By Blake Jackson
Corn growers in southern and central Wisconsin should begin monitoring for black cutworm (BCW) damage starting May 21. This pest poses a threat to young corn plants, especially when larvae reach the fourth instar or higher, cutting plants at the base and reducing yield.
Black cutworm larvae begin by feeding on weeds and corn leaves. As they mature, they can cause serious crop losses by cutting the plant below ground level. Effective scouting is key to early detection. Walk in a W-shaped pattern across fields and inspect five sets of 50 corn plants (250 total). Note how many have been cut and collect two larvae to identify the instar, which helps estimate future damage.
Scouting should continue for two to three weeks after corn emerges, or until the crop reaches the V5 stage, when plants are better able to resist feeding.
A treatment is recommended if 2% to 5% of plants are cut—that’s 5 to 12 out of 250 plants. It's important to note that moth captures, not plant damage, guides the best time to scout, not treat.
Integrated Pest Management (IPM) is the best approach to controlling BCW. This includes removing weeds early to reduce egg-laying sites and encouraging natural predators like birds and insects. Insecticides should be used only if the damage exceeds thresholds and never as a preventative method.
Farmers can learn more from UW-Madison’s black cutworm resource and use degree day models for risk assessment. They are also encouraged to sign up for DATCP’s pest alerts and the Field Notes newsletter for regular updates throughout the growing season.
Photo Credit: gettyimages-oticki
Categories: Wisconsin, Crops, Corn