Question
I have a large tree that has spider webbing wrapped around several tree branches.  What is this?  Is it dangerous for the tree?  If so, how do I deal with it?

I'm in West Houston, TX

Pamela


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.

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.

The large silk webs enclosing tips of branches are sure signs of fall webworms. The caterpillars remain inside the webbing, and if food runs out new foliage is encased. The caterpillars are covered with long white to yellowish tan hairs.

This pest overwinters in the pupal stage. Pupae are usually in the ground but can be located in old nest remains, under loose bark and in leaf litter. The adults emerge from late May into July. The eggs are usually deposited in a single (blackheaded race) or double (redheaded race) layer of several hundred eggs on the undersurface of leaves. The mass is lightly covered with scales from the female's abdomen. The eggs hatch in about a week and the small mass of caterpillars web over single leaves and feed by skeletonizing. As the caterpillars grow, they web over additional leaves and finally are able to eat the entire leaf. The larvae mature in about six weeks, at which time they drop to the ground to pupate. In southern states, adults can emerge in mid-March and up to four generations can be completed.

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.

Insecticide control:For shade trees spray trees with 0.25% malathion. (Mix 3 1/4 pts. of 57% malathion E.C. with 100 gal. of water; or 1 T/gal.) or 0.25% sevin (mix 2 1/2 lbs. of 80% sevin wettable powder with 100 gal. of water, or 2 T/gal.).  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.