Oak Wilt

Oak wilt is a fungal disease affecting oak trees. The fungus grows and spreads throughout the tree’s vascular system, depriving the host of nutrients and water. The presence of the pathogen triggers an immune response from the host tree which further blocks the movement of water. These two symptoms effectively choke the oak tree until it begins to wilt and die.

How is Oak Wilt Transmitted?

The fungus responsible for oak wilt—Bretziella fagacearum—is primarily spread in two ways. First, oak wilt may be transmitted over long distances by sap-feeding beetles, commonly known as picnic beetles. These beetles feed on the spore mats of diseased oak trees. The beetles then carry the spores with them to feed on the sap from a fresh tree wound, such as a pruning cut.

Second, oak wilt may be transmitted by root grafting. When two trees of the same species grow in close proximity to one another, their roots will graft together and fuse, much like a skin graft. If either tree is infected, the pathogen may spread to the other. This is why oak wilt is a problem if it is present in your neighborhood.

Preventing Oak Wilt

The most important step to prevent oak wilt is to avoid wounding your oak tree when conditions are favorable for transmission. According to the Texas Forest Service, you should avoid pruning oak trees from February 1 to June 30. If it is necessary to prune or otherwise wound an oak tree in that time, a pruning sealer should immediately be applied to the wound.

If oak wilt has been identified in your neighborhood, preventative oak wilt injections may protect your oak trees from the disease. The fungicide spreads throughout the vascular system of the tree, preventing the pathogen from taking root. The Texas Forest Service recommends injecting high-value oak trees that are within 75–100 ft. of a symptomatic host tree.

Susceptibility to the disease varies by species. While white oaks are generally resistant to oak wilt, red oaks are very susceptible to the disease and may die within months or even weeks of infection. Live oaks lie somewhere in the middle: some die within a few months, others die in 1–2 years, and a few (about 1/10) are infected but never succumb to the disease.

Treating Oak Wilt

If your oak tree becomes infected, it is possible to perform therapeutic injections. This involves injecting the symptomatic tree with fungicide to slow and hopefully stop the development of oak wilt in that tree. The best results are achieved if no more than 30% of the canopy is showing symptoms of oak wilt. If more than 30% of the canopy is symptomatic, it is unlikely that therapeutic injections will be effective.