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Black cutworms on the move in the Corn Belt

Agriculture.com Staff 05/18/2007 @ 12:13pm

Black cutworm damage has been discovered in Illinois corn fields, some severe enough to meet or pass the economic threshold for treatment.

"It is certainly at a level we've never seen before in certain areas," according to Pioneer Hi-Bred International, Inc. area agronomist Shawn Jones of Colchester, Illinois. Black cutworms at economic threshold levels are being found in fields throughout Illinois, mainly in western parts of the state, Jones said.

"I've seen them now in from the Decatur area to the Quincy area -- across much of west-central Illinois," said Jones. "It's not epidemic proportions, but there are spotty fields with significant populations."

The economic threshold for black cutworms is around three percent cutting damage.

And, with the crop lagging in its development due largely to later planting dates this year, growers are urged to remain vigilant for scouting and treating the pest for the next two to three weeks.

Combined with the corn crop's slow development after moisture-delayed planting earlier in the spring, more frequent southerly winds have likely blown more cutworm moths into the Corn Belt from the southeast, where they're more common, according to Jones.

"If I had to guess, we have had more than our fair share of southerly winds this spring, coming up from the south and bringing that warm air from the Gulf and with that, more black cutworm moths," Jones told Agriculture Online Friday. "We've had, over the last month or so, several significant moth captures. With those moth captures, you can predict when you'll have cutting. That's a good indicator you'll have feeding.

As far as the geographic spread of black cutworms around Illinois, University of Illinois Extension entomologists Kevin Steffey and Mike Gray said this week that infestations are reaching economic threshold levels in several parts of the state. Typically, cutworms are observed in western Illinois, but Steffey and Gray said cutting damage has been reported in southwestern and eastern parts of the state as well.

This spring's later corn planting means the plants are smaller and more susceptible to cutting damage. But more important to the prospects of black cutworm infestations, many fields have more plant tissue in the form of weeds. This green growth attracts the moths, which drop into Corn Belt fields from southerly wind currents.

"Later planting means smaller corn and more weed growth, so we've got greener fields, and those moths are attracted to the greener fields," he said. "If you have winter annual weeds, you have a higher chance of cutworms in the fields."

Steffey and Gray agree. "Most of the black cutworm infestations have been in no-till and strip-till fields or fields with considerable weed cover before planting," they said. But, one example shows it's not just the weedy fields that growers need to be out scouting.

"A field in which cutworms were drilling into the bases of seedling corn plants in Douglas County (Illinois) was weed-free this spring," they said. "This is only one example of the occurrence of black cutworm problems that didn't go by the book, and a strong indication that all fields of corn need to be scouted right now, regardless of the condition of the fields before planting."

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