Webworms are the caterpillar form of a small white moth. The moths fly around during the summer laying their eggs on the underside of tree leaves. The moths seem to prefer alder, willow, cottonwood, apple, pear, peach, pecan, walnut, elm, and maples, but will eat a very large variety of trees and shrubs.
The fall webworm, Hyphantria cunea, is a moth in the family Arctiidae known principally for its larval stage, which creates the characteristic webbed nests on the tree limbs of a wide variety of hardwoods in the late summer and fall. The moth is native to North America, ranging from Canada to Mexico, and is one of the few insect pests introduced from North America into other continents all over the world. It now has occupied probably its entire range in Europe from France to the Caspian Sea in the east. It has also penetrated into Central Asia. It has spread into China, southern Mongolia, Korea and southern Primorsky Krai of Russia and is now considered holarctic in distribution.
One or two generations of the pest occur in a year. However, in Tennessee several generations may occur in a year. This pest tends to go through periodic population explosions. Outbreaks every four to seven years may last for two to three years.
The adult moth lays her eggs on the underside of leaves in ‘hair’-covered clusters of a few hundred. Eggs hatch in about a week. The caterpillars are highly variable in coloration, ranging from a pale yellow, to dark grey, with yellow spots and long and short bristle. The maximum length is 35 mm. Webs are progressively enlarged, and much messier looking than those of other caterpillars. Larvae feed inside the tents until the late instars. Very young larvae feed only on the upper surfaces of leaves. Later, they consume whole leaves. The larval stage lasts about four to six week. The larval stage of this pest skeletonizes and consumes leaves inside the protection of a tent-like web that they enlarge as they require additional food and grow. On shade trees webs usually occur on occasional branches. The fall webworm feeds on just about any type of deciduous tree. It feeds on almost 90 species of deciduous trees commonly attacking hickory, walnut, birch, cherry, and crabapple wherein leaves are chewed; in result the branches or the entire tree may become defoliated.
The fall webworm is a widely distributed native pest of shade trees and shrubs and appears from late summer through early fall. This species acts similarly to the eastern tent caterpillar, but the fall webworm constructs its nest over the end of the branch rather than at tree crotches. The large conspicuous webs contain caterpillars, dead partially eaten leaves, and fecal droppings.
This pest usually eats leaves late in the season and the nests are generally concentrated to limited areas. Although trees experience heavy damage from webworms in the fall, it is the summer defoliations that cause the most stress on the trees. Summertime is when pecan trees are actively developing their nut crop and storing food for the winter in their roots. By the time defoliations occur in the fall, the impact to the tree is minimized because it has stored its winter food and produced its pecans. Fall webworms in South Texas prefer pecan trees to most other trees, but will munch on mulberry, hickory, oak, willow or redbud just as readily. The webs are made by groups of caterpillars hatched from the same egg mass. Webworm caterpillars and moths are active at night when most of their predators (paper wasps, hornets, and birds) are inactive. The caterpillars feed on leaf material and leave the stems and veins behind. Although these caterpillars are hairy, they do not sting; however, they can cause an irritating rash if their hairs come in contact with human skin.
Webworms enclose small branches and leaves in their light gray colored webs. Constant infestations of individual trees will cause limb and branch diebacks. There are several chemicals that help to control the webworms, but they may not be practical due to the problems related to application complications in larger trees.
A sure and effective way of combating fall webworms was devised by C Tech Corporation in the form of their product Termirepel™. Termirepel™ is a non-toxic, non-hazardous, environment friendly insect and pest aversive. Majorly targeted at curbing the termite menace, it is 100% effective against host of other insects and pests like webworms, beetles, etc. Termirepel™ is available in liquid concentrate form which can be diluted further and made into sprays that can replace conventional harmful insecticides. The spray can then be just sprayed on the trees or plants affected.
Termirepel™ is also available in the form of lacquer which can be applied on the trees and the surrounding areas. Termirepel™ is unique in its aspect that it works by the mechanism of repellence and not by killing. Thus, target as well as non-targeted beneficial species are not harmed but are merely kept away from the application.