Landscaping & Nursery Information for Home Gardeners



A single defoliation seldom kills a hardwood tree. Loss of one-half of the tree's foliage results in little more than a reduction in growth. However, when most of the foliage is lost, the tree doesn't have the ability to produce growth. Stored food in roots are at the lowest. The plant has difficulty producing additional leaves to compensate for those lost. The tree's effort to re-foliate itself in the summer strains the root system and usually results in twig, branch and bud death during the winter. If Gypsy Moths defoliated plants in the fall, few trees would be lost. Repeated loss of leaves over consecutive years usually spells the end of the tree. A single defoliation of a conifer, however, can result in tree death.

Tree death can occur following a single year defoliation if the specimen is suffering drought stress or is on a poor site.

Many trees don't succumb directly due to defoliation but by secondary invaders that attach the weakened tree. These can include other insects, diseases or environmental conditions such as drought or floods that can cause fatal injury.

Efforts should be made to keep affected and unaffected trees in a healthy state. Affected trees should receive adequate mulching, watering and fertilizing to help them recover. Judicious pruning might reduce stress on the plant. Planting of less susceptible tree species should also be encouraged.

The major source of Gypsy Moth disbursement in the United States is through motor vehicles. A vehicle and plant materials from Gypsy Moth infested areas should be checked thoroughly for any signs of the insects including egg, larva, pupae and adults. Visual inspection may involve examinations of a vehicle's underside, joints or hitches. Both sides of wheels should be checked.

Control is difficult and controversial. Chemical control is effective but requires community support and action. Community-wide spraying usually runs into opposition and is costly.

Egg masses should be removed and placed in cans of rubbing alcohol, bleach or kerosene to prevent hatching. Just scraping eggs off the trees and onto the ground does not reduce the population significantly. Most chemicals painted on egg masses have little effect on the masses and can damage the cambium layer of the tree. Banding trunks with substances such as Tangle-Foot seem to have little control on infested trees. Some success can be achieved on sprayed or non- infested plants. Contact the Illinois Department of Agriculture (IDA) before controlling any of the stages.

Chemical control in Illinois is on the advice and assistance of the Illinois Department of Agriculture.

The Illinois Department of Agriculture annually conducts survey of Gypsy Moth activity using phermore traps. Visual surveying of egg masses also provide information on potential outbreaks.

If any Gypsy Moth egg masses, caterpillars or moths are found, notify the Illinois Department of Agriculture immediately.

See: Gypsy Moth--Identification; Gypsy Moth--Hosts


Oaks (Quercus) are the preferred host, though other susceptible species include apple (Malus), alder (Alnus), aspen (Populus), basswood or linden (Tilia), hawthorns (Crataegus) and willows (Salix) are also damaged. Beeches (Fagus), birches (Betula), cherry (Prunus), black or sour gum (Nyssa), hickory (Carya), hornbeam (Carpinus), maple (Acer) and sassafras. Even evergreen can be infested resulting is dead cedars (Juniper), hemlock (Tsuga), pine (Pinus) and spruce (Picea). However, ash (Fraxinus), tulip poplar (Lirodendron), locust (Robinia), walnut (Juglans), Dogwood (Cornums), Holly (Ilex), Fir (Abies), and sycamore (Platanus) are seldom attached.


Only the larval or caterpillar stage does damage. One two-inch caterpillar will eat one square foot of foliage every 24 hours. Seldom, though, do you find just one caterpillar; usually they occur in colonies over a million.

Gypsy moth eggs hatch in early spring. The resulting caterpillar is brownish black with a double row of blue-black and red dots along the back. The body is covered with groups or tufts of hair. Seldom are caterpillars over 3 inches long. Caterpillars drop from trees on silken threads, called "ballooning" much like cankerworms. Strong winds can pick up these threads and transport caterpillars over many miles.

Caterpillars feed approximately two months and then pupate. Two weeks later, brown males moths and white female moths emerge. Females seldom fly and are dependent on males locating them. Egg masses usually contain 1,000 eggs and are covered with buff colored hairs from the female's stomach. Moths live less than two weeks. There is only one generation per year.

Gypsy Moths are often confused with the Eastern Tent Caterpillar which emerges at the same time and can appear similar. However, Gypsy Moths DO NOT spin webs or tens.

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See also Garden Pests & Insects

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