Two common types of caterpillars make webs in trees. The Eastern tent caterpillar makes webs in the forks of the branches and are more of a problem in the spring.
Fall webworms make their webs on the ends of the branches and are prevalent in the late summer and fall. Fall webworms are the most visible since their webs are on the end of the branches. Their webs remain in the tree after the webworms leave.
Fall webworms can be up to 1 inch long. They come in two color forms. Those with black heads are yellowish-white while those with red heads are brown. Fall webworms are covered with long, soft gray hairs.
Fall webworms will feed on more than 100 types of trees but they prefer trees like pecans, black walnut, mulberry, elm, sweetgum, willow, apple, ash and oak. I see them most often in pecan trees.
The caterpillars form fine silken webs on the ends of the branches. They will enlarge the webs if they need more leaves. They feed on the leaves in these webs for a couple of weeks before they leave the trees to become pupae.
These pupae eventually turn into white moths that have black spots. These moths fly away to lay eggs on trees to start another generation of webworms. There can be up to four generations of fall webworms in a year. Webworms survive the winter as pupae in cocoons in protected places.
Although these caterpillars feed on the leaves of the tree, the tree should recover. Healthy trees are able to withstand a great deal of insect damage to their leaves without lasting injury. I would not be concerned about fall webworms feeding on healthy trees; however, severely weakened trees may be damaged or killed.
Healthy trees can usually stand the loss of almost all their leaves and still live. This is true of most deciduous trees (trees that lose their leaves in the fall) but not needled, evergreen trees like pines, cedars, junipers and other conifers.
Evergreen trees with needles cannot withstand the loss of their leaves and must be better protected against loss of leaves. Fortunately, webworms attack needled evergreen trees less frequently than broadleaf trees.
Since most trees will not die from caterpillar attack, spraying is generally not required. If you want to control the caterpillars by spraying, you must treat the entire tree - perhaps more than once. You may need to hire a tree service to do this.
When treating the tree, it will be necessary to get the insecticide inside the webs to kill the caterpillars. For these reasons, it is suggested that we just live with these worms for a while. They will eventually leave.
If you do decide to spray; use insecticidal soap, horticultural oils or Bacillus thuringiensis (Bt) to kill small caterpillars. These insecticides are less likely to kill the natural predators that keep the levels of these webworms at low levels. These materials, however, are not as good at killing large caterpillars.
Watch the southern-most branches of trees in early spring to find the webs before the caterpillars get large. For larger caterpillars, use a chemicals like bifenthrin, cyfluthrin or Sevin. Once again, find a way to get the insecticide into the webs for best control.
Some people simply cut off or remove the branches where webs are located. This may actually damage the tree more than the caterpillars would. For this reason, it is better to tolerate fall webworms for a while and they should go away on their own.
Randy Drinkard is a technical writer for The UGA Center for Urban Agriculture and ANR agent for Troup/Meriwether Cooperative Extension. The Troup County Extension office is located at 114 Church St., can be reached at 706- 883-1675 and is open Monday through Friday, 8 a.m. to 5 p.m.