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Oak wilt is one of the most destructive tree diseases in the United States. The disease has killed more than 1 million trees in 76 Central Texas counties. Oak wilt is an infectious vascular disease caused by the fungus Bretziella fagacearum. The fungus invades and disables the water conducting system in susceptible trees. All oaks can be infected with oak wilt, but some species of oak are more susceptible than others. Red oaks, particularly Spanish oak (Quercus buckleyi), are very susceptible to the fungus. White oaks, like post oak (Q. stellata) and bur oak (Q. macrocarpa), are resistant to the fungus and rarely die from the disease. Live oaks (Q. virginiana and Q. fusiformis) are intermediate in susceptibility to oak wilt. However, they are seriously impacted by the disease because of their tendency to form root sprouts that result in a vast interconnected root system allowing the disease to easily spread to adjacent trees.
ALL OAKS CAN BE INFECTED BY THE FUNGUS THAT CAUSES OAK WILT!
Oak trees in central Texas are placed into one of two groups – red oaks or white oaks. Red oaks are the most susceptible to oak wilt, will typically die within two to four weeks of symptom appearance, and can play a unique role in spreading the disease. Common red oaks in central Texas include: Spanish oak (Quercus buckleyi), Shumard oak (Q. shumardii), and blackjack oak (Q. marilandica).
Oaks in the white oak group are the most resistant of the disease, with variations among the group depending on species. Post oak (Q. stellata), bur oak (Q. marilandica), and Mexican white oak (Q. polymorpha) are very resistant of the disease. These species may exhibit some canopy loss, but rarely die when infected. White shin oak (Q. sinuata var. breviloba), chinquapin oak (Q. muehlenbergii), and Lacey oak (Q. laceyi) can grow in stands with interconnected root systems, enabling the fungus to infect adjacent trees. These species are more resistant of the disease than red or live oaks and usually survive infection with moderate to severe canopy loss, but they can die in large numbers from the disease.
Live oak (Q. fusiformis) is a member of the white oak group and is the most common and abundant oak in central Texas. While live oaks succumb to oak wilt in the greatest numbers, they are intermediate in susceptibility to the disease with a small percentage (< 20%) surviving infection. Live oaks share a common root system. All live oaks in a stand are likely connected to each other and other live oaks as far as 200 feet away. If oak wilt infects one of the trees in the stand, the disease spreads through the common root system to adjacent trees and an oak wilt infection center begins.
Oak wilt spreads to other oak trees in two ways – long distances with the aid of certain beetles or locally through common or grafted roots. Sap-feeding (nitidulid) beetles are believed to be responsible for much of the long distance spread of oak wilt. During the spring, the oak wilt fungus forms special spore-producing structures called fungal mats on red oaks. Nitidulid beetles are small (about 1/8-inch long) and are attracted to oak wilt fungal mats because the mats have a sweet, “fruity” smell. Mats form underneath the bark of diseased red oaks and are not known to occur on live oak trees. The fungal mats apply pressure under the bark causing a tiny crack to form.
Prevention plays an important role in the management of oak wilt. Landowners and homeowners can take an active role in oak wilt prevention by taking the following steps:
Yes, the City has experienced cases of oak wilt within City limits.
The City created a program to partially reimburse homeowners with oak wilt abatement expenses.
The City is encouraging residents to donate to the Oak Wilt Fund at First United Bank to help residents offset some of the oak wilt abatement costs. If oak wilt spreads throughout the City, it will affect our beautiful trees and property values.
There are education materials on the City website and at City Hall to help with identifying oak wilt and some precautions you can take to avoid oak wilt damage.
More about the Oak Wilt in Texas and the Texas Oak Wilt Suppression Project: