|Sorghum Webworm: Nola sorghiella Riley|
|Description and Biology: The sorghum webworm is an occasional pest found in panicles of late-planted sorghum. This insect pest occurs primarily in humid areas. The adult is a small, white moth with a wing span of about 13 mm. Moths are active at night, laying about 100 eggs singly but rather securely fastened to flowering parts or kernels of sorghum. Eggs (0.5 mm in diameter and 0.25 mm in height) are round to broadly oval in outline and flattened. They are white at first but turn deep yellow to brown before hatching in three to four days. Larvae are flattened, yellowish or greenish brown, and marked with four longitudinal reddish to black dorsal stripes. Larvae are 13 mm long when mature and covered with spines and hair. The larval stage lasts 13 days. The pupa, within a cocoon, is reddish brown, slender, and sub-cylindrical. The pupal stage lasts six days, and adults live about five days. A generation requires one month. There may be as many as six generations a year. Sorghum webworms diapause as larvae, hidden on the host plant.|
|Symptoms and Damage: Large numbers of sorghum webworms may be found in panicles, especially of late-planted sorghum. Young larvae feed on developing flower parts. Older larvae gnaw circular holes in and feed on the starchy contents of maturing kernels, which usually are only partly consumed. Each larva may consume more than 12 kernels in 24 hours. Larvae do not spin webs (as the name might imply) over the panicle but, when disturbed, young larvae often suspend themselves by spinning a silken thread.|
Monitoring: Panicles should be inspected when they are beginning to flower and five-day intervals until kernels are in the hard-dough stage. To examine panicles for sorghum webworms, shake panicles vigorously into a 19-liter bucket. Even small larvae can be seen and easily counted in the bucket. At least 30 plants from a field should be inspected to ensure reasonable reliability of sample estimates. Fields larger than 32 hectares should be divided for sampling into areas no larger than 32 hectares.
Management: Cultural controls include plowing under crop residues to destroy overwintering larvae, planting early, and using sorghum with open (loose) panicles. Most insecticides can be used to control small webworms. Insecticide applications are economically justified when there is an average of five or more small larvae per panicle.