Best practices for terminating your cover crops this spring

Knowing when and how to best terminate cover crops is crucial to ensure you start the year off right, and on time.

Making decisions around when and how you terminate your cover crop is dependent on your goals for the cover crop. Although we have the added factor of chemical costs to consider this year, the best practice is to stick to your pre-existing plan and have a backup plan in place. It's better to be a little early than to be too late and miss your window for successful termination.

Crucial cover crop watch: Terminating grasses prior to corn. The more mature the rye, the higher the C:N ratio will be. This will lead to it competing for nitrogen which will, in turn, stunt your corn.

When do I terminate?

In most cases, I recommend either terminating two weeks prior to planting or at planting - there are positives and negatives to both. The safer bet is terminating two weeks prior to planting so that the cover crop completely dies off. If you are forced to plant green, do not panic and till it all up as this will likely make a bigger mess than if you had just planted. Take your time to set your equipment right, especially on your first few fields. This will slow you down initially but once you are set you should be able to keep on moving.

Major misconceptions that can trip you up:

"Cover crops make soil colder and wetter so kill them early."    

Not so fast. Cover crops and reduced tillage protect your soil by insulating it and buffering temperature swings. These practices ensure that during the cold snaps in spring, soil will be warmer, and during the hottest parts of the year, soil will be cooler. This means plants are less stressed and therefore use less water. Terminating these cover crops too early (three weeks or more prior to planting) can prove both myths:

  1. In wet conditions, you take away a plant that was transpiring water from the soil to the atmosphere and instead leave a wet mulch on the soil surface which will push planting dates even later into the season.
  2. In drier springs*, the mulch left behind after termination can protect the crop and soil from evapotranspiration.

*In cases of extreme spring drought, it may be advised to terminate earlier if there is concern for moisture competition. In most cases cover crops aid in water retention from better soil aggregation, increased infiltration, increased soil organic matter (which acts like a sponge), and soil protection.

How do I terminate?

There are several methods for cover crop termination including chemical, mechanical, and species selection (winter kill). We will focus on chemical and mechanical for now.

Chemical Termination

Chemical herbicide is the most popular tool for cover crop termination. In most years chemical is fairly affordable and easy to terminate quickly. However, this year is a different story. Rising chemical costs mean you must be targeted and intentional about your applications.

  • Do not cut rates. If you don't get a complete kill you will have to apply again and spend more money.
  • Buy generic. You can find potential alternatives to glyphosate here and here.
  • Prioritize using glyphosate when terminating grass cover crops and find alternatives or tank mixes for broadleaf weeds.
    • Combining grass herbicides with broadleaf herbicides can result in an antagonistic effect (poor control). For example, using clethodim with 2,4-D or dicamba. Additionally using atrazine or metribuzin with glyphosate can cause antagonism and very poor control of annual rye grass.

As a general rule, apply systemic herbicide early in the day on still, warm, sunny days (between 9 am and 3 pm to allow for penetration). Apply before the reproductive phases of cover crops, especially grasses. Contact herbicides, like paraquat and glufosinate, can be used in cooler spring situations but make sure you get complete coverage.

Mechanical Termination

Mechanical termination is very popular in organic production and in cases where strong weed protection is desired. This type of termination is usually done with cereal rye and at boot stage (the head is swollen in the stem of the plant) when planting soybeans. It is usually done at least three weeks prior to planting.

While mechanical termination isn't as common as chemical termination, it can still be an effective method especially for tough to control weeds.

Considerations:

  • When planting green, scout your field early and watch for strong fungal or pest pressures.
  • Remember herbicides with long residuals which are applied late in the season may impact growth of cover crops planted after harvest. This can be easy to forget and impact establishment for next fall.
  • If you have a federal contract you must abide by their guidelines, find more here.
    • "For crops planted in the 2020 crop year and later, insurance will now attach at time of planting the insured crop and cover crop management practices will be reviewed under Risk Management Agency (RMA) rules for Good Farming Practice (GFP) determinations similar to other management decisions (e.g. fertilizer application, seeding rates, etc.)"    

Anna Teeter

Anna Teeter recently joined Cargill as Conservation Agronomist with Cargill’s regenerative agriculture program. Her goal is to help farmers successfully implement soil health practices while continuing to advocate for agriculture. Anna brings extensive hands-on experience having worked with the University of Wisconsin-Madison extension services, private ag consulting services, and most recently the Soil Health Partnership, which led her to Cargill. She has a Bachelor of Science in Agronomy and Life Sciences Communications from the University of Wisconsin-Madison and a Masters of Science in Soil Science.

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