Question
I live in Kansas City and it seems that a lot of the trees in the parks got this
illness. Now mine has it too. It looks like there are lots of little webs hanging
from branches, but not the tent worm kind, but more all over the tree, and I
have seen little worms hanging down from a thread like substance. My tree
now has blotchy yellow and brown leaves that are all dying and they drop to
the grass still interwined with the webs. I am concerned that my tree will die..
What does it have and will it kill my tree? Thanks, Saskia

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.
Fall webworm larvae have been known tofeed on over 85 species of trees in the United States.

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.

Mechanical Control - Removal of Nests - Small nests can be pruned out of small to medium trees. Monitor trees early to detect the nests when only several leaves are involved. These small nests can be easily crushed. Do not burn or torch the nests in trees as this may do additional damage to the tree.
Biological Control - Apply Bacillus thuringiensis (Bt) - The bacterial insecticide, Bt, is quite effective against fall webworms if it is applied when the larvae are small. Use formulations with UV protectants and thoroughly cover leaves next to nests. As these leaves are incorporated into the nest and eaten, the Bt will be ingested.
Chemical Control - Standard Insecticide Sprays - Most applicators attempt to "blow" the nest out of the tree with a strong jet of insecticide mix. While this generally works, more material is often used than is needed. Locate nests early and merely wet the nest and cover nearby foliage. As the larvae walk on the nest surface or incorporate new foliage, they will contact the insecticide. Second applications may be needed if additional generations occur. Appropriate insecticides include Bt, diazinon, Orthene or Sevin. Read and follow label directions.


Chemical Control - Use Systemic Insecticides - Extensive nests may occur in tall trees which are difficult to spray with ground equipment. These trees can often be treated with translocated systemics applied to the soil for root uptake or injected.