Numerous Reports of Black Cutworm Damage to Corn and Soybean Seedlings

Published: June 6, 2011

During the past 10 days many reports of black cutworm damage to seedling corn plants and soybean have been received. Larvae produced from late moth flights have reached the 4th instar or later stages of growth and are causing problems on seedling corn and soybean plants in fields scattered across the state. Black cutworm larvae occasionally cause damage to seedling soybean when their feeding activities result in high plant mortality. In most years, low populations of black cutworm larval in soybean go unnoticed as surviving plants often compensate for lost plants. However, moderate to heavy feeding by black cutworm larvae on soybeans seedlings may substantially reduce crop yields if high seedling mortality occurs. Although a good economic threshold for black cutworm feeding on soybean seedlings is lacking, 20% or more cutting of soybean seedlings has been used in past years. With the higher commodity prices for soybean, this economic threshold is probably too conservative. As commodity prices go higher, producers can afford to treat pest infestations at lower thresholds. With this in mind, an economic threshold of 10% or more cutting is a more reasonable economic threshold for black cutworm infestations in seedling soybean. Soybean producers are encouraged to monitor soybeans stands at least twice per week during the next month to make sure cutworm larvae are not reducing plant stands to unacceptable levels. Seed applied insecticide treatments on soybean should help reduce black cutworm larval numbers, but may not prevent economic damage in situations where larval feeding is severe. In corn, these seed treatments often control about 50% of black cutworm larvae under heavy infestations. They should work better in soybean where the treated seed is grouped closer together in the row. However, insecticide efficacy data on black cutworm in soybean is very limited for many of the new seed treatments. A list of rescue application insecticides for black cutworm control in soybean is as follows. Be sure to follow label directions concerning whether the insecticide selected for rescue or replant needs to be incorporated or simple broadcast over the soil surface.