OAK WILT
By Bettie Burton
Oak Wilt is one of the most destructive tree diseases in the United States and
is killing oak trees in central Texas at epidemic proportions. There are areas
of Oak Wilt very near Cordillera, but as of Summer 2005 there was no presence of
it within the development. Oak Wilt is an infectious disease caused by the
fungus Ceratocystis fagacearum, which invades and disables the water-conducting
system in susceptible trees. All oaks are susceptible to Oak Wilt, but some
species are affected more than others. Red oaks, particularly Spanish oak,
Shumard oak and blackjack oak are extremely susceptible and may play a unique
role in the establishment of new oak wilt infections. White oaks, including post
oak, bur oak and chinkapin oak are resistant to the fungus and rarely die from
oak wilt. Live Oaks are the most seriously affected due to their tendency to
grow from root sprouts and form vast interconnected root systems that allow
spread of the fungus between adjacent trees.
SPREAD OF OAK WILT
Red oaks appear to play a key role in the establishment of new infection
centers. Fungal mats form beneath the bark of diseased red oaks. These mats
attract many insects, especially the sap-feeding nitidulid beetles. The fungus
may be transmitted by these small beetles as they emerge from the mats to feed
on FRESH WOUNDS on healthy oaks. Fungal mats can also develop on logs, stumps
and firewood cut from diseased red oaks.
IDENTIFICATION OF OAK WILT
Leaves on diseased live oaks often develop yellow veins that turn brown. Foliar
symptoms on live oaks and fungal mats on red oaks can be used as indicators of
oak wilt. A trained expert should be consulted for positive identification. Most
live oaks die over a 1-to 6-month period and red oaks within 3 to 4 weeks
following initial appearance of symptoms. During summer months diseased red oaks
can be spotted because of their bright autumn-like coloration in contrast to the
surrounding greenery.
DISEASE MANAGEMENT
There are currently three primary approaches used for oak wilt management in
Texas. The first approach attempts to prevent the new formation of oak wilt
infection centers by eliminating diseased red oaks by cutting and burning or
burying, handling firewood properly by buying firewood that has been dried for a
full year and covering with clear plastic and burying the edges, and by
ELIMINATING WOUNDS ON HEALTHY OAKS. The second approach involves trenching to
prevent the spread of oak wilt by interconnected tree roots. Finally, injections
of fungicide propiconazole (Alamo ™) into roots of individual, high-value trees
to help reduce crown loss and extend the life of the tree. This can be used as a
preventative treatment when oak wilt is present nearby and may have limited
success in trees with the earliest stages of infection. These measures will not
cure oak wilt but will significantly reduce tree loss.
*****PREVENTING NEW INFECTIONS*****
• Cut and dispose of diseased red oaks immediately.
• Avoid wounding oak trees, including pruning, from February 1 to July 1.
• This is the time the nitidulid beetle is most active.
• PAINT ALL WOUNDS AND FRESH STUMPS REGARDLESS OF SEASON.
• Handle oak firewood cautiously, burn all firewood before spring, and never
store unseasoned oak wood from infected trees near healthy oaks.
• Cover firewood with clear plastic, and bury the edges of the plastic.
• If you see anyone in Cordillera pruning oaks during the months of February 1
to July 1, or not painting pruning wounds in any season please notify Cordillera
management or an officer of the Cordillera Nature Club at once.
Information in this article is taken from the pamphlet "How to Identify and
Manage Oak Wilt in Texas" published by the USDA Forest Service and the Texas
Forest Service.