First Intensive Captures of Black Cutworm Moths

Published: April 13, 2011

The first intensive capture of BCW moths in pheromone baited traps occurred during late March in 2011. Intensive captures of migrating moths indicate heavy moth activity which may result in problems with black cutworm larvae produced in field corn. Both the date of intensive moth capture along with meteorological data (30-year average) are used in the Missouri Black Cutworm Predictive Model to calculate a predicted date for first occurrence of cutting damage by 4th instar black cutworm larvae. These predicted dates of first cutting are based on meteorological averages in the area of the trap and may vary depending on weather conditions and temperatures from the time the eggs are laid through development of larvae. For instance, if temperatures are warmer than average, then the rate of black cutworm growth and development to 4th instar will be increased by as much as one week. If conditions are cooler than normal, then development of this pest will be slowed and cutting will occur later than predicted. To account for some of this variation in local environmental conditions, the predicted date is updated daily using data from a weather station near the trap site. Intensive moth captures do not always result in economic infestations of black cutworm, but do predict a date for potential first cutting by larvae.

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 minor leaf feeding on corn plants. More than one intensive capture of moths may occur at a trap site. Larvae produced from moths of each intensive capture have the potential to damage corn plants. In instances where intensive captures occur at a trap site early in the season and then again a couple of weeks later may result in two distinct larval populations and possibly two economic infestations in the same field. Because multiple black cutworm infestations may occur in a field, producers should continue to scout fields until the corn plants grow through the 5th leaf stage of development. For more information on the black cutworm predictive model and the counties currently monitoring for black cutworm, please visit our Website at: http://ppp.missouri.edu/pestmonitoring/bcw/index.cfm

Listed below are the trap locations with intensive captures (as of 4/11/11) and predicted dates of first cutting of field corn by black cutworm larvae:

Northwest Region

• Holt County (Forbes): Intensive capture date, 04/06/2011. Predicted first cutting, 05/06/2011
• Buchanan County (St. Joseph): Intensive capture date, 04/06/2011. Predicted first cutting 05/06/2011.

West Central Region

• Vernon County (Nevada): Intensive capture date, 03/27/2011. Predicted first cutting, 04/06/2007

North East Region

• Knox County (Novelty): Intensive capture date, 4/18/2007. Predicted first cutting, 4/28/2011. Intensive capture date, 03/31/2011. Predicted first cutting 4/28/2011. Intensive capture date, 04/06/2011. Predicted first cutting 05/02/2011.

East Central Region

• Franklin County (Union): Intensive capture date, 04/05/2011. Predicted first cutting, 04/30/2011.

As roughly illustrated by 2011 early trap data, black cutworm moth captures to this point in the season, follow a pattern beginning around Kansas City, move along the I-70 corridor to the St. Louis area, and then travel northward into northeast Missouri counties. Although this moth capture pattern may vary from year to year depending wind patterns, it is a pattern often observed in Missouri for black cutworm moth movement.

Please be aware that intensive captures in pheromone traps only indicate a need for scouting fields. Intensive captures DO NOT indicate treatment is necessary.

Life Cycle/Biology
The black cutworm, Agrotis ipsilon (Hufnagel), can be a severe pest of field corn and other crops in Missouri. Moths migrate into the state each srping from more southern states to mate and lay eggs on grasses, in winter cover crops or soybean residues, some bare soil, and low growing winter annual weeds, i.e., henbit, chickweed, curly dock, etc. These activities occur during early spring generally prior to the planting of corn. When this vegetation is killed and corn planted, surviving larvae readily attack emerging corn seedlings. Each female moth is capable of laying about 1,300 eggs either singularly or in small clumps. Larvae grow rapidly and reach the larval stage (4th instar) capable of cutting corn plants in 2-3 weeks. Corn plants may be cut near the soil surface or below ground. The economic threshold for black cutworm larvae attacking field corn seedlings is 4-6% cutting above ground and 2-3% cutting below ground. Most feeding damage typically occurs within 7-10 days following plant emergence.

Black cutworm larvae vary in color from light gray to dark black. The skin is rough or granulated and often appears greasy in texture. The sides and top of larvae are generally a solid gray or black color with an indistinct pale stripe running the length of the back. Black cutworm larvae can be confused with the dingy cutworm, although in Missouri dingy cutworm larvae often occur in the field at least two weeks prior to occurrence of black cutworm larvae. Additionally, dingy cutworms are typically foliage feeders during their larval stages, whereas, the black cutworm foliage feeds when small and cuts corn plants when it reaches the 4th instar stage of growth. There are a total of six instars for the black cutworm with several generations produced each year. However, larvae from the first generation are generally responsible for attacking field corn.

Management Options
Several management options are available for black cutworm in field corn. The destruction of winter annual weeds and vegetation at least two weeks prior to planting corn is a good non-chemical control option. This method depends on high larvae mortality caused by exposure to harsh field conditions and limited food supply. The addition of an insecticide with or without vegetation management provides good larval control prior to and at planting. Seed treatments are an option that historically provided about 50% control of black cutworm larvae in Missouri insecticide evaluations. In most years this rate of control may be sufficient to keep larval numbers below economic threshold levels. The recent addition of transgenic insecticide traits in some corn hybrids provide black cutworm larval control approaching 100% and are growing in popularity. A rescue application of insecticide is also effective in controlling this pest. A rescue insecticide is applied when scouting of the crop finds damage has reached or exceeded the economic threshold levels based on the quantity and type of cutting, the presence of half-grown or smaller larvae, and the stage of plant growth is at or less than the 5-leaf stage for corn.. Regardless of the method used, producers are encouraged to scout field corn at least twice per week from the time of emergence through the 5th leaf stage of plant development. Most early season insect corn pests can be found and successfully managed with good scouting practices and the use of an effective integrated pest management program.