Corn earworm appearing in state

COLUMBIA, Mo. – Many late-planted and double-crop soybean fields in Missouri are at risk of damage from corn earworm, also known as soybean podworm, said University of Missouri Extension entomologist Wayne Bailey. Scout fields now because conditions are right for the development of economic infestations, he said.

“Corn earworm actually has more potential to reduce soybean yield than corn yield,” Bailey said. Corn earworm can reduce corn yields by feeding on kernels at the ear tip. It damages soybean by feeding on foliage and pods.

Most damage occurs to pods and seeds. This can result in delayed seed production and lower yields.

Small larvae feed on soybean foliage first. They can chew through pods to eat developing beans or cut pods from the plants. In very high numbers, larvae can eat pods that have dropped to the ground. This can cause up to 100 percent yield reduction of soybean, Bailey said.

Double-crop soybean fields throughout the state, especially in southern Missouri, are most vulnerable to podworm damage.

Check soybean fields several times weekly for foliage feeding, pod damage and presence of soybean podworm larvae. The best scouting methods for this pest are direct observation, or use of a shake cloth or sweep net, Bailey said.

There is a narrow window of time for treatment. “Larval infestations from earlier moth flights of soybean podworm can do a lot of damage,” he said.

Soybean podworm/corn earworm also can reduce sweet corn and field corn yields and damage cotton and sorghum. There are two to three generations per year in Missouri. This insect pest has many names related to the crops on which it feeds.

Soybean podworm do not present an economic threat to Missouri soybean in most years. Podworm problems could be greater this year because of more late-planted soybean acres due to spring precipitation. Another factor in 2014 is the lack of green cloverworm. Its larvae serve as an early-season host of a beneficial fungus responsible for most soybean podworm mortality later in the season.

Corn earworm remains a problem for Missouri corn producers as well. MU Extension agronomy specialist Jill Scheidt in Barton County said last week that she scouted a cornfield and found five earworms for every 10 stalks.

Once the worm has gotten into the corn ear, rescue treatments are often economically impractical and difficult, Bailey said.

The best option to prevent earworm in corn is to plant hybrid varieties containing a Bt gene for control of this pest, he said.

Earworms keep their own numbers down in individual corn ears as large worms eat smaller ones. Generally, there will be from one to three worms per ear tip.

Bailey said yield loss for corn varies by study. Estimates are as high as 8 percent, but 2 percent or less is probably more realistic, he said.

For more information, see the MU guide “Corn Earworm in Missouri” (G7110) at http://extension.missouri.edu/p/G7110, or go to the MU Integrated Pest Management website at http://ipm.missouri.edu.