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How to minimize moth mayhem.

There are steps a woodland owner can take, from species selection to spraying. Here are details.

Over the last century, the gypsy moth has become established as a major pest of hardwood forest in the Northeast and Michigan. Scientists have acknowledged for years that eradication is not possible, and have urged landowners to learn to cope with the gypsy. Here are some options for doing just that.

Experts agree that a landowner's first step be to assess a wood-lot's susceptibility and vulnerability to damage.

Susceptibility is a measure of the likelihood that the woodlot will be defoliated once gypsy moths arrive. The species of threes is the single most important factors determining susceptibility. A forest composed of 60 percent preferred food species (see accompanying list on page 44) is considered to have medium susceptibility; 40 percent is low; 20 percent is considered resistant to defoliation.

Other factors that increase susceptibility are dry, rocky, or sandy sites with thin duff layers, stress from drought and late frost, and recent disturbance by logging, fire, grazing, or storms.

Vulnerability refers to the degree of damage that defoliation will inflict on a tree or a forest. Vigorously growing trees with healthy crowns that reach to the main canopy usually won't die unless heavy defoliation (more than 60 percent of the crown) occurs several times. Much more vulnerable are trees that are suppressed beneath the main canopy; under stress from drought, late frost, or injury; or situated in areas commonly impacted by the two organism usually responsible for death after defoliation - shoestring root rot (Armillaria mellea) and the two-lined chestnut borer (Agrilus billineatus).

For woodlots that are susceptible and vulnerable, owners should weigh the costs and benefits of the following activities against their own individual management objectives. It is advisable to consult a private or state forester in designing detailed prescription for a specific site.


Kurt Gottschalk and Mark Twery, research foresters at the Forest Service's Northeastern Forest Experiment Station in Morgatown, West Virginia, suggest that management strategies that reduce the oak component to about one-third of a stand and promote a mixture of species and age classes are likely to keep some of the benefits of an oak forest while reducing the intensity and duration of gypsy-moth outbreaks. The treatments described below will accomplish what the moths would eventually do anyway. "But," says Twery," these techniques will allow more human control over it."


Since thinning and other intermediate cuts produce considerable stress that may last up to five years - thereby increasing a woodlot's susceptibility and vulnerability - such treatments are recommended at least five years before a moth invasion is expected. Harvest should focus on removing susceptible species and vulnerable trees and increasing stand vigor. Very young stands are not attractive to gypsy moths, so if adequate regeneration is established in a mature or nearly mature stand, harvesting the timber will set succession way back.

Since white pine in the understory of an oak forest is quite vulnerable, but a stand dominated by pine has low susceptibility, removing the overstory will allow a conversion to pine. Building brushpiles out of tops and limbs of harvested trees and retaining snags for den trees improves habitat for the many small mammals and birds that prey on the moth.


If defoliation is expected within a few years or is occurring already, a regeneration cut that removes the oak canopy above regeneration that is already well established may be the only appropriate harvest activity. Otherwise, stress from cutting may increase mortality. If foliage protection is desired, a woodlot owner may hire private sprayers or participate in local programs that apply insecticides.

Three mortality occurs within one to three years after defoliation, so wait a couple of years and keep a close eye on what's happening in the woodlot in order to make appropriate salvage decisions.


Efficient salvage of dead trees, thinning of remaining susceptible and vulnerable lives trees, and shelterwood or conversion cuts to assure adequate regeneration are the main considerations after mortality is known. Stands with low stocking levels and low mortality might best be left alone until stocking increases.


Private landowners should contact state of Extension foresters to identify the local programs and individual options that may be available. Some insecticides are restricted and must be applied by a registered applicator.

Disparlure: This artificially produced gypsy-moth sex attractant is placed on bits of tape that are attached to trees or formed into flakes that are dropped by air. Disparlure disrupts mating activity in small, low-level gypsy populations.

Inherited Sterility: In this method, partly sterile gypsy-moth egg masses, produced in a lab, are dispersed on the ground or by air in areas of low moth populations. Males that hatch from these eggs mate native females, which then produce sterile eggs that do not hatch.

Mass Trapping: Traps containing the gypsy-moth sex attractant are distributed throughout areas of low populations, attracting males and thus reducing reproduction.

Parasites and Insect Predators: Thirteen non-gypsy-moth-specific and six gypsy-moth-specific parasites and insect predators are already established and moving along with the spreading moth populations. They may be introduced into a new moth outbreaks or augmented where they already exists to maximize their effectiveness at maintaining low moth levels.

Gypchek: Nucleopolyhedrosis virus (NPV) is a naturally occurring disease that attacks only gypsy-moth larvae. It is sprayed by air. Recent development of a UV-light-filtering carrier for Gypchek that protects that virus from deteriorating before it can be ingested by moths promises to increase the effectiveness of this method. Gypchek works on moth population of more than 300 egg masses per acre, considered a moderate level. However, it is available only in extremely limited quantities because it must be produced from five moths in a lab.

Bt (Bacillus thuringiensis): A naturally occurring bacteria that can be produced artificially, Bt is applied by air. When eaten by insect, it can kill many large of the order Lepidoptera, which includes all moths and butterflies. Bt is applied to moderate to high moth populations.

Dimilin (diflubenzuron): This chemical insecticide is sprayed by air. When eaten,it inhibits the development of the hard substance called chitin, which forms the exoskeletons of insects, the shells of crustaceans, and the cell walls of certain fungi. Death results. There are no toxic effects on other animals, including humans. Dimilin is considered the most effective control of gypsy moths. Like Bt, Dimilin is applied to moderate to high moth populations.

Seven (carbaryl): Seven is a broadspectrum organocarbamate compound. An effective contract and stomach poison, Sevin kills a wide range of insects including bees gypsy-moth parasites and insect predators, and aquatic invertebrates. Because of its non-target impacts and its long-term residual characteristics, Sevin's use against the gypsy has been greatly reduced by the development of moth-specific poisons.

Orthene (acephate): An organophosphate compound that kills on contact when sprayed, Orthene also acts as a systemic poison when injected in pellet from into trees. Like Seven, it affects a wide range of non-target species and remains in the environment for long periods. Wounds made to inject pellets may themselves cause significant damage to the tree.
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Title Annotation:gypsy moth
Publication:American Forests
Date:Mar 1, 1989
Previous Article:Taking AIPM at the gypsy moth.
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