City of Madison Logo
The gypsy moth was brought to North America in 1869 by Mr. L. Trouvelot in a misguided attempt to breed a hardy silkworm. Some escaped and the first recorded defoliation by gypsy moth was in 1889 of the street trees in Trouvelot's own neighborhood of Medford, Massachusetts.

Lacking many natural enemies, the gypsy moth has escalated into the most important insect pest of forest and shade trees in the eastern United States. They have moved steadily westward ever since, reaching Wisconsin in the late 1980s.

Each year, gypsy moth caterpillars defoliate thousands of acres of hardwood forests throughout northeastern United States, including Wisconsin.

Between mid-May and early June, planes hired by the Wisconsin Gypsy Moth Suppression Program will be flying and spraying your property and near your property as part of a treatment program to reduce the population of this pest. The planes fly very low, about 50 to 100 feet above the tree tops. Spraying may begin at dawn, and the spray may give off an odor until it dries.

The City Forestry section is working in cooperation with the Dane County Gypsy Moth Coordinator, elected officials, neighborhood residents and the WI DNR to track and attempt to suppress gypsy moth. The City and County officials count and record egg masses in the fall and use that data to apply for a DNR grant for aerial spray applications in the spring.


Gypsy Moth Life Cycle
April/May: The caterpillar (larva) hatches from the eggs in late April through early May and begin to feed. The caterpillars feed on oaks, crabapple, linden willow, birch and 250 other tree species. They can seemingly strip a tree of its leaves overnight. Gypsy Moth caterpillars do no build silk tents.

Late Summer: The caterpillar changes in the winged gypsy moth. Its sole purpose is to mate and lay eggs. The egg masses over-winter and hatch in the spring.

Recording Egg Masses
It is during this late summer and fall period when egg masses are counted and recorded on private and public land. Homeowners may find egg masses on their trees, house, fence, boat trailer, ... anywhere! Do NOT disturb the egg masses. Instead call the Forestry Section, 266-4816, so the egg masses can be counted and recorded. Only high-density areas and neighborhoods can be sprayed by the DNR.


Frequently Asked Questions
Why is the spraying done?
Gypsy moths feed on the leaves of many trees in residential and forested settings, and their populations can grow to the point that they eat all the leaves off of trees, which can kill trees in some cases. Surveys have shown that population of the pest in your area is large enough to cause extensive damage next June if no action is taken. The upcoming treatment was prompted by the requests of your community or residents within your community.

What insecticides will be used?
The aerial spray program will use an insecticide called ‘Foray’, a brand name for Bacillus thuringiensis kurstaki (commonly called Btk). The active ingredient in ‘Foray’ is a naturally occurring soil bacterium that kills gypsy moth caterpillars when they eat it. ‘

Does the spray hurt people?
Btk has been used for more than 30 years for gypsy moth control, and has undergone thousands of lab and field tests that demonstrate its safety. It is possible, but very unlikely, that people with severe food allergies or asthma may react to the spray. If you suffer from such conditions, you should take the simple precaution of closing your windows and staying indoors while the planes are spraying. The spray may give off an odor until it dries.

Does the spray hurt other animals?
Btk is harmless to all animals except caterpillars that feed in May. However, the planes may frighten pets or livestock, so you may want to keep them inside during spraying if possible.

Will the spray damage the paint on vehicles?
No. However, if you let Btk spray dry on your vehicle for several days, you may need to soak it with wet cloths for 15 minutes before washing it, or run it through the car wash twice (avoiding any wax application until the spray residue is removed).

When will spraying occur?
Each treatment area will be sprayed once between mid-May and early June (later in northern areas of Wisconsin). The exact timing depends entirely on the weather and growth of the caterpillars. Local media will be notified within 7-10 days before spraying, and again within 48 hours of the actual spray date. In cases where local media may not disseminate this information, the public can call a toll-free telephone number (1-800-642-MOTH) in May and June to find out when spraying will occur, and where the program plans to spray each day. Spraying may begin as early as 5:15am, and may continue into the early afternoon if weather conditions are suitable.

Why do you have to spray so early and fly so low?
The high humidity and low wind conditions typical of early morning are needed in order to assure the insecticide droplets do not evaporate and/or blow away before they land on the trees. Program managers also want to minimize the number of people active during spraying and avoid distracting commuters with low-flying planes.