Oak Wilt is a Fungus
Oak Wilt is a lethal vascular disease that is caused by the fungus
Ceratocystis fagacearum. The fungus lives and grows in the
current year’s xylem and all families of oaks are susceptible.
This disease is often misdiagnosed.
Oaks attempt to stop the spread of the fungus by producing gummy
substances called tyloses. The combination of the fungus and tyloses
disrupts the flow of water to the canopy and contributes to the
leaf wilting and drop associated with oak wilt.
Diagnosing Oak Wilt Diagnosing oak wilt begins with
observing foliar symptoms, patterns of tree mortality, and the presence
of fungal mats. Foliar symptoms are a great indicator, but are only
present during certain times of the year. Patterns of tree mortality
can be viewed any time of the year and will give a good indication
of disease presence. A good way of diagnosing oak wilt is to look
around first. If you see odd patterns of tree loss in an area, you
may find the progression of oak wilt. Fungal mats form on red oaks
in the spring and are great indicators when found. The fungus produces
pressure pads between the bark and the wood, which cracks the bark
open and emits a fruity odor.
Leaf Symptoms Leaf symptoms on live oaks are
easily noticeable. Leaves will develop a yellowing and eventual
browning of the veins, which is called veinal necrosis. Red oaks
will often turn pale green and then brown. It is common to find
partially dying leaves, of both live oaks and red oaks,
lying underneath a tree. Unlike live oak symptoms, on red
and white oak the symptoms progress from the outside margins
to the inner leaf.
Sapwood streaking beneath the bark is a diagnostic indicator
of infection in the red oak and white oak families.
This brownish discoloration may not always be apparent, however,
but even if it is not seen, oak wilt may still be present.
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| Leaf
symptoms of Oak Wilt on live oak |
Red
Oak dying from Oak Wilt |
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