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Herbicide Carryover Could Hurt Cover Crops

Farmers who planted cover crops last fall need to terminate them before planting corn or soybeans, says a University of Missouri Extension weed specialist.

Kevin Bradley, who has done a lot of research on killing out different types of cover crops, says timeliness is key.

“They are going to start busting out here with the weather we are having and really start to take off and get a lot of growth on them,” Bradley says.

Without effective control, cover crops can in effect become weeds and impact corn or soybean yields.

“If a ryegrass greens back up, that is going to take nutrients and water away from the crop that we want,” Bradley says. “That’s why we need to get in there early and burn those down.”

If producers intend to plant cover crops after corn or soybeans, they need to carefully consider what herbicides to use on their row crops. Some active ingredients in herbicides can carry over in the soil and injure cover crops that may be seeded later in the summer or in the fall.

According to Bradley, research has shown that fomesafen, the active ingredient in Flexstar and Prefix, can damage a lot of the broadleaf winter annual cover crops, while pyroxasulfone, found in herbicides such as Zidua, can injure some of the grass cover crops.

“It’s a pretty complex issue and you need to look at the active ingredient and the cover crop species you want to plant,” Bradley says. “You have to think about that now as you’re planning your weed control program this season.”

More information on herbicide injury is at http://weedscience.missouri.edu/herbinjury.cfm.

Source: University of Missouri

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