Heavy Moth Flights Across Midwest Signal Rising Cutworm Risk

With black cutworm moths making their annual migration into the Midwest, agronomists are urging farmers to begin scouting susceptible fields to avoid significant crop damage. Trapping reports from across Illinois, Iowa, Ohio, and Wisconsin indicate increasing moth activity, marking the beginning of a high-risk window for corn.

Flight Monitoring

Trapping efforts begin April 1st and continue through the end of May for black cutworm and armyworm in Illinois and other Midwest states. “This gives us an indication of when moths start arriving and helps us determine potential areas where insect pressure might be a little higher,” said Kelly Estes, Illinois State Agricultural Pest Survey coordinator. 

A significant flight of black cutworm occurs when 8 or moths are captured over a two-night period, explained Estes. “We’re seeing significant flights already,” Estes said. “This serves as the “biofix” for degree day accumulation and indicates an increased risk of injury to corn.” 

Estes noted that large moth captures don’t necessarily mean damage is imminent, but should alert growers to begin scouting three to four weeks after the capture. Monitoring programs, such as  the one Estes coordinates in Illinois, provide critical forecasting tools.

“Our trapping program helps growers know when and where risk is elevated,” she explained. “It’s a forecasting aid. Significant captures mean increased risk, not a guarantee of cutting. Likewise, low trap counts don’t mean you’re safe.” 

Weather plays a major role. “Storms that bring these moths north also influence where they deposit eggs,” said Estes. “That’s why we often see patchy outbreaks—one farm gets hammered, another a mile away doesn’t.”

Scouting for Cutworm

No-till, strip-till or fields with heavy winter annual weeds or cover crops are most at risk for black cutworm, said Ryan Gentle, an agronomy manager for Wyffels Hybrids. “These are the fields you really want to keep an eye on first,” he said. 

The first sign of black cutworm damage is leaf feeding on emerged corn or weeds. Sometimes, larvae will cut weeds before they move to corn. Small larvae create irregular holes in corn seedlings, said Gentle. As larvae get larger, they can cut off corn plants. “Sometimes, they’ll bite a leaf off and you’ll see that corn leaf or stem sticking up out of a hole,” he said. “If you dig, you’re probably going to find a cutworm.”

Cutworms feed at night and hide during the day, so scouting first thing in the morning is the best opportunity to catch them in the act, said Gentle. “It’s important to dig up some cutworms because you need to know the instar size and the stage of your corn to predict the potential for additional cutting.” 

Management

Some Bt traits like Viptera and Herculex provide protection, but many corn hybrid traits offer little or no defense against cutworms, said Gentle. Similarly, standard seed treatments may offer limited control but can be overwhelmed by larger larvae.

Insecticide applications can be effective but require timely scouting. “If you’re not going to scout, it’s worth considering a soil-applied insecticide or using a hybrid with effective traits — especially if you’re in a county with significant flights,” said Gentle.

True Armyworm

Growers should also remain alert for armyworms, which migrate similarly and target wheat and grass crops. While they rarely cut plants like cutworms do, heavy feeding can defoliate fields quickly—especially in cover crop or wheat systems.

As spring planting ramps up, Estes emphasizes that scouting is critical for both pests. “You don’t want to find out too late,” said Estes. “A little diligence now can save a lot of yield later.”

You can track moth flights for black cutworm and armyworm and projected cutting dates for Iowa, Illinois and Wisconsin at the Corn ipmPIPE website. Check with your state Extension service for additional resources.