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