GARDEN GUIDE: Fall webworms indicate season is around the corner

Aug. 27, 2014 @ 04:58 AM

A sure sign that fall is around the corner is the fall webworms that can be seen around Lee County. Fall webworms congregate in webs formed toward the ends of the branches of over 600 kinds of trees, shrubs and other plants. More commonly in North Carolina, they prefer pecans, persimmons, sourwoods and willows.

The web starts at the branch tips and becomes enlarged to encompass fresh, green leaves until the web may become two to three feet long. Small trees infested with several broods of caterpillars may be entirely enclosed in webs. After feeding for four or five weeks, the caterpillars crawl down, spin cocoons and pupate in mulch or soil. Some confuse tent caterpllars for webworms. Tent caterpillars do damage in the crotches of the trees they inhabit rather than the ends of branches.   

Since caterpillars are chewing insects, the damage that occurs is chewed leaves and gradual defoliation. Because fall webworm damage accrues over the summer, they usually cause little long-term health damage to the trees they defoliate. 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.

There are two or three generations of fall webworms each year in North Carolina, depending upon how early or late in the spring the first race emerges. White fall webworm moths (some moths have small black spots) 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, so it is best to treat as soon as the webs are first noticed. A product containing Bacillus thuringiensis or carbaryl is appropriate for homeowner use, while commercial applicators can use B.t. (e.g., Dipel) or Conserve. As far as fire goes, do your trees and neighbors a favor and abstain from trying to burn the webs out of the trees. This is a dangerous practice and not worth the risk of playing with fire!   

For more information regarding Fall webworms and other garden pests, please contact the Lee County Center of North Carolina Cooperative Extension at (919) 775-5624.