SDSU Extension Entomologist Mike Catangui said he has found black cutworm infestations while inspecting fields in southeast South Dakota. He added that reports of cutworm damage from central parts of South Dakota may prove to be a different species of cutworm. Reports of cutworm damage to corn are coming from Irene, Scotland, Wessington Springs, Alpena, Highmore, Pierre, Lyman County and Edmunds County.
"It encompasses a wide area," Catangui says. "We might be dealing with two or three species of cutworm."
Larvae of black cutworms can be very damaging because they cut the corn growing points from under the soil. Wilted seedlings, scattered pieces of leaves, and small holes on leaves are common signs of black cutworm infestation.
Cutworms are active at night and hide under loose soil during the day. Scouting during the day involves scratching the soil surface to expose hidden larvae.
Catangui says producers should consider insecticide treatment if 5% (one in 20) of the seedlings show signs of cutting or leaf feeding, and if the larvae are still less than an inch long. Chemical rates and treatments are the same regardless of the species of cutworm.
Insecticides labeled for use against cutworm larvae on corn as seedling foliar sprays include Asana XL (5.9-9.6 fluid oz./acre), Baythroid (.8-1.6 fluid oz./acre), Capture 2EC (2.1-6.4 fluid oz./ acre), Lorsban 4E (1-4 pints/acre), Mustang 1.5EW (1.4-3.0 fluid oz./acre), Pounce 3.2EC (4-8 fluid oz./acre), and Warrior (1.92-3.20 fluid oz./acre). Read and follow all directions on the label.
Dingy cutworms or some other cutworm species may be accounting for some of the damage in area fields, Catangui says. Dingy cutworms overwinter as partially grown larvae in the soil then resume feeding in the spring. Dingy cutworms are not as damaging as black cutworms because they usually cut seedlings above the growing point.
Farmers who are using new Bt corn hybrids with the Herculex I gene will observe that those seedlings are resistant to cutworms as compared to untreated, conventional corn or to Bt corn with the YieldGard corn borer gene, Catangui adds.