University of Maryland Extension



Key Points

  • There are two species of cankerworms that can be a problem on shade trees: spring cankerworm (Paleacrita vernata) and fall cankerworm (Alsophila pometaria). 
  • They attack many forest and shade trees but prefer apple, elm, oak, hickory, linden, birch, beech, and maple. 
  • Caterpillars of both species have green and brown to gray forms and may be found feeding together in the spring. 
  • To distinguish between the two species the spring cankerworm has 2 pairs of prolegs while the fall cankerworm has a small 3rd pair. 
  • Leaf damage initially appears as shot holes. 
  • In heavy infestations, the leaves appear shredded and trees may be defoliated. 
  • Caterpillars finish feeding in late May or early June in the mid-Atlantic.


  • Monitor trees to determine if control is necessary.
  • Bacillus thuringiensis (or Btcan be used in the spring when leaves of infested trees are 50% expanded. 
  • A registered chemical insecticide will be necessary when heavy infestations are found after mid-May.

Rev. 2020

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