University of Maryland Extension

Fall Webworm - Trees

fall webworms in webbing
Fall webworms

Key Points

  • 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. 

Damage

fall webworm

  • 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.
  • Bt (Bacillus thuringiensis, var. Kurstaki), horticultural oil, or insecticidal soap is recommended to control young larvae in large infestations to protect beneficial insects.
  • There are 75 species of predators and parasites that normally keep this pest below damaging levels. 
  • Never try to burn them out!!

fall webworm in tree

Rev. 2020

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