Injury – white The disease symptoms are much more variable in white oaks, although oak: the foliage symptoms are often the same. In a few, particularly bur oaks, symptoms are essentially the same as in the red oaks, and the tree may die within one growing season. Usually, however, white oaks die slowly. Only one or two branches may show symptoms and die in a year. If the fungus persists, a few branches are killed in a season. Over several years, the tree declines and may die. Some white oaks seem to recover from the disease, but may harbor the pathogen and serve as reservoirs without symptoms. White oaks, unlike the red, frequently have discolored infected annual rings when diseased. Fungus mats seldom appear on white oaks. Natural root grafts and insect vectors spread the oak wilt fungus from diseased to healthy trees. Healthy oaks growing next to infected ones become infected through their roots. Root grafts offer a path to transmit the fungus and are a major factor in the spread, especially in areas with deep, sandy soils and dense, pure stands of red oaks. The fungus over-winters as mycelium in living, infested trees. It as fungus pads on dead trees. The fungus can be spread more than a mile by at least two groups of insects: sap and bark-feeding beetles. When the fungus mats enlarge and crack the bark, the emitted odor attracts insects such as sap-feeding beetles. When the beetles feed on the mats of the infected tree, fungus spores adhere to their bodies. As the beetles move from diseased trees to wounds on healthy oaks, the disease—causing spores are transmitted to a new host. Figure 2: Symptoms on red oak leaves Figure 3: Oak wilt symptoms Figure 4: Fungus mat (24-022) Species: Ceratocystis ulmi Host: American elm
Injury – white oak: The disease symptoms are much more variable in white oaks, although the foliage symptoms are often the same. In a few, particularly bur oaks, symptoms are essentially the same as in the red oaks, and the tree may die within one growing season. Usually, however, white oaks die slowly. Only one or two branches may show symptoms and die in a year. If the fungus persists, a few branches are killed in a season. Over several years, the tree declines and may die. Some white oaks seem to recover from the disease, but may harbor the pathogen and serve as reservoirs without symptoms. White oaks, unlike the red, frequently have discolored infected annual rings when diseased. Fungus mats seldom appear on white oaks. Natural root grafts and insect vectors spread the oak wilt fungus from diseased to healthy trees. Healthy oaks growing next to infected ones become infected through their roots. Root grafts offer a path to transmit the fungus and are a major factor in the spread, especially in areas with deep, sandy soils and dense, pure stands of red oaks. The fungus over-winters as mycelium in living, infested trees. It as fungus pads on dead trees. The fungus can be spread more than a mile by at least two groups of insects: sap and bark-feeding beetles. When the fungus mats enlarge and crack the bark, the emitted odor attracts insects such as sap-feeding beetles. When the beetles feed on the mats of the infected tree, fungus spores adhere to their bodies. As the beetles move from diseased trees to wounds on healthy oaks, the disease—causing spores are transmitted to a new host. Figure 2: Symptoms on red oak leaves Figure 3: Oak wilt symptoms Figure 4: Fungus mat (24-022) Species: Ceratocystis ulmi Host: American elm
FSVeg_Cat24_DeclineComplexesDiebacksWilts.docx