Potential for Black Cutworm Problems Still Exist

Published: May 19, 2009

Problems with black cutworm continue to be reported, although numbers of infestations statewide are lower than in past years. Although limited numbers of black cutworms may overwinter in Missouri in some years, a majority of infestations originate from moths migrating into the state on the front side of early spring storms which originated from sites along the Gulf Coast and Mexico. Female moths will lay up to a 1,000 eggs either singularly or in masses of up to 30 eggs on a variety of vegetations and occasionally on plant residues. Larvae vary from light gray to black in color and grow to 1 ½ - 2 inches in length. A total of 6 to 7 worm stages or instars are produced with instars 1-3 feeding on leaf tissue and instars 4 -7 cutting plant stems as well as feeding on foliage. When disturbed, the larvae will curl into a "C" shape and play dead until the danger has passed. This insect produces 3 generations annually with 35 – 50 days required to complete a generation (egg to adult). The black cutworm is a general feeder with the first generation often attacking the field crops of corn, sorghum, and occasionally wheat. Later generations are often responsible for problems in turf and vegetables.

Late planted corn is most at risk from black cutworm larval attack. Small seedlings are most heavily damaged by large worms. As larvae have grown in size during the past few weeks, small recently emerged corn seedlings will sustain severe damage if a black cutworm infestation is present. Damage is often restricted to low areas of the field which contained lush vegetation during the time eggs were being deposited, although some fields will have larval infestations throughout. Producers are encouraged to scout fields several times per week to determine the presence and level of black cutworm infestations. As corn plants reach the 4-leaf stage they are less likely to be attacked by this pest. Economic thresholds for black cutworm infestations vary by field, plant size, and insect size and number, but generally treatment is recommended if 1-2% or more of plants are cut below ground and 2-3% or more of plants are cut above ground. Above ground cutting is less serious as the growing plant is left undamaged, in contrast to being damaged when plants are cut underground. Seed treatments will provide some control, but may not prevent an infestation from reaching or exceeding economic threshold levels. The risk from black cutworm larval damage to seedling corn will continue for about another two weeks. The following list of insecticides is recommended for black cutworm larval control on field corn.