Sod Webworms
Crambus spp., Pyralidae, LEPIDOPTERA


Description (several species)

Adult - These small, white to brownish-gray moths are 13 to 19 mm long and have a pointed "snout" (labial palps). At rest, wings are wrapped around the body. When disturbed, the moths fly in an erratic manner for a short distance.

Egg - The tiny eggs are oblong and pale.

Larva - The larvae vary from pinkish-white to yellowish to light brown. When fully grown they are 16 to 19 mm long and have thick bodies, coarse hairs, and paired dorsal spots and lateral spots on each segment.

Pupa - The reddish-brown pupae are about 13 mm long.


BIOLOGY

Distribution - Many species of webworms, all native to America, periodically infest corn throughout the United States and Canada. Damage by these pests, however, is most prevalent in a central band of states from North Carolina and Massachusetts westward into Iowa.

Host Plants - Webworms primarily infest the roots of many grasses causing problems in lawns, golf courses, and pastures. They are usually a threat to field crops such as corn and tobacco only when these crops follow sod. Some species overwinter near the roots of weeds such as stickweed, plantain, and fleabane.

Damage - Webworms attack the roots of seedling corn plants. The larvae feed on the stalk at or below the soil surface. As the leaves emerge, they are ragged, distorted, and almost perpendicular to the stem. When webworm damage is heavy, the whole plant may be curled or twisted and the growing point killed. Careful examination around the base of an infested plant will reveal scarred or damaged tissue on one side of the stem plus at least one hole extending into the center of the plant. Fine silken strands intermingled with bits of plant material or soil pellet cocoons are usually present.

Life History - Webworms overwinter within silk-lined tubes in the soil. Early in the spring, they emerge and feed at night on roots of grasses, weeds, and cultivated plants. In southern states, larvae have usually completed feeding by June 1, whereas in Ohio and Indiana feeding may continue until July 1. When mature, the larvae pupate within a silk-lined cocoon made up of soil particles and leaf blades interwoven with silk. Moths emerge 10 days to 2 weeks later, push their way to the soil surface, and mate soon afterwards. For the few days that they live, female moths fly at dusk and drop eggs over grassy areas. Eggs hatch in approximately 7 days. Depending on geographic location and the particular webworm species, these pests complete one to three generations each year.


CONTROL

Cultural methods are very important in controlling webworms in corn. If possible, avoid planting corn in fields which in pasture or sod the year before. Where this is impossible, plow the grassy field under in mid-summer or early fall the year before planting corn. This cultivation will help deter egg deposition and destroy many overwintering larvae. The next year, plant high quality, certified seed at the proper time, fertilize the crop well to give it a good start, and use a granular, labeled, soil insecticide. Varieties particularly susceptible to the European corn borer are also easily damaged by webworms.

For further control information, consult the current North Carolina Agricultural Chemicals Manual.