A Significant Flight of Black Cutworm Moths Arrived in Franklin County

Again this year, Penn State Extension and the Department of Entomology are monitoring black cutworm populations with pheromone traps. As moths arrive, if we capture eight or more moths over the course of two nights (a "significant flight"), there is an elevated risk in that particular area of cutting damage by black cutworm caterpillars later in the spring.

So far this spring, we have only detected significant flights of black cutworm moths in Guilford Township near Chambersburg in Franklin County. Other locations across Pennsylvania have not yielded significant flights of moths, but we continue to trap for moths. The first significant flight of moths near Chambersburg occurred on 7 April, and that site has accumulated about 220 growing degree days since 7 April. Cutting damage in corn fields is predicted to occur about 300 degree-days following significant flights; therefore, near Chambersburg the time to scout for cutting damage should arrive around 20 May. Chambersburg also saw subsequent significant flights of black cutworm moths later in April, suggesting that part of the state has an elevated risk of cutworm damage even after 20 May.

This significant flight should not prompt you to add insecticides to any herbicide applications you will be doing soon, because applications of insecticides without knowing your local cutworm populations are unlikely to be effective or profitable. If you deploy insecticides this way and do not see damage, an equally plausible explanation is that caterpillar populations in your area were low.

When you scout your fields, note that black cutworm caterpillars can damage corn from first emergence up through V4 (damage to V5 is rare). Economic thresholds for black cutworm damage to corn are 2, 3, 5, and 7 caterpillar-cut plants per 100 seedling-, V2-, V3-, and V4-stage plants. In young plants, cutworm damage can appear as a series of symmetrical holes in the leaves (see photo). Remember that if cutting damage is found, rescue treatments are usually the most efficient and economical tactic for managing black cutworm. For more information, see the Penn State Extension fact sheet on black cutworm.