Thursday, July 31, 2008

Fall webworm

Looked at walnut trees lately? The one’s I’m observing have large white webs at the ends of their branches. This is a common sign of an insect called fall web worm that begins feeding about this time of year. By late summer these webby nests will engulf large portion of the limbs. It’s unsightly but not a big deal because they feed so late in the season that the trees have already stored lots of energy to sustain themselves. So, the webbing is ugly but not cause for alarm. I see them in wild cherry trees, too. Sassafras, persimmon, sweetgum and about 200 other deciduous tree species are host plants for this insect.
Inside the nests you’ll find pale yellow, hairy caterpillars with black dots on the back. When disturbed they may begin to jerk around rhythmically in a defensive posture. Pretty cool. Many parasites and predators keep the population in check… in the long run.
If you can’t stand the look of them, you can simply cut of the offending branch. But most of the time it’s way up in the canopy of the tree, beyond reach. Insecticides will kill them but pruning is a more selective, reasonable choice if you have to do something. And remember that this is mostly a cosmetic problem, not a tree health problem.

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