Corn Earworm

Corn earworm moths are most active during evening and night. They are about 0.75 inch long, rather robust, with a wing span of 1 to 1.5 inches, and adults range from olive green, to tan, to dark reddish brown in color. Egg laying occurs throughout the sweet corn growing season. The tiny, white eggs are laid singly on the foliage and fresh corn silk, which is the favorite site for egg deposition. After about a day, eggs develop a reddish brown ring in the top portion. Eggs are spherical with 12 or more ridges radiating from the top. Young larvae are greenish with black heads and conspicuous black hairs on the body. Fully developed worms are about 1.5 inches long and range in color from pale green or pinkish to brown.

The corn earworm may be present throughout the season but is most abundant during August and September. Larvae feed on leaves, tassels, the whorl, and within ears, but the ears are the preferred sites for corn earworm attack. Ear damage is characterized by extensive excrement at the ear tip. Young larvae feed on corn silks, clipping them off. Shortly thereafter, they feed their way into the ear where they remain, feeding in the tip area until they exit to pupate in the soil.

Corn earworm is primarily a problem in sweet corn where treatments should be timed to coincide with egg hatch.

Many predators and parasites attack corn earworm eggs, including several species of Trichogramma. Most parasitized eggs turn black, but there may be a lag period before they do so. General predators such as lacewings, minute pirate bugs, and damsel bugs feed on corn earworm eggs and small larvae.

In sweet corn, very early plantings require fewer treatments than late-season corn because earworm population densities increase as the season progresses.

Biological and cultural controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on an organically grown crop.

Insecticidal control of corn earworm is difficult and depends on proper timing and thorough coverage. Begin sampling soon after corn emergence but pay particular attention to corn that is silking in late summer/early fall. The presence of large numbers of eggs on fresh corn silks indicates the potential for damaging populations. Eggs hatch in 5 to 7 days following oviposition. Once larvae enter the corn ears, control with insecticides is difficult. Direct insecticidal control towards young larvae that are feeding on the exposed ear tips. Treatments are usually not needed on field or silage corn. In sweet corn, where tolerance for worm damage is low, timing of insecticide treatments is critical: begin treatments during silking stage, at the start of egg hatch. Apply additional treatments if they are necessary.