This is expected to be a bad year for gypsy moths

April 01, 2008|By ANNETTE IPSAN

Brace yourself. This is expected to be a bad year for gypsy moths. Last year, they rebounded after 20 years of low numbers to strip significant patches of forest and vex homeowners.

Gypsy moth caterpillars have tremendous appetites. These "walking stomachs" can strip a large tree of its leaves in days. Oaks are their favorite entreé, but they will dine on birch, apple, willow, sweet gum, linden, hawthorne, Colorado spruce and other trees.

Scientifically known as Lymantria dispar, gypsy moths do the most damage in areas heavily forested with their favorite trees. We saw outbreaks last year in homes surrounded by many mature oak trees next to parks and protected areas.

Most trees can handle a year or two of damage from gypsy moths, even if they strip off most of the leaves. However, it does weaken the tree, making it more susceptible to pests and disease. Factor in existing drought stress and you could lose a tree in a year.


Why are gypsy moth numbers surging? Biological controls that had been helping to keep their numbers in check aren't working as well. A fungus that naturally controls them won't work when it's dry. Several years of drought set the stage for a dramatic comeback.

Few predators and parasites control gypsy moths. They were accidentally introduced in 1869 by a scientist who was trying to breed an American silkworm. Since they're not natives, they have few natural controls. Birds won't even eat them because of their irritating hairs.

The Maryland Department of Agriculture (MDA) has successfully controlled gypsy moths in selected areas with monitoring and spraying since the 1980s. But without natural checks, their numbers skyrocketed in 2007. Although the MDA treated 50,000 acres statewide last year, many acres were defoliated.

This year, budgets allowed the MDA to propose spraying nearly 18,000 acres in Washington County. Homeowners in spray areas have been notified. Even so, we have been cautioned to expect some areas of high damage.

What can you do?

The first step is to understand the gypsy moth's life cycle and hit it when it's vulnerable. Eggs laid last summer won't hatch until mid-to-late April. So, you can still scrape them off trees and destroy them.

Gypsy moth egg masses are tan, oval, frothy and about the size of a quarter. Look for them on tree bark, the lower side of tree limbs, on firewood and tucked under lawn furniture and other man-made objects.

When you find egg masses, scrape them off with a knife. Then burn them, drown them in soapy water or put them in a sealed bag in your trash. Each egg mass holds about 1,000 eggs, so removal is important.

(Use gloves when handling the egg masses if you have allergies. The hairs of the caterpillars imbedded in the egg masses can cause a reaction.)

The best time to control gypsy moth caterpillars is in early May, right after they hatch and begin feeding. When they're small, they are vulnerable to an organic spray called Bt. Short for Bacillus thuringiensis, Bt is a naturally occurring bacteria. Used by the MDA, Bt kills the caterpillars by destroying their gut. It's a good organic control because it doesn't harm other insects or persist in the environment.

In addition to using Bt, the MDA is also spraying an insect growth regulator called Dimilin in some areas.

If your home isn't part of the state spray program and you want to protect your trees, you can spray your trees yourself with Bt or hire a professional. The MDA Web site (noted below) lists several certified aerial and ground applicators.

The Washington County Forestry Board offers another option if your property isn't sprayed by the state. This program delivers lower costs through group rates. There is a 20 acre minimum, but individuals can join with neighbors to create a qualifying area. Call George Epperling at 301-791-4733 by April 7 if you are interested in this program.

There are several other ways to control gypsy moths. You can apply sticky barrier bands to trees to trap young caterpillars before they enter the tops of your trees. Or, you can use hiding bands made of burlap to trap migrating caterpillars which you can remove and destroy.

Most of us don't notice gypsy moth caterpillars until they are large. By June, they are about 2 inches long with rows of blue and red dots along their very hairy black bodies. At this point, they are eating machines and can defoliate large trees surprisingly quickly.

Mature gypsy moth caterpillars also have rather large droppings which rain down prodigiously on your home, car, lawn and picnic tables. They are one messy and destructive insect.

You may never see a gypsy moth in your yard. Or, you might be inundated if you have many large oak trees or live next to a forest filled with favorite trees. The important thing is to be armed with information and an arsenal of controls to keep them from doing severe damage.

To learn more about gypsy moths and their control, visit the University of Maryland's Home & Garden Information Center Web site at Click on the plant diagnostics button and type in "gypsy moth" to locate a fact sheet with color photos and management tips.

You can also go to the MDA's Web site at You'll find information on everything from identifying and removing egg masses to treatment options and lists of certified pesticide applicators.

To locate the section on gypsy moths, click on "plants/pests," select "forest pest management," and choose "gypsy moths."

If you don't have access to a computer, send me a self-addressed, stamped envelope at: Gypsy Moth, MD Cooperative Extension, 7303 Sharpsburg Pike, Boonsboro, MD 21713 and I will answer your question.

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