Cover crops have many benefits, including suppressing weed emergence and growth. Planting soybeans in a standing cover crop and then terminating the cover crop stymies weeds without harming yield. Corn, however, is a bit trickier. Competition from the cover crop can reduce corn yield. In addition, failure to kill the cover crop in a timely manner and improper nitrogen management will result in fewer bushels. 

“If your weed suppression goal with cereal rye ahead of corn is reducing winter annual weeds, that can be successful when you burn down the rye in a timely manner ahead of corn planting, so it doesn’t compete,” says Meaghan Anderson, Iowa State University Extension (ISU) field agronomist.

“But if you’re targeting suppression of a later-emerging weed like waterhemp, you’d need a thick biomass cover that lasts into late June. And if you’re planting corn the third week of April, there’s no way rye could grow to that size without sacrificing crop yield,” she adds. “Soybeans can tolerate taller rye, but corn needs space from another grass.”

Managing Rye the Right Way

Using cover crops as a potential method to save on herbicides has gained interest as input costs rise. Anderson recommends following best management practices to control weeds in corn planted into cereal rye. That means terminating rye at least seven days before planting, ensuring available nitrogen at planting, and scouting for pests.

According to Iowa Soybean Association (ISA) research, the challenge is ensuring the cereal rye is terminated by 8 to 12 inches in height, so it doesn’t impact corn yield. “There’s not a lot of farmers taking the risk of letting cereal rye get too big in corn,” Anderson says. “But farmers in southeast Iowa, for example, are doing it where they have a conservation culture and a mindset to make it work.”

These growers have a deep passion for no-till and cover crops. They’re making cover crops in corn work — from letting the cover crop grow tall before terminating it to interseeding multispecies cover crops in corn. “The majority are still terminating the rye early ahead of corn, but they’re used to doing things differently and testing to make these practices work,” Anderson adds.

Preventing yield loss in corn planted into cereal rye also depends on nitrogen management. In a previous story that appeared on the Corteva Agriscience The More You Grow webpage, “Grow Cover Crops in Corn Without Yield Loss,” an ISA researcher discussed the importance of planning available nitrogen before the V6 growth stage when using cereal rye ahead of corn. Early season nitrogen applications with the planter, early sidedress and post-planting broadcast applications of urea plus AMS provided a 10- to 20-bushel-per-acre advantage compared with no cover crops.

Other Options

What about other cover crops? Anderson cites University of Nebraska research using a hairy vetch cover crop ahead of corn that suppressed weeds in-season without losing corn yield compared with no cover crops. “I would suspect their observed weed suppression levels would still not change the herbicide program,” Anderson says.

While cover crops likely won’t replace a corn herbicide application, they can make weeds easier to control. “We know that cover crops can reduce the weed population and delay weed emergence. That benefit gives growers a bigger window of opportunity to treat them in a timely manner,” she says.

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