The webworm, Hyphantria cunea (Drury), is a common pest of trees. Webworms are caterpillars that feed protected by webs; these caterpillars primarily feed on leaves. They vary in size from 1/2 to nearly 1 1/2 inches in length. Full grown larvae are about an inch long and are very hairy, with pale yellow stripes along the sides.
Webworms are known for the large, unsightly webs they produce. Some trees appear to be wrapped almost entirely with webs. Webworms attack more than 120 varieties of fruit, shade, and woodland trees. Among their favorites are apple, peach, pecan, black walnut, birch, elm, hickory, poplar, white oak and willows. Occasionally they attack roses and other shrubs.
Initially the web covers a few leaves on a branch. As larvae grow, entire branches may be infested. Webs often are 2-3 feet long. The larvae eat entire leaves except for the midrib and veins. Although the webs are unsightly, they usually do little serious damage to plants because defoliation occurs in late summer when deciduous trees and shrubs are going dormant. Webworms have many natural enemies that ordinarily keep the numbers down. But every few years the numbers increase and trees become heavily infested. Heavy infestations are rarely fatal, but if they occur repeatedly over several years they can stress trees and make them more susceptible to drought, disease or other insect pests which can be fatal.
These worms overwinter as pupae in cocoons under trash on the ground or under loose
bark. White moths emerge from May to August. Since adults emerge over several weeks, not all webs start at the same time. White eggs are laid in masses on the undersides of leaves.
As soon as they hatch, larvae begin to spin webs over the foliage and feed on the enclosed leaves. The web grows as larvae grow and eat foliage. Larvae remain clustered, usually not crawling away from the web until ready to pupate.
For small trees, webworm nests can be cut out and destroyed. A common practice -- burning nests in the tree -- isn't recommended. Several serious fires have been started by people
doing this. Spot treatment with chemical pesticides is effective when applied in June as larvae start to make webs. Where infestations are severe, spray the entire tree to avoid having to repeat the treatments. For control recommendations and treatment, call National Pest Mobiles at 214-341-1498.
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