Forest tent caterpillar
A cousin of the eastern tent caterpillar, the forest tent caterpillar (Malacosoma disstria) prefers hardwoods like sugar maples and oaks. The term ‘tent’ caterpillar is a little misleading as these insects don’t construct large tent-nests in the crooks of trees. Instead, they spin pad-like structures on trunks and on branches where they go to rest and to moult.

Gypsy moth
Like the tale of the sorcerer’s apprentice, the gypsy moth (Lymantria dispar) is an example of an experiment gone horribly wrong. The moth was brought to the United States in 1869 in a failed attempt to start a silkworm industry. Escaping soon after, the gypsy moth has become, over the past century, a major pest in the northeastern United States and southeastern Canada.

Oak leaftier
The oak leaftier, Croesia semipurpurana (Kearfott) is an important Tortricidae moth in a complex of native species feeding in the early spring on oak foliage throughout the forests of Eastern North America.  Oak leaftier caterpillars (larvae) tend to favor red, scarlet, black, and pin oaks.

Oak leafroller
The oak leafroller, Archips semiferanus (Walker) is an important Tortricidae moth in a complex of native species feeding in the early spring on oak foliage throughout the forests of Eastern North America.  Oak leafroller caterpillars feed not only on red and scarlet oaks, but also on chestnut and white oaks commonly found along ridgetops.

Scarlet oak sawfly
The scarlet oak sawfly, Caliroa quercuscoccineae (Dyar) skeletonizes leaves of scarlet, black, pin, and white oaks in eastern North America. It is also called the oak slug sawfly because of the fact that the larvae are covered with a coat of slime that helps them adhere to foliage.

Other Insects: Spider mites

Diseases

Anthracnose
Anthracnose (Discula spp., Kabatiella apocrypta) is a name for a group of diseases caused by several closely related fungi that attack many of our finest shade trees. It occurs most commonly and severely on sycamore, white oak, elm, dogwood, and maple.  On oaks, small scattered brown spots or large light brown blotches form along veins. The leaves look scorched.

Oak tatters
Oak tatters is a relatively new condition that affects emerging oak leaves, causing them to appear lacy or tattered. It has been observed throughout the Midwestern United States, including Minnesota, Michigan, Wisconsin, Iowa, Illinois, Indiana, Ohio, and Missouri. This disorder was first reported during the 1980's in Iowa, Indiana and Ohio, but has been observed only in the last 10 years in Wisconsin and Minnesota.

Oak wilt
Oak wilt is a fungal infection affecting oak trees. All species of oak are susceptible with red oaks being particularly vulnerable. In red oaks, oak wilt is almost always lethal and death can occur in as little as one month. There is currently no known cure and the best way of dealing with oak wilt is to isolate and then destroy the affected trees. This disease has been discovered in 21 eastern US states with the heaviest damage occurring in the mid-west states surrounding the Great Lakes. However, oak wilt has been reported as far south as Texas.

Other Diseases: Powdery mildew  · Wetwood

Other Problems

Mistletoe
Broadleaf mistletoe absorbs both water and mineral nutrients from its host trees. Healthy trees can tolerate a few mistletoe branch infections, but individual branches may be weakened or sometimes killed. Heavily infested trees may be reduced in vigor, stunted, or even killed, especially if they are stressed by other problems such as drought or disease.