Armyworm Moth Flight Takes a Down Turn!

Doug Johnson, Extension Entomologist

The most recent capture number for armyworm moths in the UK-REC trap shows a decided decrease, down to 87 moths/trap-week. This is an overall good sign that no large population is in the offing. This does NOT mean that any specific field will not have a problem population, only that there is unlikely to be a widespread large problem. Fields should still be scouted.

To have a quick look, check field edges and especially where wheat may be lodged. Armyworm caterpillars do not like bright sunlight and will tend to be in higher numbers in low light situations like lodged plants. They will also hide under plant debris. It is also a good idea to scout early in the morning or late in the evening, and/or during overcast periods. With just a little observation, one should be able to avoid any economic loss. In general, one only has to protect the flag and f1 leaves in small grains. Lowers leaves, especially those deep in the canopy, contribute little to yield.

Fig. 1. Armyworm caterpillar

Armyworms tend to feed at night and damage small grains and corn by stripping the leaves. They feed from the margin in toward the mid rib. In small grains, whole leaves will be consumed, but in corn they tend to leave the center portion of the leaf. Also in corn, they may feed in the whorl and destroy the bud.

Caterpillars will begin to appear in low numbers as offspring of the earliest moths emerge. There will be small numbers at first, then the population will increase in size. Larvae are greenish brown with a narrow mid-dorsal stripe and two orange stripes along each side. The yellowish head is honeycombed with dark lines. Armyworms tend to do best in cool wet conditions. Warm spring weather favors parasites and disease development in the caterpillars.

The economic threshold for small grains is 16, ½-3/4” larvae per four-feet². In corn, the guidelines are 35% or more of plants infested AND 50% or more defoliation and larvae averaging ½” – ¾” in length.

Armyworms are not hard to control. Losses are usually associated with lack of detection. Insecticides for use against this pest may be found on line at:

http://pest.ca.uky.edu/EXT/Recs/ENT47-SmallGrain.pdf for field corn and

http://pest.ca.uky.edu/EXT/Recs/ENT16-Field%20corn.pdf  for small grains, or at your local county extension office.