Oak blight or oak wilt is a fungal disease that destroys thousands of trees annually in the United States in areas where the disease is common. The disease is so severe that it kills some species of oak in as few as three weeks. Although oak wilt has been reported in New York, as of March 2010, the U.S. Forest Service reported that infections had been controlled and the disease eliminated.
The earliest reports of a wilting disease of oak trees occur as early as the 1800s, and in 1942, the culprit was discovered to be a fungus. Oak wilt remained isolated throughout the 20th century in the upper Midwest and Texas, though the disease routinely devastated oak populations in those areas. In the summer of 2008, however, homeowners in Schenectady County, New York, reported wilting and death among oak populations. Investigation by the Cornell Cooperative Extension revealed the cause to be oak wilt.
According to the American Phytopathological Society, oak wilt has been reported in 23 U.S. states and 860 counties, primarily in the Midwest and Texas. In New York, infections were reported in a suburban area roughly the size of three city blocks. Prior to that point, the nearest reported case of oak blight had been Erie, Pennsylvania, more than 200 miles away.
Oak wilt is caused by a fungus that invades the tree's vascular tissue and blocks movement of the water from the roots to the leaves, accounting for the wilted look of the leaves followed by death of the tree. While the Cornell Cooperative Extension reports that all oak trees found in New York are susceptible, red oaks are most susceptible. The disease spreads through contact between roots underground and by insects that, attracted to the sweet-smelling fungus, carry the disease to wounds found on healthy trees.
Immediately after discovery of oak wilt in New York, the Cornell Cooperative Extension requested homeowners to observe their trees and send samples from any trees that appeared infected. If an infected tree is identified, the tree must be removed and the wood split and covered for at least a year. The extension further advises New York residents to avoid pruning oak trees between April 15 and July 15, when they are most vulnerable to infection from disease-carrying insects. Finally, propiconazole is approved for use in New York and, injected by an arborist, may prevent infection or treat infection in some trees.
The New York State Department of Environmental Conservation and the U.S. Forest Service worked together to eradicate oak wilt in New York by identifying, removing and chipping infected trees. They were successful, and in a report posted in March 2010, Robert Fitzhenry of the U.S. Forest Service reports that oak wilt has been eliminated from New York.