Through good forest management practices, land managers can decrease the likelihood and severity of defoliation during a spongy moth (Lymantria dispar) outbreak. These practices improve stand vigor, giving trees a better chance of survival following defoliation. This publication describes management options for woodlots dominated by oaks and other deciduous trees.

Should you spray?

Your decision to spray should be guided by three considerations: how you use your woodlot, the predicted severity of defoliation, and the expense of treating.

Woodlot use

Conifer pulpwood production. Conifer plantations are best protected by removing preferred host trees, such as oak, witch hazel, amelanchier, and aspen, from their borders and understory.

Aesthetic or recreational use. Since appearances are important, you may wish to suppress spongy moth outbreaks in your woodlot, especially if your home is there. The cost of spraying may be significant but it is probably less than the cost of removing dead trees from around your house.

Hunting. Oaks are an important source of food for many game animals and defoliation will reduce acorn crops for several years. Hunters may wish to protect their acorn crop by suppressing spongy moth outbreaks.

Providing habitat for non-game wildlife. While some trees may die as a result of defoliation, they will go on to provide important nest and den snags for cavity-dependent species. Because our younger forests often have few snags, the formation of dead material following an outbreak of spongy moths can actually help increase the diversity and abundance of bird populations. Landowners whose primary interest is nongame wildlife may decide to allow outbreaks to go unchecked.

Predicting defoliation

You can predict next year’s level of defoliation by spongy moth caterpillars by conducting a simply survey and counting the number of egg masses on your property. Survey instructions can be found here.

Economic considerations

Even if more than 50% defoliation is predicted for your woodlot, it may not make economic sense to treat. In the first year of defoliation, weak trees die. This can be a benefit if your woodlot is overstocked with many suppressed trees. When these weak trees die, the remaining trees face less competition for sunlight, water, and nutrients. In Pennsylvania, researchers found dramatic increases in growth of red oaks following an attack by spongy moth. On the other hand, in a stand dominated by very old white oaks already suffering from some crown dieback, severe defoliation will kill many of these trees. Treatment will be essential to save the stand.

To decide whether treatment makes sense for your situation, consult a Wisconsin DNR forester.