Cover crop

With spring planting season fast approaching, it is time to start thinking about terminating cover crops.

There are several different approaches to cover crop termination, but Iowa State University researchers say in most cases cereal rye should be terminated at least 10-14 days prior to planting corn.

“Timing is probably one of the most important things,” says Iowa State University Extension field agronomist Meaghan Anderson. “The last thing most farmers want is for the cover crop to affect the yield of the cash crop.”

The timing is not quite as crucial for termination of a cover crop ahead of soybean planting because soybeans are more tolerant of ground cover.

But timing is also important if farmers are considering the idea of using a residual herbicide with that burndown treatment, says Kevin Bradley, a weed scientist at the University of Missouri. He says a residual can work if the farmer is killing knee-high cereal rye two to three weeks before planting. But if the burndown comes later when the cover crop is taller, the residual treatment is less effective.

Anderson says herbicides offer the most flexibility and consistency in cover crop termination, and for cereal rye glyphosate is often the most forgiving option. But she says paraquat may also work in certain situations. Neither group 10 (glufosinate/Liberty) nor group 1 (Assure II, Select) herbicides have provided consistent control of cereal rye.

And farmers looking to avoid chemical treatments can get good results by roller crimping. If using a roller crimper before soybeans, Anderson says it helps to first let the cover grow and head out.

There are some useful tips that should be considered when planning spring cover crop termination, she says.

Whenever possible, spray in the middle of the day in sunny conditions when daytime temperatures are above 60 degrees and the cover crop is actively growing. Overnight lows should be above 40 degrees.

Another tip is to avoid skimping on herbicide or adjuvant rates during cool springtime conditions.

Third, follow herbicide label instructions for appropriate adjuvants, mixing order and application instructions. Increased spray volumes may help improve coverage in dense canopy situations.

Also, the use of off-label adjuvants and the inclusion of additional herbicides may reduce spray efficacy. This can vary depending on the tank mix used.

And it is important to check herbicide labels for restrictions to planting corn or soybeans following the herbicide application.

Anderson says that while a contact herbicide such as paraquat can work, the risk factor is higher and the product is more restrictive than glyphosate.

Gene Lucht is public affairs editor for Iowa Farmer Today, Missouri Farmer Today and Illinois Farmer Today.