University of Maryland Extension

Cankerworm

cankerworms

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.  Larvae finish feeding in late May or early June in the mid-Atlantic.

 
 Management

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.
 

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