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COLUMBIA — Missouri farmers should keep checking cornfields for damage from black cutworms.
Late moth flights into several parts of the state have helped the insect remain a threat to still-emerging cornfields and fields that farmers need to replant, said Wayne Bailey, a University of Missouri Extension entomologist.
“Some years we’ll just get one or two moth flights, but this year we’ve been getting a low level of moth flight consistently throughout the spring in some locations,” Bailey said. “We certainly have them in northeast Missouri and have seen populations between Columbia and St. Louis and others along the western border this year.”
Extended moth activity means a longer period of impact on young corn. Coupled with the need to replant fields where excessively wet weather caused poor stands, farmers might see a resurgent impact late in the season.
“Now there are many different stages of black cutworm larvae in fields, so if you planted late or are replanting corn in the next week or two, you are still going to have larvae around in the fourth, fifth and sixth stage, which are the life stages that cause the most damage to corn,” Bailey said.
Recent hot weather is pushing small larvae quickly toward maturation, he said. “We’ll be seeing acceleration in black cutworm size. With replanting there’s truly potential for damage and they really need to be watching.”
Farmers need to pay attention to more than just immediately visible damage.
While black cutworms can damage the aboveground plant, cutting below the surface can have a bigger effect on the health of a cornfield. Wet weather has further reduced resistance to the insect because seed treatments often wash away under heavy rain.
“Scouting is pretty important to know what is out there. It could be in one area of the field or be an overall problem,” Bailey said. “Our best recommendation is to be out in the field every three days checking for problems, and if you see 2-3 percent underground cutting or 3-5 percent aboveground cutting before the four-leaf growth stage, you need to think about a rescue treatment.”
If farmers remain watchful for a few more weeks, black cutworm will cease to be an active problem and they can focus on other things, he said.
For more information, see the MU Extension publication “Black Cutworm in Missouri” (G7112), available for purchase or free download at http://bit.ly/MU ExtCutworm.