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Time to look for black cutworms

A warm, wet spring has laid the groundwork for black cutworm feeding in corn. Here’s what you need to know, what to look for and what to do about it.

Holly Spangler, Prairie Farmer Senior Editor

May 21, 2024

3 Min Read
A black cutworm lying on soil next to a plant
SEARCH: To find black cutworms during the day, use a knife to dig through debris. If you have moist soil, cutworms may be closer to the surface, but if the soil is drier, you may have to dig deeper to find them. Purdue University

It’s been a warm, wet spring, and that could mean peak feeding conditions for insects like black cutworm.

“Initial feeding occurs when small larvae feed on plants, and you’ll see small, irregular holes in the leaves. As the larvae begin to grow, they will actually turn more to cutting a plant,” says Kelly Estes, coordinator of the Illinois Cooperative Ag Pest Survey Program. At that point, you can look down a corn row and potentially see several plants missing.

Estes says the pest survey program began observing black cutworm moths in traps in late April.

The survey has a network of traps across the state, and they develop a map of feeding predictions based on the findings. Nine or more moths caught over two nights count as a significant flight, and they use degree-day predictions to calculate potential dates that larvae will hatch and eat. Several counties already have observed cutting.

Estes says sustained flights throughout the spring, combined with wet weather and a prolonged planting season, mean farmers may see a longer, drawn-out black cutworm feeding season — with multiple life stages of cutworm.

Even if your county didn’t record significant moth flights, you can still see feeding and injury in corn.

Check out this county-by-county black cutworm map from the regional Integrated Pest Management centers, regularly updated with new data from universities nationwide, including the University of Illinois. You can also stay informed about other pests, including corn borer, earworm, armyworm and western bean cutworm.

Black cutworm scouting tips

What to know about black cutworms:

  • Moths migrate north from Gulf states into the Midwest from March through May.

  • Moths enjoy fields with heavy infestations of weeds like chickweed, shepherd’s purse, peppergrass and yellow rocket.

  • Late tillage and planting tend to make fields more susceptible to black cutworm infestations.

  • Larvae start feeding at their fourth instar stage; a single cutworm can cut three to four plants as it grows.

  • To find cutworms during the day, use a knife to dig through debris. If you have moist soil, they can be closer to the surface, but if the soil is drier, you may have to dig deeper.

  • Feeding usually happens at night or on dark overcast days.

  • Fields at most risk of economic damage are in the one- to four-leaf stage.

  • Look for small pinhole feeding injury in leaves; don’t wait for cutting to take place.

  • Not all Bt hybrids offer the same level of cutworm protection. Michigan State University offers The Handy Bt Trait Table to help determine protection levels.

What to do if you find black cutworms:

  • If you find 3% cutting of plants, consider a rescue treatment.

  • Spot-treating may be sufficient.

  • If cutworms are bigger or later instar larvae, they’re nearly done feeding and cutting. You may be ahead to wait it out and replant those spots instead of applying an insecticide.

  • After plants are past the V4 stage, they’re at less risk of injury.

Want to know more? Check out the University of Illinois Crop Sciences fact sheet on the biology, life cycle and management of black cutworms. For questions about black cutworm, contact Estes or Nick Seiter, U of I field crops entomologist.

Read more about:

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About the Author(s)

Holly Spangler

Prairie Farmer Senior Editor, Farm Progress

Holly Spangler has covered Illinois agriculture for more than two decades, bringing meaningful production agriculture experience to the magazine’s coverage. She currently serves as editor of Prairie Farmer magazine and Executive Editor for Farm Progress, managing editorial staff at six magazines throughout the eastern Corn Belt. She began her career with Prairie Farmer just before graduating from the University of Illinois in agricultural communications.

An award-winning writer and photographer, Holly is past president of the American Agricultural Editors Association. In 2015, she became only the 10th U.S. agricultural journalist to earn the Writer of Merit designation and is a five-time winner of the top writing award for editorial opinion in U.S. agriculture. She was named an AAEA Master Writer in 2005. In 2011, Holly was one of 10 recipients worldwide to receive the IFAJ-Alltech Young Leaders in Ag Journalism award. She currently serves on the Illinois Fairgrounds Foundation, the U of I Agricultural Communications Advisory committee, and is an advisory board member for the U of I College of ACES Research Station at Monmouth. Her work in agricultural media has been recognized by the Illinois Soybean Association, Illinois Corn, Illinois Council on Agricultural Education and MidAmerica Croplife Association.

Holly and her husband, John, farm in western Illinois where they raise corn, soybeans and beef cattle on 2,500 acres. Their operation includes 125 head of commercial cows in a cow/calf operation. The family farm includes John’s parents and their three children.

Holly frequently speaks to a variety of groups and organizations, sharing the heart, soul and science of agriculture. She and her husband are active in state and local farm organizations. They serve with their local 4-H and FFA programs, their school district, and are active in their church's youth and music ministries.

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