Oak Wilt |
| USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus. |
Oak wilt, caused by the fungus Ceratocystis fagacearum, has been reported from the Lake States east to Pennsylvania and south to Texas. All oak species are susceptible to the fungus. Red oaks are more susceptible than white oaks and may die within a month after infection. Symptoms first appear at the top of the tree and progress downward. In the white oaks, a few branches usually die each growing season for several years.
Symptoms may appear any time during the growing season, but usually appear in early summer. Premature dropping of the leaves is a common first symptom in early summer. Premature dropping of the leaves is a common first symptom of oak wilt, but in the Lake States, infected trees often retain their leaves. The leaves usually crinkle and develop a black stem and a sharp line between green and brown leaf tissue. Some fallen leaves may be green toward the center and brown near the edges. Others may remain entirely green.
The fungus fruits asexually within the vessels of the tree, and the spores are carried throughout the tree in the transport system. Sexual fruiting bodies form in pads of black fungal material beneath the bark, causing breaks in the bark. The spores are sticky and cannot be blown to new hosts. Oak wilt is spread locally through root grafts with adjoining trees, and over long distances mostly by insects. Because some of these insects feed on sap that flows from wounds, wounded oaks are especially vulnerable.
Symptoms; leaf symptoms
Minnesota Department of Natural Resources Archives, Minnesota Department of Natural Resources |
Damage; fungal mat
T.W. Bretz, USDA Forest Service |
Symptoms; Oak wilt in a young group of pin oaks
Joseph O'Brien, USDA Forest Service |
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