For the past 3 weeks, corn earworm moth counts in pheromone traps have been increasing in Central Kentucky. Corn earworm can be a serious pest of a number of crops, including, but not limited to, sweet corn, hemp, tomatoes (a.k.a. tomato fruitworm), field corn, and soybeans (a.k.a. soybean podworm). In years following a mild winter, high levels of corn earworm are able to survive in Kentucky soils as immatures, resulting in high early-season populations. However, this past winter Kentucky had more of an average year with some soil freezing. Judging by trap counts, populations have rebounded this summer and producers will need to monitor and manage corn earworm on susceptible crops.
Sweet Corn Risk
The two crops that are at particular risk later this summer are sweet corn and hemp. With early planted sweet corn, there is a much lower risk of corn earworm attack. I consider early planting to be before the end of May. However, June-planted sweet corn is at a much higher risk of corn earworm attack. The key period of attack is during silking and when the silks are fresh. The fresh silks produce volatile chemicals that attract the female moths. After the silks dry, plants are not as attractive for egg laying.
Some producers use Bt-sweet corn to manage corn earworm, but research in Lexington has shown that Bt-sweet corn should be part of a corn earworm management program and needs to be supplemented with insecticides to avoid damage.
Monitoring Sweet Corn with Pheromone Traps
Pheromone traps are used to capture corn earworm male moths to give growers an idea of population levels in the area and the relative threat to sweet corn. During silking, if up to 10 moths are captured per week, growers should spray every 5 days until the silks dry. If up to 350 moths are captured per week, treat every 4 days, and when this count is over 350 moths, treat every 3 days. Based on the number of moths that have been captured in Central Kentucky over the past few weeks, growers would be spraying sweet corn every 4 days during silking.
Field Corn Risk
In terms of field corn, the risk of corn earworm losses in less clear, particularly in Central Kentucky. This is largely due to typical planting dates with field corn and possible compensation of undamaged portions of the ear when the tip is damaged. A multi-year study in Lexington conducted from 2012 to 2014 failed to show yield loss to corn earworm even with later plantings.
By Ric Bessin, Entomology Extension Specialist