We usually think of the fall webworm as a tree foliage pest of late summer/early fall. That is generally true. However, what was once thought to be a first generation may really be a different race of fall webworm that comes out earlier. There seems to be enough evidence from Kansas State University entomologists to support this hypothesis. True or not, and earlier than I remember, this week I've noticed the beginnings of fall webworm webbing on sourwood. Though it webs other trees, sourwood, pecan and persimmon are among its favorite hosts.Fall webworm damage accrues over the summer. They usually cause little long-term damage to the health of the trees they defoliate unless the trees are completely defoliated year after year. At any one location, the populations of fall webworms wax and wane so that they are conspicuous and damaging for a year or two and then the populations seem to disappear.Through the summer, the webs become filled with cast skins, droppings and dead leaves. The web is enlarged to encompass fresh, green leaves until the web may become two to three feet in length. Small trees infested with several broods of caterpillars may be entirely enclosed in webs. After feeding for four or five weeks, the caterpillars make it to the ground, spin cocoons and pupate in mulch or soil and continue the life cycle. There are two or three generations each year in North Carolina depending upon how early or late in the spring the first moths emerge. They overwinter as pupae in cocoons in the litter.White moths emerge to mate and lay 350 to 900 eggs on the lower leaf surface. The hairy caterpillars spin the webs as they feed. Fall webworms can be destroyed by pulling down the webs and destroying the caterpillars if the webs are in reach of a pole. If the webs are within reach of a hose-end sprayer, several insecticides can be sprayed for control. Insecticides work best when the caterpillars are young. Thus it is best to treat as soon as the webs are first noticed. If the trees are too tall for equipment used by the amateur horticulturist, many professional landscapers and arborists offer tree spraying as a part of their services. Bacillus thuringiensis and Orthene are two of several pesticides labeled for fall webworm control, but there are other choices.Ornamentals and Turf Insect Information Note No. 46 has additional information on the control of fall webworms (see http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note46/note46.html). You can also view a short QuickTime clip accessible through the Internet at:http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note07/fallwebworm.MOV.
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