WV Gypsy Moth Damage Assessment Report 2005

In 2005, the West Virginia Department of Agriculture initiated a gypsy moth damage assessment to evaluate the tree mortality associated with the record defoliation from 2000 to 2002. To download the report, click on the link below:

The gypsy moth is potentially the most destructive forest pest threatening West Virginia woodlands. Since its inadvertent introduction into Massachusetts in 1869, it has spread naturally south and west at approximately 5-10 miles per year. In the last 10 years, it has been spreading across the eastern panhandle and northern counties of this state. It is presently concentrated in Jefferson, Berkeley, Morgan, Hampshire, Hardy, Pendleton, Grant, Mineral, Tucker, Randolph, Pocahontas, Preston, Taylor, Barbour, Monongalia, Marion, Hancock, Brooke, Ohio, Marshall, Wetzel, Harrison, and Upshur counties.

In the northeastern states, gypsy moth populations peak every 8 to 11 years. They feed on more than 500 different tree and shrub species in forest and urban areas. Repeated heavy defoliation by gypsy moths leads to the death of trees. Spruce, pine and hemlocks die after one heavy defoliation. Hardwood tree mortality after two successive years of defoliation, can reach as high as 80%.

There are five essential steps in minimizing gypsy moth impacts:


Gypsy moths attack trees by feeding on their leaves. Severe defoliation and mortality are most likely in stands having a high percentage of oak, the favorite food of gypsy moth caterpillars. Generally, if 60 percent or more of a hardwood tree's foliage is removed, the tree will, later in the same growing season produce a new set of leaves. This places a heavy demand on the tree's food reserves and makes it more vulnerable to attack by other organisms. This significantly increases tree deaths.

Based upon evaluations of gypsy moth mortality in West Virginia, the Division of Forestry has developed guidelines for estimating the potential mortality that can be expected following one, two or three consecutive years of gypsy moth defoliation. These guidelines are simply a rule-of-thumb and may not account for all of the variation in damage that may be caused. The extent of mortality will be affected by many interrelated factors like frequency and intensity of defoliation, tree stress, actions of secondary organisms such as shoestring root rot and the two-lined chestnut borer, influence of gypsy moth parasites and predators, effectiveness of control measures and weather conditions. Each of these factors are in themselves difficult to predict. Although not perfect, the guidelines do provide an indication as to where severe impacts are most likely to occur.

Using these guidelines, your timber stands were assigned hazard ratings for potential mortality from gypsy moth. (Guideline for Determining Gypsy Moth Hazard Rating).

Now that you know WHERE severe impacts can be expected you need to know WHEN control actions are needed.


Treatments to control gypsy moth are needed when gypsy moth egg masses reach or exceed the following levels. Such numbers will seriously impact your management objective:

Timber 1,200
Aesthetics 650
Wildlife - Mast Production 500
Recreation - Nuisance Prevention 250

Inspect your woodland for egg masses sometime after the leaves drop in the fall each year. If they are found, count the number on a 1/40 acre plot. You only want to determine the number of new (current year) egg masses per acre. New egg masses are brightly colored and firm to the touch. Old egg masses are faded and spongy. To do this, step off a rectangular plot 27 feet by 40 feet. Count the number of new egg masses on trees, stumps, down logs, etc. in this area and multiply by 40 to obtain the approximate number of egg masses per acre. Egg mass counts should be made in no less than ten plots located in the stands having moderate to high gypsy moth hazard ratings. Average the per acre egg mass counts and if you find 1,200 or more egg masses you can expect moderate to heavy defoliation and subsequent tree mortality unless you apply control measures to the stands. Lesser numbers, as shown by the above table, also cause problems. It should be noted that the West Virginia Department of Agriculture will conduct egg mass surveys on your property upon request.


Spraying is rather expensive, but well worth the money to protect high value sawlog and veneer quality trees and stands where moderate to high tree mortality is expected.

Contact your local service forester, consulting forester, or entomologists in the West Virginia Department of Agriculture, Plant Industries Division for specific control recommendations. You may be eligible to participate in the State-operated control program. If not, you will be provided with a list of aerial applicators who will treat your woodlands for a fee. Spraying must be done in May to early June when the caterpillars are small.

The West Virginia Department of Agriculture (WVDA) coordinates and conducts a cooperative regional suppression program between landowners. The county commissions in the generally infested counties. Aerial spraying is done on a demand basis to minimize forest damage. Sign-up for the program is through the WVU County Extension Office in any of the participating counties during July and August.


Silvicultural treatments can be used in advance of gypsy moth infestation to minimize gypsy moth impacts. Such treatments decrease the susceptibility to defoliation and strengthen the stand against tree mortality. Healthy, vigorous trees are more likely to survive and recover from gypsy moth defoliation and to resist attack by secondary organisms. Thinnings will strengthen the stand against mortality by removing high risk trees before they are defoliated and die. High risk trees are low vigor trees with poor crowns.


Despite your precautions, if the gypsy moth is allowed to feed, some trees will die within one to three years after defoliation. Unfortunately, the value of veneer trees disappears as soon as they die and dead sawtimber trees lose 10 to 15 percent of their value each year they are dead because of drying checks, wood decay and wood borer defects. If possible, the salvage and utilization of dead timber will reduce the economic loss. However, the utilization of dead sawtimber trees is feasible for the first two to three years after death, and it is preferred that they be salvaged within the first year after death. Dead trees can be used for pulpwood for at least five years after death.


It should be noted that a gypsy moth regulatory program does exist although it does not directly affect most landowners. The program monitors the intrastate and interstate movements of gypsy moth regulated articles from gypsy moth regulated areas to presently noninfested counties. Articles include nursery stock, cut Christmas trees, logs, mobile homes and outdoor household articles. More information can be obtained by calling your county Extension Agent or a local WVDA representative.

* Guidelines For Determining Gypsy Moth Hazard :

50% + HIGH 25% +
21-49% MODERATE 11-24%
11-20% LOW 5-10%
0-10% VERY LOW 0-4%

For more information on Gypsy Moths:

West Virginia Department of Agriculture

Gypsy Moth Slow The Spread Foundation, Inc.

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