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Terminating Cover Crops

By: Kacey Birchmier

When it comes to cover crops, priorities are set around seeding methods and potential benefits.
However, equal thought should go into their termination. Improperly terminating a cover crop is a surefire way to have a poor experience with cover crops. Furthermore, it could potentially hurt the following cash crop.

Execution is key to a successful program.
“You have to have a plan A and a plan B for the way you’ll terminate the cover crop before you put it in the ground,” says Rachel Halbach, agronomist at Hagie Manufacturing. “Who knows what Mother Nature will bring in the spring. Hopefully, you only have to use plan A – whether it be a herbicide, crimping, mowing, or tillage.”

A backup plan will make you aware of your capabilities, and you’ll have a definite plan for termination.

“Management is one of the keys, in my opinion, for terminating cover crops,” says Cameron Mills, a no-till farmer from Walton, Indiana. “Determining a plan ahead of time is number one and key. Know your own abilities.”

If you don’t have a sprayer, consider other termination methods. Or, factor into the equation that you’ll need to hire someone to terminate the cover crop (factors that can be easily overlooked).
“Some of these cover crops you’re going to choose from will overwinter,” says Mills. “Knowing that about them is going to be very critical.”

Terminating tips

Halbach lists several cover crop termination factors you need to remember.

  • Select a herbicide that will kill the cover crop.
  • Know your planting restrictions. This means you need to think about the following cash crop and if the selected herbicide might negatively affect it. For a safe bet, either use a product labeled for burndown or preplant for the following crop. 
  • Spray the cover crop with the proper herbicide rate. Consider the height and growth stage of the cover crop.
  • Watch the weather. Mother Nature determines a large portion of successful termination. “In terms of glyphosate, my recommendation is that you need three consecutive days of no cooler than 45°F. temperatures and daytime temperatures of 55°F. to 60°F.,” says Halbach.
  • Decide between contact herbicides vs. systemic herbicides. “If using a contact herbicide, coverage is very important,” says Halbach. “You need 100% coverage of that plant for it to die.” 

Options
Winterkill is often considered training wheels for cover crops, a termination tool for beginners.
For cover crops to winterkill, the temperatures need to stay in the neighborhood of 15°F. for several days, says Tracy Blackmer, research director for Cover Crop Solutions. The maturity of different cover crops will also be affected when they are winterkilled.

“The radish’s growing point is on top of the tuber,” says Blackmer. “If you have a smaller radish, it’s better protected. The more mature radishes are more vulnerable to winterkill than the smaller ones.”

Blackmer suggests considering your location before deciding if winterkill is a viable option for your operation. A good reference is where you live in correlation to Memphis, Tennessee. If you live north of Memphis, odds are winterkill will be an ideal option. If you live south of Memphis, the temperature may not drop low enough for a long enough period of time to rely on this option. Another important factor to remember is allowing adequate time for growth before the average frost date.

Herbicide applications

Herbicides are commonly used in early spring to terminate cover crops, but you’re left at the mercy of the weather. Cold, wet conditions can impact the success of those applications, says Blackmer.

“You have to be really careful that you follow all of the rules that most people ignore,” says Blackmer.

Efficient herbicide applications will rely on the following two guidelines:

  • Don’t spray past 2 p.m. Cover crops aren’t as sensitive to termination herbicides starting in midafternoon and into the evening. Midafternoon and evening applications won’t kill the cover crop, he says.“It will make it so it’s less sensitive, and it creates a mess,” adds Blackmer.
  • Wait two weeks for the cover crop to die. That’s the amount of time it takes for cover crops to die after a proper application. This means you won’t know immediately if your application worked.“If you try to terminate two weeks before planting corn and it hasn’t fully died, that’s a problem,” says Blackmer.

One solution for those opting to kill the cover crop with a herbicide application is to plant corn with the LibertyLink or Roundup Ready traits, says Blackmer. Those traits provide a safety net that allows additional application to be made without crop injury. Blackmer says to avoid herbicides with residuals if you plan on interseeding, since it could interfere with germination or early growth.

Mechanical Methods

Another option is termination from mechanical methods, but that depends on your species, says Blackmer. It’s these issues that you need to be aware of before selecting a cover crop species.
“A roller crimper or another nonchemical method won’t work on annual ryegrass,” he points out.
Crimping, mowing, or tillage are mechanical options that Halbach recommends.

It’s important to know that the cover crop program you pick fits your equipment and program, says Mills.

Two rules of thumb
Termination should occur two or three weeks before planting corn. If planting soybeans, though, you can terminate the cover within three to four days after planting, says Blackmer.

Part of the planning process is to be in compliance with your crop insurance.
“To be compliant with crop insurance, you need the cover crop killed before a specific date – there’s a time spread between termination and planting,” says Blackmer.

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