Armyworms Spotted in Southwest Missouri Fescue Fields

Contact: Jill Scheidt, agronomy specialist
Tel: (417) 682-3579
E-mail: scheidtjk@missouri.edu

LAMAR, Mo. – Armyworms were seen in southwest Missouri wheat and fescue fields this week in numbers anywhere from 1 to 7 armyworms per square foot according to Jill Scheidt, agronomy specialist with the University of Missouri Extension in Barton County.

Threshold levels for armyworm in fescue are 4-5 per square foot and before 2-3 percent of heads are clipped.

Scheidt made the discovery while scouting area fields on May 29 to prepare this week’s MU Extension field scouting report.

A very small amount of armyworm feeding was seen in corn fields. Control of armyworm in field corn is justified if 25 percent or more of corn seedlings are significantly damaged through foliage feeding by larvae.

SCOUTING

To scout for armyworms, find a thick area in field or pasture, armyworm moths lay eggs in thick areas first, then beat the heads together and look for armyworms on the ground. “It is best to scout at dusk or early morning, while feeding is taking place,” said Scheidt.

The rate of development for armyworms is temperature related, so it may be hastened by warm weather or slowed down by cool weather. It typically takes two to three weeks from the time the moth lays the egg until they have hatched and grown through the early instars.

Instar is a rating, or size that describes the development or maturity of the larvae. Larvae at the 3rd through 5th instar are the most destructive.

Larvae have a greenish brown body, nearly hairless, with a thin stripe down the center and two orange stripes along each side. Armyworms are identified by four pro-legs at the middle of their body.

According to Wayne Bailey, MU State Entomologist, fescue fields need to be scouted first. “Armyworms typically show up in fescue fields two weeks before they are in wheat fields,” said Bailey.

CONTROLLING

A rate of three to four ounces per acre of Mustang Max is the recommended control for fescue fields with a zero day harvest interval for hay, forage and grazing.

“Armyworms should be treated as soon as threshold levels are seen; armyworms can clip 50 percent of the heads in a pasture in one night when at threshold levels. Larger armyworms cause more damage than full grown armyworms,” said Scheidt.

Prolonged wet weather can be hard on the armyworm larvae by creating conditions whereby a fungus knocks down the population. They prefer cool weather and do not like sun and heat.

“There is also a wasp that can parasitize and kill the armyworm. This is a natural predator, but do not assume this will occur. It is important to check for parasitism when determining threshold levels for spraying. Look for mummified bodies of armyworms clinging to the plant stalks or laying in the plant debris on the ground,” said Scheidt.

MORE INFORMATION

The weekly field scouting report is sponsored by University of Missouri Extension and Barton County Extension.

For more information on this scouting report, or to learn how you can receive it a week earlier by telephone, contact the MU Extension Center in Barton County at (417) 682-3579.

For more information about armyworms or to receive a copy of the Armyworms and their Controls guide go online to http://extension.missouri.edu/webster/webster/agric/armyworms-field.html