How to Treat Oak Tree Disease in Pennsylvania

Will it Wilt or Will it Not?

• Nearly all oak trees in Pennsylvania are susceptible to oak wilt but red oaks (Quercus rubra), hardy in U.S. Department of Agriculture plant hardiness zones 4 to 8, northern pin oaks (Quercus ellipsoidalis), hardy in USDA zones 4 to 7, and shumard oaks (Quercus shumardii), hardy in USDA zones 5 to 9, are the most highly susceptible oak tree species. White oaks (Quercus alba), hardy in USDA zones 3 to 9, and bur oaks (Quercus microcarpa syn. Quercus texana), hardy in USDA zones 6 to 9, are not as susceptible but can still be infected.

Careful with that Weed Wacker

• Oak wilt is a fungal infection that commonly enters healthy trees through wounds. Beetles and other insects carry the fungus from diseased trees to nearby wounded trees. It can also spread through natural root grafting between healthy and diseased trees. Insects can spread the disease to oak trees farther away when the infected, insect infested wood is transported for firewood or other uses.

That is Not Fall Foliage

• Symptoms begin at the top of the oak tree when the foliage turns brown along the edges, wilts and drops from the tree with a small amount of green leaf color at the center of the leaves. Twigs and branches die as the symptoms continue down the tree. Sapwood in the branches may have brown streaks and, when cut in two, the outer growth ring visible at the cut end may be brown. Infected oaks in Pennsylvania commonly begin to show symptoms from late spring through summer.

Don’t Panic

• Before beginning treatment, the oak wilt disease should be confirmed by an experienced arborist. Oaks in Pennsylvania are susceptible to other diseases and environmental disorders that have similar symptoms. Anthracnose, for instance, which is also caused by a fungus, has similar symptoms except that the lower branches and foliage begin to decline first. Insufficient and excessive moisture can also cause similar symptoms.

Divide and Conquer

• After the diagnosis is confirmed, a 3-foot deep trench must be dug between the sick oak and other trees to sever roots that have naturally grafted together. The trench should be at the halfway point between the sick oak and healthy trees that are less than 50 feet away. When more than 30 percent of the tree is showing symptoms, it should be removed. The wood and stump should be buried or burned immediately to prevent possible spreading of the disease by boring insects. Nearby trees that have not been infected or are showing symptoms in less than 30 percent of the tree can be injected with propiconazole to slow down the disease or help prevent infection. These injections are done by professional arborists.

  Reduce the possibility of future oak wilt infections by pruning oak trees in Pennsylvania between November 1 and April 15. During this time the boring insects and fungus are not active and will not enter healthy oaks through pruning wounds. Always sterilize pruning tools before and after use, using a disinfectant such as rubbing alcohol or a solution of nine parts chlorine bleach to one part water.