast/chapter-5-cover-crop-management/termination-of-cover-crops/
3. https://www.nrcs.usda.gov/wps/portal/nrcs/ia/newsroom/features/STELPRDB1086071/#:~:text=Producers%20can%20terminate%20cover%20crops,them%20without%20tilling%20the%20soil.
4. https://www.ars.usda.gov/ARSUserFiles/66120900/Reeves/ReevesAuburn/ashford_00a.pdf
5. https://soybeans.ces.ncsu.edu/2021/03/pfp21-think-about-pests-when-terminating-cover-crops-prior-to-planting-soybeans/#:~:text=For%20this%20reason%2C%20termination%20timing,injury%20to%20the%20soybean%20crop. 
6. Whalen D, Bish M, Young B, Conley S, Reynolds D, Norsworthy J, Bradley K (2019) Herbicide programs for the termination of grass and broadleaf cover crop species. Weed Tech 34: 1–10

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