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Vol. 17, No. 7
Article 5 of 9
April 27, 2007
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First Intensive Captures of Black Cutworm Moths By Wayne Bailey The first intensive capture of BCW moths in pheromone-baited traps occurred during mid-April. Intensive captures of moths indicate heavy moth activity, which may result in problems with black cutworm larvae in field corn. Intensive moth capture date along with meteorological data (30-year average) are used in the Missouri Black Cutworm Predictive Model to calculate a 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, the rate of black cutworm growth and development will be increased by as much as one week. If conditions are cooler than normal, 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 of first cutting. 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. For more information on the black cutworm predictive model and the counties currently monitoring for black cutworm, please visit our Website at: http://ipm.missouri.edu/pestmonitoring/blackcutworm/index.htm. Listed below are the trap locations with intensive captures (as of 4/22/07) and predicted dates of first cutting of field corn by black cutworm larvae:
Please be aware that intensive captures in pheromone traps only indicate a need for scouting fields. Intensive captures DO NOT indicate treatment is necessary. 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 spring from more southern states to mate and lay eggs on grasses, low growing winter annual weeds (henbit, chickweed, curly dock, others), in winter cover crops or soybean residues, and sometimes even on bare soil. 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 three- five percent cutting above ground and two-four percent cutting below ground. Most feeding damage typically occurs within seven to ten 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. 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 nonchemical option. This method depends on larvae mortality caused by exposure to harsh conditions and limited food. Seed treatments are another option which provide about 50 percent control of the insect in Missouri insecticide evaluations. In most years this rate of control may be suffi cient to keep larval numbers below economic threshold levels. In years with high black cutworm larval numbers, economic damage may occur with this method. Producers can also apply an insecticide prior to or at the time of planting. Several insecticides are labeled for this use and are generally effective for black cutworm larval control. A rescue application of insecticide is also effective in controlling this pest. This insecticide application is applied when scouting of the crop finds damage to the crop has reach or exceeded the economic threshold levels based on the quantity and type of cutting. 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.
Wayne Bailey |
