Oak wilt is an incurable tree disease caused by a fungus, Ceratocystis fagacearum. It impairs the tree's ability to move water through its xylem and phloem. To understand how WCD staff manages oak wilt, it is important to know how it spreads.

This disease can infect all of our native oak species, though red oak and live oak trees are much more susceptible than white oaks. Among live oaks the disease often spreads via interconnected roots from an infected tree to adjacent healthy trees. Oak wilt does not spread as quickly through the roots of red oak trees but does spread in another way. In red oaks, spore-producing fungal mats form just below the outer bark layer and give off a distinctive odor that attracts insects, in particular sap-feeding beetles in the family Nitidulidae. These beetles can spread the disease by carrying spores from the mats directly to a fresh cut or wound on a healthy tree where they are attracted to the sap. People can also spread the disease by moving wood cut from infected trees to other areas, since fungal mats have been documented on logs, stumps and freshly cut firewood. If not disinfected, tools that have come in contact with sap from infected trees may transmit the disease when used to prune healthy trees.

To manage for the disease, staff follows recommendations from state agencies for preventing formation of new oak wilt infection centers and stopping the disease from spreading through root connections. BCP staff avoids cutting oaks from February to June, when fungal mats are most likely to form. Regardless of the time of year, all cuts on oak trees are immediately "painted" or sprayed using a tree coating material. It is essential to paint wounds just after they occur, since an unprotected wound will soon attract insects. Staff also disinfects all tools used on diseased trees after use.

In the Balcones Canyonlands Preserve, as well as areas of habitat outside BCP boundaries, this disease is especially serious because it kills off trees vital to survival by the golden-cheeked warbler, an endangered migratory bird that breeds in Central Texas in the spring and summer. Leafing out of the Spanish or Texas Red Oak, Quercus buckleyi, in early to mid, in early to mid March coincides with the arrival of these birds from their wintering grounds in Mexico and Central America. Caterpillars feeding on new leaves are in turn nourishment for warblers, at the beginning and throughout their nesting.

Staff biologists continually look for symptomatic trees while in the field. In summer 2007, the program will contract for helicopter time allowing biologists to fly over the City's BCP properties. They will look for clusters of dead live oak trees, as well as "flashing" diseased red oaks -trees whose leaves turn autumn colors that contrast with healthy green-leaved trees during the summer. These locations will be recorded with GPS equipment and later investigated from the ground.

Live oaks are continually monitored. Where it is warranted and equipment access is possible, staff may implement trenching. This strategy, though not 100% effective, is intended to disrupt root connections between diseased and healthy trees. Trees inside the trench in the direction of the disease center are also destroyed. Red oaks exhibiting symptoms of the disease are destroyed in a specific, purposeful, and time-intensive strategy. Trunk and limbs are sectioned into 12" to 16" logs and bark is stripped from large diameter logs (8"+), and the stump. This strategy accelerates the drying out and dying of the tree material to reduce moisture that permits formation of fungal mats.

For more information about oak wilt in Texas, visit www.texasoakwilt.org/.