Late Planted Corn Susceptible to Black Cutworm

Published: April 13, 2010

One insect which benefits from late planting of corn is the black cutworm. Moths began migrating into Missouri about two weeks ago. Upon arrival, female moths will lay eggs on a variety of vegetative materials and soil surfaces although winter annuals such as henbit and chickweed are favored egg laying sites. Black cutworm grow through several larval stages as they develop from eggs to an adult moth. Smaller instars will often leaf feed causing minor defoliation of corn seedlings, but damage increases significantly as the larvae grow to 4th instar or larger stages and begin cutting plants. A predictive model is used to predict the different developmental stages for BCW. The model is based on intensive captures of moths during early spring and uses both a 30-year average of meteorological data along with real time data collected from several weather stations located throughout Missouri. The predicted date of first cutting may change by location as current 2010 meteorological data are entered into the model.

Scouting activities should occur from first emergence of corn plants and continue through the 5th leaf stage of plant development. If this is not possible, then scouting of fields should begin a minimum of one week prior to the predicted date of cutting. Early damage by black cutworm larvae smaller than 4th instars may be visible as leaf feeding on corn plants. Recent high moth captures in the Columbia and Centralia areas suggest that black cutworm may be an important pest of corn this season.

For more information on the black cutworm predictive model and the counties currently monitoring for black cutworm, please visit our Website at: https://ipm.missouri.edu/pestmonitoring/index.htm. Information at this site will include the number of moths captured, the date of an intensive moth capture (begins the model), and the predicted date of first black cutworm cutting of corn. At present, the predicted cutting for Columbia and Centralia areas is May 2, 2010. This is the predicted date larvae will reach the 4th instar stage and begin cutting plants. This date may change depending on actual meteorological data collected over the next couple of weeks.

Black cutworm infestations may occur in scattered areas within a field or be found throughout the entire field. When scouting be sure to check all areas of the field, but focus some effort on those areas of the field where black cutworm infestations have been found in the past. Although the economic threshold for black cutworm varies from state to state, under normal conditions in Missouri treatment is recommended when cutting of corn seedlings reach or exceed 3-4% cutting above ground and 2-3% cutting below ground. These thresholds are based on the location of the plant growing point at the time of cutting by black cutworm and the potential for yield loss. Cut plants may be left on the soil surface or partially pulled into the soil by the larvae. If the economic threshold is reached, then treatment with a recommended insecticide is justified. It is possible for a field of corn to be infested more than once by black cutworm due to migratory patterns of arriving moths. Corn fields most at risk from this pest are those late planted and have a history of winter annual weeds in the field. Scouting for this pest on seedling corn should begin with emergence and continue through the 5th leaf stage of plant development. Rescue applications of labeled insecticides generally provide control of this pest. Seed treatments will provide partial control of this pest, but heavy populations of larvae may cause significant damage in seed treated fields. The Herculex event along with several transgenic events currently undergoing labeling have been shown to provide good control of black cutworm in Missouri field trials.