Armyworm moths set to invade crops

PRINCETON, Ky. — In recent days, the number of armyworm moths captured in the University of Kentucky-Integrated Pest Management pheromone trap system has set record levels. This could set up the potential for large enough numbers of armyworms to emerge in the weeks ahead to cause crop damage.

For the week ending April 25, capture of moths in the Princeton trap increased to 600 moths per trap-week, said Doug Johnson, University of Kentucky Extension entomologist.

This is a larger peak than in any first-generation flight since the group has been keeping records, and a substantially larger number than in the outbreak years of 2001, and 2006.

Don’t overreact

Johnson said the high counts are no reason to overreact.

“This is an early warning, not a prediction of catastrophe,” he said. “I cannot tell you if the moth flight will result in a large population of caterpillars. There are many other factors, particularly disease, predation and parasitism that impact how well the eggs and caterpillars will survive. Nevertheless, I do think that we are at an increased risk of economically important infestations compared to most years. Certainly you should be scouting your grass crops.”

Armyworms, or true armyworms as this species is commonly called, occasionally occur in large enough numbers in the springtime to cause damage to pastures, hay, corn and small grains. Cool, wet spring weather usually favors armyworm development.

A degree-day model can be used to estimate when the caterpillars resulting from these moths might appear.

Peak activity

Calculations April 28, using the captures for the week of April 19-25, to represent the peak flight for the first generation this year, predict farmers can expect to see peak caterpillar activity for the first generation to occur around May 20-25 in Kentucky.

Additionally, these dates are based on the Princeton and Lexington locations only. Other areas that are warmer or cooler may have populations that appear earlier or later. Some fields may need to be treated to control the insect. Scouting is the key to determining if a field will need to be treated.