Armyworm—Sheer Numbers Are the Source of
This Worm's Damage

The armyworm is a noctuid moth larvae that travels in groups, destroying grass and grain crops. Also known as Pseudaletia unipuncta, a moth. Mainly found east of the Rocky Mountains.

Armyworm Description

The young larvae are pale green. Older larvae become pale green brown to a black.

They move arching the body into a loop while they crawl.

Most will reach a length of 2 inches (5 cm).

The western yellowstriped armyworm is black color with orange and yellow stripes on the sides of the body.

The moth is grayish brown with a white spot on each forewing.

Damage Caused

• Larvae cause damage by eating leaves. Entire leaves may be consumed, or the damage may consist of notches chewed out of the leaves, giving them a tattered look.
• Damage starts when larvae hatch from eggs laid in the cereal crop.
• These worms move in hordes, traveling at night and devouring grasses, young grains, and some leguminous crops.
• There are usually two generations in a year, the larvae hatching from eggs in late spring and again in late summer.
• The armyworms are especially damaging in the second generation, which occurs when corn and wheat are maturing.

Biological Control

• The worms are attacked by a parasitic wasp, Hyposoter species.

  Parasitized worms can be identified by pulling the larvae apart and looking for the green parasite larvae that pop out.

  Hyposoter is usually not active in early spring when cereals may be attacked by these worms but it should be looked for.

• Virus diseases of the armyworm may also be important natural control agents. Diseased caterpillars first appear yellowish and limp, and after death hang from plants as shapeless, dark tubes from which the disintegrated body contents ooze.

Organically Acceptable Methods

• Bacillus thuringiensis in biological and cultural controls sprays.

Cultural Control

• To stop larvae from moving into a cereal crop from an adjacent crop, plow a deep, wide ditch between the two fields and keep it filled with water until the migration stops.
• Dig deep holes as traps.

If this page was valuable for you, please share your new knowledge. Click Like...