Cover Crop Termination Timing Tradeoffs: The warmer spring soil and air temperatures until this weekend have allowed small grains like rye, wheat, and triticale to gain quick growth. A small grain cover crop can impact corn and soybean in several ways including: reducing soil erosion, tying up nitrogen, reducing soil moisture prior to planting, increasing insects (beneficial and pests), reducing weed pressure (either via allelopathy towards small weed seeds or choking out weeds), and reducing soil-borne pathogens that cause soybean diseases. Termination timing is often a question. While I’m a fan of planting green, that doesn’t fit each farmers’ goals or situations. The following are things to consider for termination timing.

Termination prior to planting may be of interest to those who are concerned about soil moisture, who are new to cover crops, who have a subsurface drip irrigation system, or are not allowed to plant seed corn green.

One consideration if terminating prior to corn or soybean planting is to consider using clethodim as it doesn’t die as quickly, allowing for longer-lasting erosion and weed control. We’ve been using 10 oz/ac of clethodim. If you do choose to use clethodim vs. glyphosate prior to corn planting, it needs to be applied at least 7 days prior to planting corn. There are no restrictions with soybean.

Termination at or after planting (planting green) is an option for those who want more cover crop biomass for erosion and for weed and disease suppression. When planting soybeans green, the goal is often to off-set the PRE herbicide cost with the cover crop seed and application cost. Reality is, if you’re going to lie awake anxious about this decision, planting green may not be for you. Often, corn plants will not look as good the month of June, but things often turn around come July.

The following are things to consider as there’s more risk involved. Apply nitrogen as a starter or 2X2 with corn when planting green to help with nitrogen tie-up. Some prefer to wait for the corn or soybean seed to germinate before terminating the cover crop while others terminate the same day as planting. If irrigation is available, have the irrigation system ready to go prior to planting in the event you need to add some moisture into a dry seedbed. Upon planting the field, observe if any adult wheat stem maggot flies are present, and also for the presence of beneficial insects before automatically adding any insecticides in with the herbicide.

Termination of rye occurred closer to heading when wanting greatest biomass in soybean. Roller crimping for termination occurs around pollination. When rye is greater than 12”, consider 15-20 gal/ac of carrier for better coverage. A residual herbicide is helpful at some point. Plan on 0.5-1” of irrigation or rainfall to get the residual to the ground, especially on rye taller than 12”. Some add the residual in with the product used for termination, while others prefer to spray the residual in a second pass once the cover starts dying. Those applying a residual at termination time had irrigated fields and planned on 0.5” irrigation after the rain-fast period. If no rainfall was received in 7 days, they often planned on another 0.5” of irrigation to help move residual down to the soil.

With the quick growth this year, it may be wise to have a Plan A and Plan B in mind if you plan on planting green but the cover crop is getting taller than you are comfortable with, especially for corn. For example, Plan A may be that you’re planning on planting green unless the cover is X inches tall by a certain date (ex. April 5-15), upon which you will choose to terminate pre-plant instead (Plan B). There’s no one size fits all approach, so feel free to call and talk through this if you prefer.

Additional Resources:

Photo gallery from farmers’ fields: https://jenreesources.com/2022/04/03/cover-crop-termination-including-planting-green/

Cover Crop Termination Tradeoffs: https://cropwatch.unl.edu/2021/cover-crop-termination-tradeoffs