By: Anthony C. Arnoldi, Board Certified Master Arborist WI-0102B
Gypsy moths are quite amazing creatures. They have spread across one third of the United States and are still gaining territory despite rigorous programs to slow the spread. They have been firmly established in Southeast Wisconsin for at least the last 5-7 years. For the first 3 to 4 years, gypsy moth damage was limited to a few “hot spots.” Last season, however, gypsy moth feeding damage was noted in nearly every neighborhood, sometimes lighter, sometimes heavier, but certainly gypsy moth presence is much more universal. We will look at the best way to stop the damage from this pest.
This is very important concerning the well-being of your trees, especially the large, mature specimens of slowergrowing species like oak, beech, ironwood and sugar maple.
They are injured quickly by significant feeding of the larvae on the leaves. These trees normally put out only one set of leaves in spring and if these are eaten, the tree must use its emergency set of buds and a large portion of its reserve energy to replace the leaves. This greatly stresses the tree and leaves it open to attack by other insects and disease. Even one complete defoliation might kill an oak outright.
The gypsy moth season is fairly short. Larvae (caterpillars) start to hatch from egg masses in early to mid-May. They are tiny at first—less than 1/8" long— and begin to feed. Because they are small, their feeding usually goes unnoticed. Their growth is rapid, however, and they will reach 2 ?2-3" with surprising girth by mid- to late-July, when feeding stops. It is in June and July that we get most of our calls from customers panicking that the leaves on their trees are “disappearing overnight” or that caterpillar droppings are “falling like rain” on their walks and patios. The larger caterpillars do eat a lot at a rapid pace!
When the caterpillars are large, they are robust; almost no predation by birds occurs because of their irritating stiff hairs filled with histamine. They are somewhat resistant to spraying at this time as well, although labeled preparations are available to do the job. The disadvantages to this are the potential drift of conventional pesticides and the fact that much feeding damage has already occurred.
The best strategy is to spray them in May when the caterpillars are still small. Then they are vulnerable to a bacterial preparation called Btk that is sprayed onto the foliage that the larvae are eating. When the caterpillars eat the Btk it disrupts their digestive system, stops them from feeding and eventually kills them. The advantages of Btk are: 1) it is a natural material that is virtually non-toxic to anything except certain young caterpillars; 2) it is much easier on the environment (an environmentally “soft” product); 3) it can be used in more varied situations, allowing more trees to be included in spraying; and 4) it kills the caterpillars before they damage the trees.
This, then, represents a very important “window” of time for treatment of gypsy moths. It is no accident that federal, state and local authorities utilize this same window for their efforts. In order to effectively battle this very important pest, we must stress the importance of being early, utilizing this window, and thereby benefiting your trees and the environment. Please call your Wachtel Certified Arborist for a determination of the extent of gypsy moth infestation and the appropriate response, before the ideal window for treatment closes.
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