The fall webworm, Hyphantria cunea (Drury)(Lepidoptera: Erebidae) (Fig. 1) is a polyphagous caterpillar pest of ornamentals and trees in Georgia. It is known to feed on more than 600 species of plants including row crops, herbaceous plants, shrubs, fruit and ornamental trees in orchards, nurseries and landscapes. Fall webworm larvae construct a silk web nesting to facilitate feeding, to escape the attack of natural enemies, and for heat retention. The webbing is unsightly, and feeding on foliage inside the nest leads to extensive defoliation. The fall webworm can quickly reduce aesthetic appeal of landscape trees and shrubs (Fig. 2), and severe infestation can cause considerable damage to trees.
Biology of the fall webworm
The fall webworm is active during the summer and the early fall. The white, hairy female (Fig. 1) moth deposits approximately 600 eggs on the underside of leaves in masses covered with white hairs from the female body (Fig. 3). The eggs hatch within a week. The red- or black-headed larva is covered with fine hair (Fig. 4). Almost immediately, these larvae begin working together to construct their silken web over a branch tip and begin to feed. Initially, they skeletonize the leaves inside the web (Figs. 5 and 6) but as the larvae develop, the webbing expands and covers more foliage on the tree branch. Larvae feed for up to six weeks until pupation. Mature caterpillars leave the web to pupate under bark crevices, soil, or under stones. The pupal period may range from 12-80 days, depending on environmental conditions, followed by adult moth emergence. The fall webworm overwinters as pupa and can have multiple generations in a year.
Management of fall webworm
Regular inspection of trees and shrubs starting mid-summer will help detect infestations. Traps containing sex pheromones were developed to determine early flights. As part of cultural control, pruning infested branches will reduce extensive webbing. However, intensive pruning is not recommended as it can reduce productivity of fruit trees. Biological control plays a critical role in reducing fall webworm populations. Many beneficial arthropods, including spiders, insect predators, and parasitoids, are found to be associated with the fall webworm. Vertebrate predators like birds and lizards will also feed on the caterpillars given the chance. Disrupting the protective webbing usually leads to death of all or most of the caterpillars inside, so any nests within reach of a long pole can be torn open as a control measure. The microbial insecticide, Bacillus thuringiensis is commercially available and can be used to manage fall webworm. Many synthetic insecticides are available, but spraying insecticides on a tree of any size is problematic and should only be attempted by trained professionals. Contact your county Extension office for insecticide recommendations. If insecticides are used, always read and follow label instructions. It is the law.
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