How to Treat Webworms in Grass and Tree

Webworm is used to describe several insects whose caterpillars use silk to join plant parts together to form protective nests.  Two common insects that create nests in grasses, fruit and woody ornamental trees are the eastern caterpillar and the fall webworm.  These insects should not to be confused with the forest tent caterpillar, whose name is a misnomer, because it does not make a tent.  Both eastern tent caterpillars and forest tent caterpillars are often mistaken for gypsy moth larvae because of their similar appearance.

Webworm is common insect that can cover grasses, leaves, clusters of leaves or leaves on whole branches, becoming several feet in diameter. They contain many hairy caterpillars that hatched from one egg mass. Some trees can have a high number of webs. Caterpillars grow to about 1 inch long, with black or reddish heads, pale yellow or greenish bodies marked with a broad mottled stripe containing two rows of black bumps down the back  and yellowish patterns on the sides. They are covered with tufts of long whitish hairs. Adult moths are mostly white with dark spots on the wings.

How to Treat Webworms in Grass and Tree

Webworm treatment options have to do with the life cycle of the critter. Webworms overwinter as pupae in cocoons found in the bark of the tree or amongst leaf litter. In the spring, adults emerge and deposit eggs, often creating large numbers of these caterpillar-laden webs in a single tree.

These caterpillars may go through as many as eleven growth stages (instars) before leaving the web to pupate and multiple generations occur per year. Here’s the tips on how to treat webworms in grass and tree:

  • Prune out webworm nests

The safest and most effective method on how to treat webworms in grass and tree is to prune the trees and grasses in the spring and spray with a lime-sulfur and dormant oil spray.

Fall webworms and forest tent caterpillars rarely reach large enough populations in ornamental trees to cause serious damage.  Typically, grasses and trees can recover from feeding damage.  However, nest and feeding damage can lower the aesthetic value of a tree.  In addition, repeated defoliation year after year may contribute to grass and tree decline.  On small grasses and trees, webworm nests can be removed or pruned out.  Simply scrape or prune the nest off onto the ground and crush to destroy the caterpillars.  Remove nests in the early morning or late afternoon because more caterpillars are located in nests at these times.  In larger grasses and trees, insecticide treatments may be necessary.  Treat small, young caterpillars while they are inside the nest in the morning or late afternoon.

  • Use of varieties of insecticides

Webworms infestations are more common than you might think and can be difficult to treat if you don’t know how.

The control of fall webworms also includes the more toxic varieties of insecticides, such as Sevin or Malathion. Sevin is a webworm treatment that kills the webworms once they are outside of the nest. Malathion works in much the same manner; however, it will leave a residue on the tree’s foliage. Orthene is also an option for fall webworm control.

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