|
Identification Of Oak Wilt
Foliar symptoms, patterns of tree mortality and the presence of
fungal mats can be used as indicator of Oak Wilt. However, isolation of the fungus in the laboratory may be required to confirm the diagnosis. A trained experts should be consulted when in doubt.
Patterns of Tree Mortality
Most Live Oaks defoliate and die over a 2 to 6 month period
following the appearance of symptoms. Some Live Oaks may take longer to die, and a few untreated trees may survive many years in various stages of decline. A few Live Oaks in Oak Wilt centers escape infection or may be resistant to the fungus and will remain unaffected by the disease.
Red Oaks seldom survive Oak Wilt and often die within 3 to 4
weeks, after the initial appearance of symptoms. During summer months, diseased red oaks often can be spotted from a distance because of their bright Autumn-like coloration in contrast to the surrounding greenery.
Foliar Symptoms
Leaves on trees often develop chlorotic (Yellow) Veins that
eventually turn necrotic (Brown), a symptom called veinal necrosis (fig. 1). Defoliation may be rapid, and dead leaves with brown veins, often can be found under the tree ( fig. 2) for months after defoliation. Leaves may exhibit other patterns of chlorosis and necrosis, such as interveinal chlorosis, marginal scorch, or tip burn, but these symptoms are less reliable than veinal necrosis for diagnosing oak wilt in live oaks.
Foliar symptoms of oak wilt on red oaks are less distinct. In early
spring, young leaves simply wilt, turning pale green and then brown. Mature leaves develop dark-green, water soaking symptoms or turn pale green or bronze, starting at the leaf margins and progressing inward. |
|
fig. 1
click for more detail
|
|
fig. 2
|
