May 16, 2008

With the armyworm moth flight declining in the University of Kentucky Integrated Pest Management pheromone traps in Princeton and Lexington, small grain and pasture producers must now watch their fields and wait to see if armyworm problems develop.

In Lexington, the moth count for the week of May 2 through May 9 was down to 518. This is a large decrease from the previous week’s count of 1,011. Princeton’s count declined for the second straight week to 61.

“The data shows the moth flight peak has occurred, and there’s no doubt that we’ll see the numbers continue to drop,” said Doug Johnson, UK extension entomologist.

Moths are early indicators of the possible number of caterpillars that could begin to feed on Kentucky fields and crops. The moths lay eggs on the lower leaves of grass plants, and caterpillars hatch from them. If present in large enough numbers, armyworms can damage pastures, corn, hay and small grains.

Two reports of armyworm infestations have already surfaced in Carlisle and Henry counties. Johnson said in both cases, the worms were very small and on corn. But since the peak moth flight occurred during the week of May 2 for Lexington and the week of April 25 in Princeton, the largest numbers of armyworms could possibly appear within one to four weeks.

However, this is not a certainty. While the number of moths is an early indicator for the number of armyworms, several natural predators, parasitoids and diseases could destroy the armyworms and the eggs.

Farmers should scout their crops and pastures for armyworms during the upcoming weeks. Pasture producers need to scratch around on the ground for armyworms, as they may be very small and tend to hide during daylight. The tallest grass often will have the largest numbers of armyworms.

Johnson said, as they look for worms, pasture producers should be careful not to confuse armyworms with other insects, such as sawfly larvae, that may be on the ground. Sawfly larvae can often be confused as armyworms. Armyworms are a greenish-brownish color with a tan head with dark spider web like markings. They have three sets of legs near their head and four near their end. Sawfly larvae have green heads and a set of legs on each body segment.

No action may be necessary if producers find armyworms, but that depends on the number of armyworms and extent of the damage. While armyworms can damage pasture grass, they do no damage to the root system. Rain will help damaged grass recover. However, if the situation is extreme, an insecticide application may be necessary.

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