Oak wilt, the devastating disease that has killed millions of oak trees in Central and West Texas counties, is infecting trees in the Dallas area, according to the Texas Forest Service. Making the situation worse, strong winds accompanying recent storms have wrenched limbs from trunks to create open wounds that can be infected by the fungus in an instant.
"It is definitely a major problem in the Dallas area," says Matt Grubisich, a regional urban forester with the Texas Forest Service, "with some sections worse than others. It's more of a problem in neighborhoods that have older, established live oaks and red oaks."
While any oak can get the disease, live oaks and red oaks (including Shumard, Spanish and blackjack oaks) are the most susceptible. White oaks (including post, bur and chinkapin oaks) are resistant to the fungus and rarely die from the disease. But oak wilt can kill a live oak within six to 12 months and a red oak in just four to eight weeks.
The culprit
Spores from the disease-causing fungus Ceratocystis fagacearum clog the tree's water-conducting system. A group of old oak trees will develop a common, interconnected root system, with one tree's roots grafting onto others' roots. Once one tree becomes infected, the spores can travel throughout the entire group of trees. If your neighborhood has been around for 30 to 60 years or more, you especially want to be familiar with oak wilt symptoms and realize that your oak trees are at great risk.
The carriers
Oak wilt also is spread through sap-feeding nitidulid beetles. The tiny beetles are attracted to fungal mats that can form underneath the bark of a red oak tree; the mats smell something like a rotten banana. The beetles feed on the mats, get covered inside and out with fungal spores, then fly off in search of other food.
Freshly wounded oak trees also have a sweet smell that attracts the beetles. Therefore, if a contaminated beetle feeds on a cut in a healthy oak tree, it can spread the fungus.
Mr. Grubisich can only theorize how the disease has spread to North Texas, but he suggests firewood transported to the city from other regions could be a cause. Should the fungus develop under the firewood's bark, the beetle is attracted to the smell of the fungus, feeds on it, then feeds on a pruning cut on an oak near the stack of firewood. That's how the disease could get a foothold in a neighborhood.
Because the beetles are most active and fungal mats are most likely to form in mild weather, the Texas Forest Service advises against pruning oak trees from February to June. The best times to prune, in terms of lowering the chances of oak wilt infection, are when the tree is not active: either in the dead of winter or during the hottest part of the summer. "Whenever you don't want to be outside is usually a good time to prune," says Mr. Grubisich.
In light of recent storm damage, where pruning wounds on trees are unavoidable, it is important to take extra precautions to prevent infection. There is no cure for oak wilt once it strikes.
Pruning paint
No matter when you prune an oak tree, immediately treat the cuts with a pruning paint. It only takes a few seconds for a tree to become infected, warns Mr. Grubisich. Do not go through a tree making all the necessary cuts, then come back and paint over the wounds. Make one cut, then paint over the cut area.
While it hasn't been proven that the disease can be spread through contaminated tools, Mr. Grubisich also suggests disinfecting pruners when moving from tree to tree. If an arborist comes to prune your trees, request that the tools be disinfected before trimming your trees. A mild bleach solution should suffice.
Halt the spread
In an oak wilt infection area, there are two techniques used to stop the spread of the disease, but they are difficult, costly and must be conducted by a professional. Arborists can sever the root connections between live oaks or a dense group of red oaks by trenching at least 4 feet deep and 100 feet beyond the perimeter of an infection center. Application of the fungicide propiconazole as a preventative can reduce oak wilt symptoms in live oaks. However, the fungicide does not stop the transmission of the fungus, and application must be timed carefully with the arrival of the disease.
"There is no silver bullet, no treatment for oak wilt," says Mr. Grubisich.
His best advice: Watch your neighbors' trees for signs of oak wilt to know whether your own trees are in danger. If you know oak wilt is in your area, he advises not planting live oaks or red oaks at all.
To help prevent new infections, try to burn all firewood by spring. If you cannot, do not store unseasoned firewood near healthy oak trees. In addition, you should cover it with clear plastic, burying the edges of the plastic. Cut and dispose of diseased red oaks immediately.Dallas Morning News
