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Posted 16 May 2008. PMN Crop News.

Black Cutworm

University of Illinois at Urbana-Champaign.

Urbana-Champaign, Illinois (April 29, 2008)--Delayed corn planting, storm fronts, and actively growing weeds are indicators that black cutworms could be more of a widespread problem this year than in the past few years.


Storm fronts carry adult black cutworm moths to Illinois. Female moths "drop out" of these storm fronts and seek attractive egg laying sites, such as winter annuals and perennial weeds. As planting is delayed, black cutworm larvae (worm) will hatch and begin feeding on the weeds. As the weeds are killed, the cutworms need additional food and will be large enough to cut corn plants as seedlings emerge from the soil. Black cutworm moths have been caught in pheromone traps in Lee, Ogle, Whiteside, and Winnebago counties. Intense captures (nine or more moths captured in one or two days) have been reported in Ogle County on April 17 and 18. Degree-days can be an effective tool to help determine when to start scouting for black cutworm larvae. Black cutworm larvae are expected to begin cutting corn with the accumulation of approximately 300 degree-days, base 50 degrees F, after an intense capture occurs. Cutting dates for your area can be predicted by using the Degree-Day Calculator at the University of Illinois IPM ( and WARM ( websites. Early signs of cutworm feeding are pinholes in the leaves of newly emerged seedlings. This initial damage is not economic and can occur before 300 degree-days have accumulated. But, it is a precursor to stand-reducing cutting damage. If tillage or herbicides eliminate weeds one to two weeks before planting, black cutworms that had been present probably starve to death. The presence of weeds only a few days before planting increases the likelihood of cutworm damage if larvae are present in the field. Early season scouting for black cutworms is essential, even if products for control have been used. Cut, missing, or wilted corn plants are typical symptoms of black cutworm larvae damage. Feeding mainly at night, larvae will move up the row as they feed. On average, one larva may cut three or four plants in its lifetime. Postemergence rescue treatment is suggested when 3 to 5 percent or more of the plants are cut and larvae present. One should also consider the location of the cutting (above or below the growing point), size of the cutworm, and soil moisture conditions. Rescue treatments for black cutworms are listed in the 2008 Illinois Agricultural Pest Management Handbook. Be sure to read and follow label directions. Further information on this pest is available at this University of Illinois website:, or contact your local Extension office.