Question
I have looked on this site and at first thought I had Bark Lice on my locust
tree. But after reading the answer to the the persons problem I see that the
spiderlike webbing on the leaves only at the end of limbs did not fit the Bark
Lice  in which the webbing is on the trunk and actual branches. I do not have
webbing on my locust tree in those places. I have also noticed a small limb
that has been dead for a while is now covered in white stuff. My locust is
about 2 stories tall. Do you know what this is, if it is harmful to the tree, and
how to treat it? Thanks,
Beth

Answer
Sounds like fall Webworm.
The fall webworm, Hyphantria cunea (Drury), is most often discovered when the unsightly, light gray, silken webs on the trees in late summer and early fall are observed. Webworms enclose leaves and small branches in their nests, unlike the tent caterpillars which make a smaller nest in the crotch of branches.

This pest is native to North America and is common from Canada into Mexico. It is one of the few American insect pests that has been introduced into Europe and Asia.

This pest usually eats leaves late in the season and the nests are generally concentrated to limited areas. Because of this, little real damage is done to most trees. However, the nests can look very unsightly and multiple generations in long summers can lead to significant defoliation.

Pruning to remove webs when they are first noticed is one possible control. Because caterpillars remain in the tent, time of day is not important. Sprays can be used for control but they must be applied with sufficient pressure to penetrate the silk tent and reach the leaves within. Appropriate insecticides include Bt, diazinon, Orthene or Sevin. Read and follow label directions.