Shade Trees: Leaves

Fall Webworm

Fall webworm (Hyphantria cunea) caterpillars may feed on more than 100 species of deciduous forest and shade trees. Preferred hosts include mulberry, walnut, hickory, elm, sweetgum, poplar, willow, oak, linden, ash, apple, and other fruit trees. The adult moths are about 3/4 inch long. The wings are all white or white with black spots. Mature larvae are about 1 inch long and may occur in two color forms: those with black heads are yellowish-white, and those with red heads are brown. Both color forms have paired black tubercles running down the back. They are covered with long, silky gray hairs.

The caterpillars produce a web of fine silk over terminal branches. They only feed inside the web, which they enlarge as they grow. Look on the south side of tree crowns for the first sign of webbing. The webs may become messy, but the caterpillars rarely consume enough terminal growth to affect the tree. The first generation begins in May and is usually small. The second-generation caterpillars are present from August through October. The dry webs hang on terminals into the winter.

Management: Prune out webbed terminals as they are detected. Pole pruners are useful for removing tents in trees. B.t. (Bacillus thuringiensis, var. Kurstaki), horticultural oil, or insecticidal soap is recommended to control young larvae in large infestations and protect beneficials. There are 75 species of predators and parasites that normally keep this pest below damaging levels.

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Mature larvae are about 1 inch long and may occur in two color forms: those with black heads are yellowish-white, and those with red heads are brown.

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