“Young corn seedlings and plants can be at risk. The economic threshold for spraying this pest is when 25 percent or more of the plants are being damaged.

"If the outbreak elevates to a high level, armyworms can consume a large amount of foliage and stunt the crop. Check the seedlings and the whorls for leaf feeding,” said Schnakenberg.

Fescue seed and wheat producers should also be watching closely because large numbers of armyworms may not only defoliate the plant but also clip heads as well.

“Treatment is justified in pastures and wheat fields when there are an average of four or more half-grown or larger larvae per square foot and before more than two or three percent of the heads are cut,” said Schnakenberg.

Dusk or dawn is the best time to be scouting for true armyworms because the young larvae are typically night feeders. During the heat of the day they will be under plant debris on the ground. As the larvae get bigger they will do an increased amount of day-time feeding.

The larvae have a greenish-brown body, nearly hairless, with two orange stripes along each side. The head is brown with honeycomb markings.

According to Schnakenberg, once the moths move into an area, they lay their eggs and it may take two to three weeks for the young larvae to start doing damage. It only takes the larvae five to seven days to grow from one-half inch to 1.5 inches in length.

“After they reach about 1.5 inches they begin to pupate, going into the ground and making a cocoon. This first generation of true armyworms is generally the most damaging,” said Schnakenberg.


Producers can monitor insect activity through the Missouri Pest Monitoring Network, where they can also sign up for a free email notification if an insect alert occurs around the state.

For information on sprays for true armyworms, visit the Greene County Extension websiteFG

—From University of Missouri Extension news release