Drought, Oak Wilt and Gypsy Moth Make Devastating Impact

Between the gypsy moth and oak wilt there will be a huge loss of oak trees in the county very soon.

Susan Thiel, Unit Manager of the Forest, Mineral and Fire Management division of the local Department of Natural Resources (DNR), said many of the oak trees in the county are at or near the end of their normal life cycle of 80 to 90 years and any increase in stress will shorten their lives.

The trees have been dealing with dry conditions for several years which has already put some stress on them. This summer the trees are facing two additional sources of stress - oak wilt and gypsy moths.

Oak wilt kills trees rapidly. It is caused by a fungus which is transferred between trees in two ways. The fungus plugs the water-conducting system of the tree. To block the spread of the fungus, the tree produces gums and resins which also plug the system, causing the trees to die quickly. Oaks will die within a few weeks after becoming infected.

The fungus can be carried to new areas by sap-feeding beetles, which move spores from infected trees to freshly-wounded healthy trees. Wounding an oak tree whether accidental (lawnmowers) or intentional (pruning) between April 15 and July 15 can lead to oak wilt.

It can also be moved in firewood. Infected firewood can form spore-producing pads under the bark which attract sap-feeding beetles and who transfer oak wilt spores several miles.

Once a tree is infected the fungus is spread through interconnected root systems with nearby healthy trees. It is necessary to stop the movement of the fungus through the root systems, however, it is not easy. Cutting down the infected tree before severing the interconnected roots can actually speed the movement of the fungus into surrounding trees.

Generally once a tree is infected all the trees in the interconnected root system are doomed. The only way to stop the spread is to place a barrier, usually using a vibratory plow or trencher, in the ground to isolate the infected group, cut down the trees inside the barrier circle and immediately burn the trees or remove the bark completely from the area.

Thiel said this disease is more devastating than gypsy moths and is similar to the diseases that effectively wiped out elm and chestnut trees.

Gypsy moths defoliate trees and shorten their growth season dramatically. As larvae they usually feed at night for four to six weeks growing until they are about two inches long.

About the end of this month they will turn into pupae and then emerge as moths in early August. While in the moth stage they do not eat, however, the female will lay egg masses which contain between 50 and 1,500 eggs which sit for nine months until they hatch out the following spring continuing the cycle.

One of the best ways to control the moths is to destroy the egg masses which are intertwined in a matting of hair from the body of the female and located in a protected area such as a loose flap of bark or something flat nailed to a tree. They can be scraped from the surface to which they are attached into a receptacle and then buried or burned.

When found in the caterpillar stage, one inexpensive way to get rid of them is to tie a dark-colored cloth band around the tree. The band should be about 12 to 18 inches wide and long enough to encircle the tree. Tie the middle of the band about 4-5 feet above the ground, then fold the top of the band down over the twine to form a band that is only 6-9 inches high.

Caterpillars tend to hide during the daytime and will often be found hiding under the flap. They can be easily killed by scraping them into a bucket of soapy water.

Thiel added that due to their age and the threats described above several stands of oak are scheduled for clear cutting both to help prevent the spread of oak wilt and to allow the forest to regenerate in oak. She said that if the stands were select cut, not only would it be harder to prevent the spread of oak wilt, but much of the new growth would be red maple which is a very aggressive grower, crowding out the more desirable oak.