Ohio Oak Tree Blight

Oak Wilt

• Oak wilt has been reported in most of Ohio’s 88 counties, notes Ohio State University Extension. Oak trees in the red-black group, including blackjack (Quercus marilandica), scarlet (Quercus coccinea), pin (Quercus palustris) and shumard (Quercus shumardii) can die within weeks of contracting the disease. White group oaks such as post (Quercus stellata), bur (Quercus macrocarpa) and chinquapin (Quercus muehlenbergii) may survive one year or more, but the disease take its toll on the trees. Fungal spores spread with water into tree tissue, choking the vascular system. Fungi can also travel with insects or spread from neighboring tree roots. As oak wilt progresses, canopy leaves become reddish brown -- red oak foliage then turns yellow, but white oak leaves are bland with dead spots along the veins. Trees infected in the spring show wilting leaves by mid to late summer. Oak tree wilt can be managed if pathogens are kept from spreading.

Pin Oak Blight

• Pin oak blight develops from the Endothia gyrosa fungus, which enters trees through broken limbs and pruning scars. Although fungal spores spread to different varieties, Ohio pin oaks and other species in USDA zones 5 and 6 are especially susceptible. The disease may cause cankers that prompt leaves to curl and drop. Trees may also develop chlorosis, the yellowing of leaves caused by the lack of chlorophyll, because of injured roots or nutrient deficiencies in the soil.

Oak Leaf Blister

• Oak leaf blisters are caused by the Taphrina caeruescens fungus in all varieties but especially in pin and white oak trees (Quercus alba). Severe infections cause leaves to fall, usually by midsummer. Light green blistering patches develop on leaves. Fungal spores germinate in spring, infect the leaf and develop blisters. Fungicidal treatments usually do not work well on mature oaks, advises Clemson University Extension, but they may help smaller trees when applied in the spring.

Oak Diseases and Pests

• Among many diseases, oak trees in Ohio and all areas of USDA zones 3 through 11 may contract anthracnose (Apiognomonia quercina), a leaf blotch that causes foliage to shrivel. Fungicides do not always work, but you can use a solution of mancozeb, chlorothalonil or thiophanate-methyl for possible control. Trees that cannot absorb adequate amounts of water may have bacterial leaf scorch, from the pathogen Xylella fastidiosa. Trees die gradually, usually within five to 10 years. Armillaria root rot, caused by the fungus Armillaria mellea, grows mushroomlike fruiting bodies at the base of oak trees, especially during wet weather. Powdery mildew, a grayish-white dusty substance on both sides of leaves, develops from a variety of fungi. Fungicides may be effective for some diseases, but removing infected trees and debris from planting sites is recommended. Oak trees attract many types of leaf-chewing insects such as caterpillars, moths, flies, spider mites and gall wasps. Insects may transport fungal spores between trees.