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Corn+Soybean Digest

Black Cutworms Keep Pressure On Late-Planted Corn

After a brief lull, black cutworm moth activity has resumed in northeastern Missouri, and southeastern Missouri reported its first intensive cutworm capture, said University of Missouri (MU) entomologists.
“Farmers still need to get out there and look at their crops,” said Wayne Bailey, MU Extension entomologist. “Burrower bugs are starting to show up in soybean fields, and it’s getting late enough that we could start having other pests, like green cloverworm, fall armyworm and corn earworm.”

Black cutworms have been prolific this year due to wet weather, heavier weed cover and delayed planting. Late-planted corn is most at risk in northeast Missouri, while late-planted soybeans are most at risk in southeast Missouri.

“There’s still a good bit of soybean planting going on,” said Kelly Tindall, MU field crop entomologist at the Delta Research Center in Portageville, MO. “In the Mississippi and New Madrid river bottoms, we were under water for six weeks in some places. So what should have been planted in April or May didn’t get in until late May or early June.”

Over a three-day period, 91 black cutworm moths were captured in traps by MU Extension field staff at the MU Delta Center, Tindall said. “It’s not unusual for us to get them, but it’s unusual to get them so late in the year.”

Bailey said recent moth flights are probably late flights from the first generation of overwintering black cutworms.

“What we have left are larvae from that original generation that will cut for the next two weeks, and then their threat to corn and soybeans will diminish,” he said. “The second generation rarely goes to field crops, but typically goes to other crops like vegetable crops. The third generation will do the same. It’s really only the first one that goes to corn and soybeans.”

The traditional economic threshold for black cutworm in soybeans is when 20% of the plants are cut, plant stand gaps are greater than 12 in., and live larvae are present.

“But with higher commodity prices right now we can’t stand for much damage,” Bailey said. “Farmers may want to treat their plants earlier. The treatment will be different for every stage of growth.”

When scouting, bear in mind that black cutworms are nocturnal and may be hard to spot in the field. “You may just see plants cut, and then if you dig in the soil you’ll see them,” Tindall said.

Signs of damage often show up on field edges first. “If you can find where they moved in, you can do an isolated treatment and you may be able to save some money that way,” she said.

The predicted cutting date in northeast Missouri is June 24, while cutting is predicted for June 30 in southeast Missouri.

While scouting, keep an eye out for other pests like burrower bugs, which are related to stinkbugs, Bailey said. “These pests will work on soybeans up to the tri-foliate leaf stage. Farmers just need to keep scouting.”

For pest questions or help identifying pest problems, contact your local MU Extension office.

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