After a cover crop has performed its duty over the winter, deciding when and how to turn it into residue can be a tad complicated.

Some herbicides don’t perform well on certain species, and some species, crimson clover, for example, can be hard to terminate.

Josh Copes, LSU AgCenter, Northeast Research Center, speaking at the annual Louisiana Agricultural Technology and Management Conference in Marksville, La., discussed several recent studies addressing cover crop termination dates and herbicide selections.

Timing might not be as critical a factor as some would think, Copes says. “If you have not been able to terminate cover crops yet, don’t panic, he said at the Feb. 11-13 conference, sponsored by the Louisiana Crop Consultants Association. “The timing of cover crop termination had minimal effect on final crop plant stand, plant height, nematode numbers, or crop yield,” he said.

He says termination date could affect weed populations, however. “Winter weed pressure was significantly reduced by cover crops. Weed pressure was reduced the later the cover crop was terminated.”

Product choice

Product choice for termination does make a difference, he says.

In one study, he reports that a mix with dicamba provided consistent control of legume cover crops, and 2, 4-D was good on hairy vetch. “Elevore and 2, 4-D were weaker on legumes than dicamba. But a mix of Elevore (3/4 ounce per acre, plus 2, 4-D at 16 ounces per acre) provided similar control of legumes as dicamba.”

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He adds that hairy vetch and Austrian winter pea were easier to control than crimson clover.

In a second study, he notes that crimson clover control was better when herbicides were applied in early February.

In that same study, Roundup PowerMax plus Sharpen or 2, 4-D plus Xtendimax provided good control of radish, crimson clover, Austrian winter pea, hairy vetch and cereal rye.

“Glyphosate provided consistent control of cereals.”

He recommends higher rates of glyphosate, 32 ounces of a 5.5-pound active ingredient per acre product or 44 ounces for a 4-pound active ingredient product.

“Gramoxone treatments did not provide consistent control across cereals. Roundup PowerMax plus 2, 4-D did not adequately control crimson clover,” Copes says.

Black oats

He says black oats is a good cover crop option. “I like black oats, it’s easy to kill.”

Crimson clover proved to be a difficult cover crop to terminate, based on trial results. “It’s especially hard to control if you let it get too far,” Copes says. “Paraquat plus metribuzin did not perform well on crimson clover.

He adds that crimson clover control tended to be better when herbicides are applied Jan. 30 compared to March 8.

“Other species appear to be less sensitive to application timing. Austrian winter pea, hairy vetch and tillage radish, Copes says, were not greatly influenced by when systemic herbicide applications were made.

Paraquat plus metribuzin, however, provided good control of Austrian winter pea and hairy vetch applied in March.

“Austrian winter pea is pretty easy to control,” Copes says, “except with Valor. We may see some tolerance to Valor.” Cereal rye control, however, was better with Valor in the mix.

Copes notes that soil temperatures at planting time were cooler compared to no cover.