Oak wilt is an incurable disease caused by a fungus that affects mainly live oaks and red oaks. The fungus clogs water-conducting tissues called xylem, which prevents water from reaching the leaves and causes the tree to wilt and die. Upon showing symptoms of yellowing or browning leaves, red oaks can die in as little as three to four weeks. Live oaks typically survive three to six months. Oak wilt has killed over 10,000 trees in the Austin area. This major loss jeopardizes the habitat of the golden-cheeked warbler, which relies on oak trees for foraging during the nesting season.
The disease can be spread either by insects or underground through interconnected tree roots. When sap-feeding beetles feed on the sweet-smelling fungal mats produced by infected red oaks, the spores stick to their bodies. The beetles can then transmit the spores from these infected trees to healthy live and red oaks by feeding on the sap oozing from fresh wounds. Live oaks generally grow in large, dense groups called mottes that have common, interconnected roots. This means that if one tree is infected, the disease can spread to the rest of the trees in the motte and create an infection center.
Although oak wilt cannot be cured, there are several suppression measures that can be taken to prevent the disease from spreading. To stop the underground spread of oak wilt, mechanical trenching is used to disrupt root connections between live oaks. Infected red oaks are cut down and either removed or allowed to dry out in order to avoid the formation of fungal mats. The fungal spores cannot survive when there is low moisture content in the wood. Oaks that are threatened with infection but are not yet showing symptoms can also be treated with a fungicide. For information about treatment of oak wilt, contact the Texas Forest Service or a local arborist. On a more general note, it is important to consider impacts on water quality when deciding to use chemicals such as pesticides or herbicides. Always use caution when applying chemical treatments and follow the provided directions carefully.
To prevent oak wilt at home, oaks should only be pruned during the summer and winter months when the beetles are least active. All wounds should be treated immediately with pruning paint. In addition, oak firewood should be handled cautiously as it can contain fungal mats and beetles. Avoid oak firewood from infected trees, and if possible, collect or obtain only wood that is dead or dry. To determine if wood is dry, look for cracks developing on the cut ends and loose bark. As an added precaution, cover any freshly-cut oak firewood with clear plastic and bury the ends. This dries out the wood faster to prevent a fungal mat from forming and also prevents beetles from either entering or leaving the woodpile. Black plastic should not be used because trapped beetles can find light holes to escape. For more information on the identification and management of oak wilt, visit the Oak Wilt Information Partnership.