Gypsy Moth
Gypsy moth is the most serious pest of oak trees. Gypsy moth prefers oak but will also feed on sweet gum, linden, willow, birch, apple, alder, boxelder, blue spruce and hawthorn. Adult female moths are white with black spots and cannot fly. They lay feltlike tan egg masses on trees, rocks or wherever they can crawl to. Eggs are laid in the early summer.There is one generation a year and winter is spent in the egg stage. Egg hatch begins in late April or early May depending on the temperature. Young caterpillars are black and chew small holes in the leaves. Feeding begins in early May, which is the best time to control the caterpillars. B.t. sprays are very effective on the small caterpillars. Large caterpillars may consume leaves to the midrib. Caterpillars grow up to 2 inches in length and have 5 pairs of blue dots and 6 pairs of red dots. They are more difficult to control than the young caterpillars.
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Frequently Asked Questions
Will the state spray my trees?
Maryland Department of Agriculture has already sent letters to homeowners who are included in the state gypsy moth spray program. If you did not receive a letter, your trees are not going to be sprayed by the state. MDA will be spraying 100,000 acres this year. Spray maps will be available on the MDA site on April 21st.
Will the county spray my trees?
We are unaware of any counties planning to implement spray programs. You will need to make arrangements with a commercial arborist to have your trees treated.
If I noticed gypsy moth damage in my neighborhood should I be concerned about my trees?
Yes. Consider having your trees sprayed. Given the drought conditions of last summer, trees are already stressed and therefore less able to withstand any defoliation. For detailed information read FS 242, “Gypsy Moth and the Homeowner”, or for a shorter version, HG 44, “Gypsy Moth”.
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When is the best time to treat my trees for gypsy moth?
Small caterpillars are the easiest stage to control. The best time to treat trees is in early to mid-May. Large caterpillars are harder to kill.
My trees are very large. How do I find someone to spray them?
Look in your phone book or online for a certified arborist in your area. Check with your neighbors to see if they want to have their trees treated too. The larger the area, the lower the cost per tree. Large areas can also be treated by aerial spraying. Click here for a list of licensed commercial applicators. In the search category, select “ornamental - exterior, or aerial”.
How will the commercial arborist manage my gypsy moth problem?
Arborists need to time their applications well and thoroughly cover trees. If large areas need to be treated and trees are tall, then aerial applications may be recommended. Under a wide variety of conditions (rainfall, population size, and age structure), well timed applications of B.t. (Bacillus thuringiensis, a microbial insecticide) have been shown to provide good levels of control and foliage protection. Bt poses fewer problems in watershed areas where Dimilin (an insect growth regulator) is a concern. Other effective materials that may be used are Conserve® or Confirm®.
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Can I do the spraying myself? What do I use?
We do not recommend that you try to treat trees yourself. Unless your tree is very small, you will not be able to get adequate coverage of the leaves. Bt is labeled for gypsy moth but the homeowner product does not last for more than a few days. Call our horticulture consultants or “send a question” for advice on specific insecticides. Commercial applicators are trained professionals that have the proper equipment, and have effective insecticides that are not available to homeowners.
I don’t have an oak tree. Should I be worried about other trees in my landscape?
Gypsy moth caterpillars prefer oak but will feed on many other trees and shrubs including sweet gum, linden, blue spruce, willow, poplar, birch, apple, alder, boxelder, and hawthorn.
I don’t want to use insecticides on my trees. What can I do?
First of all, destroy gypsy moth egg masses before April. Read MDA's publication on how to destory egg masses. There are two different banding methods; Barrier bands and hiding bands. They are both very labor intensive. Read FS 476, "Controlling Gypsy Moth Caterpillars with Barrier Bands" and also page 5 of FS 242, “Gypsy Moth and the Homeowner”.
When is it too late to spray?
If your tree is completely defoliated or the caterpillars have moved out of the tree to pupate (June), it’s too late to spray. Destroy the pupae that you find to reduce next year’s population. Beginning in mid-June, destroy egg masses as you see them.
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