Posted 25 June 2007. PMN Crop News.
Time to Be on Lookout for Armyworm Larvae
University of Nebraska-Lincoln. casnr.unl.edu
Lincoln, Nebraska (June 19, 2007)--Armyworm moths are on the increase, and farmers should be on the lookout for developing caterpillar populations, University of Nebraska-Lincoln entomologists say.
"If you have been outside near your porch light the last week or so, you may have noticed a great number of moths flying around," said Tom Hunt, entomologist at the Haskell Agricultural Laboratory near Concord, Nebraska. "Many of these are simply a nuisance, but one, the armyworm moth, may have implications for Nebraska farmers."
UNL light traps at Hastings, Clay Center and Concord have been capturing increasing numbers of armyworm moths.
Armyworm moths migrate from the south and lay eggs on grasses, often in pastures, field edges, or on grassy weeds in cornfields. After eating the grass, or after the grass is killed by an herbicide, the larvae move onto the corn to feed. They feed at night, usually on the leaf margins, but can consume the entire leaf except for the tough midrib when populations are high, Hunt said. Armyworms often start feeding on the lower leaves and work their way up. The armyworm larvae also can injure wheat or other small grains.
Armyworm larvae are smooth with two orange stripes along each side and two dark stripes on the back. A distinguishing characteristic is a yellow-brown head with a brown netlike pattern of dark lines.
Cornfields with grassy weeds should be scouted regularly, particularly after the weeds begin to die following an herbicide application, Hunt said. Corn plants can tolerate quite a bit of early season defoliation, so farmers should not treat the field with an insecticide simply because they see some armyworm injury.
Hunt suggested treatment when more than 50 percent of the plants have armyworm injury and when the larvae are numerous and less than 1.25 inches long. Larger larvae are nearly done feeding, so little additional injury is caused by them.
Updated information on Nebraska light trap insect capture, armyworm management, and insecticide choice can be found at www.entomology.unl.edu. Information also is available in the NebGuide, Insects That Feed on Corn Ears.