Maryland Department of Agriculture

Maryland is currently experiencing the worst gypsy moth outbreak in a dozen years. Wooded areas of Cecil Harford, Baltimore, Anne Arundel, Howard, Prince George’s Montgomery, Carroll, Frederick Washington , Allegany and Garrett Counties are having problems with defoliation by the gypsy moth. This is despite the spraying of over 50,000 acres of public and privately owned land in May by the Forest Pest Management Program.

Many areas with current gypsy moth problems but which were not sprayed have turned out to be either areas known to have low – moderate population levels going into Spring 2007 or where no egg masses were observed prior to Spring 2006. Apparently dry weather the last two seasons has resulted in more caterpillars surviving to the large stage than usual, causing populations to surge and defoliation to increase. May 2007 was one of the driest Mays on record. Dry weather generally benefits the gypsy moth because it discourages the spread of the virus and fungal diseases that can infect a large percent of caterpillars.

Many residents and homeowners are seeking advice regarding combating the heavy populations on their properties. As of the middle of June, the gypsy moth caterpillars in almost all areas (except in Allegany and Garrett Counties) are nearly full grown and it is not cost effective to hire an applicator to spray with insecticides at this late stage. Homeowners may still wish to directly treat trees and shrubs that can be reached with a pump sprayer or to kill caterpillars by brushing them with a wire brush into a bucket of soapy water to drown. Employing burlap skirts or sticky tapes will accomplish little unless the caterpillars are removed and destroyed daily. However, these and other control techniques designed for the homeowner will be almost futile when there are high numbers of caterpillars in their own and surrounding yards.

If the Oak trees have been stripped of their leaves, the caterpillars will seek other food sources, including ornamental trees and bushes on your property. These can be protected by spraying with fast acting insecticides labeled for that use.

The best actions to take are those which preserve the health of your trees. Trees that have lost 60% or more of their leaves to the gypsy moth are at the greatest risk. These trees may re-foliate in another 3 weeks or so, and will be in a weak and vulnerable condition. Trees can benefit greatly from being watered with a slow trickle of water over several hours. Water flow should be slow enough so that there is not run-off, but that allows the water to pool and soak into the ground. Homeowners are encouraged to also seek the advice of an arborist or licensed Tree care expert.

We would like to know your location which will help us in planning and evaluating our gypsy moth egg mass surveys conducted this Fall. Please contact your local regional Forest Pest management office. To find the contact information for the office that serves your area, click on the Field Office Contacts choice on the left of this page.

Surveys of egg mass counts are conducted in each area as part of the selection process for proposing areas to treat in the following year (spray 2008). The number of areas treated will depend on the amount of available funding from the U.S. Forest Service and State and local sources.