Thursday, September 16, 2010

Fall Webworm Outbreak

Many of you have probably noticed trees covered with the silk tent homes of the fall webworm Hyphantria cunea this summer.  The webworm caterpillar favors foliage from walnut, hickory, black cherry, elm and fruit trees.  Adult wedworm moths lay eggs on leaves then upon hatching the larvae rapidly consume the soft tissue of the leaf while covering it with a silk surface.  Entire branches of trees can be consumed by the silk tents and in some cases whole trees can be defoliated.  Luckily, most trees are healthy enough to withstand the webworm invasion even in complete defoliation. 
Webworms infest a black cherry Prunus serotina branch.  The
caterpillars are small (less than an inch) in size and are easily
concealed by the silk structure which can contain dozens of
individuals.  A tree with several tent colonies can easily be
defoliated in a matter of days.

Webworm tents in the top of a black walnut tree.  Interestingly
I've read that stinkbugs are efficient predators of webworm
caterpillars as well as parasitic wasps.  However, in a year with an
extreme outbreak, natural predators are overwhelmed and quickly
become engorged with the worms reducing their effectiveness.

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