How Does Oak Wilt Spread?

Identification

• Oak wilt is caused by the fungus Ceratocystis fagacearum and attacks members of the Quercus family. According to the U.S. Department of Agriculture, no species of oak tree are resistant to this disease, but red oak is most commonly infected. White oak is infected least often and suffers less damage than other members of the oak family. Once trees are infected with oak wilt, there is no way to save them. Avoiding the spread of disease and removing infected trees that become weak are the only ways to manage oak wilt.

Effects

• Oak trees infected with oak wilt may exhibit symptoms similar in all species. Most oak trees with oak wilt have leaves that turn dull green, appear water-soaked and turn brown. Infected leaves eventually wilt and leaves may curl. Oak wilt spreads rapidly, with only white oak trees dying slowly from the disease. All other species of oaks die soon after infection. Fungus mats may be visible on the bark of infected trees; these mats cause the bark to crack and encourage infestations of bark beetles. These beetles are one way oak wilt fungus is spread to other trees.

Insect Vectors

• When bark beetles and sap-feeding beetles feed on infected oak trees, they help spread the disease to other trees in close proximity. Fungus mats emit a fruity scent that attracts beetles to trees from long distances. During feeding, fungal spores attach themselves to beetles' bodies, where they are carried to other trees and enter trees through wounds on the bark. Wounds are usually caused by pruning, storms or other insects.

Root System

• When oak trees growing near trees infected with oak wilt, the disease may be spread through connected root systems. This is known as "local spread," which is characterized by the rapid spread of oak wilt fungus through root systems, causing many trees to become infected and create a center of infection. According to the USDA, Texas live oak and northern pin oak often share root systems spread throughout many trees.