Oak wilt is a fungal disease affecting oak trees. It is caused by the fungus Ceratocystis fegacearum. The symptoms vary from species to species, but generally include wilt, discoloration, defoliation, and eventually death. Oak wilt it affects all species of oak found in the northeastern United States. Its fungus spreads from a diseased tree to a healthy tree either through connections between tree roots or insects.
What species are most affected?Oaks in North America are generally categorized under two main groups (based largely upon porosity and leaf shape): white and red oaks. White oaks have a characteristic rounded leaf edge and red oaks have pointed leaf edges and larger unclogged pores. Due to this difference in porosity, the red oak family is most susceptible to the fungus and the trees die faster than the white oak group trees.
Northern red and pin oaks are particularly vulnerable. They can die within two months of infection. White oaks are much more resistant and can live for years with infection. Other trees in the white oak family – such as swamp white, and bur – are somewhat less susceptible and may live for several years with infection, losing one or two branches each season usually from the top down.
How does oak wilt spread?
Oak wilt fungus spreads through two main methods: the transfer of spores from infected to healthy trees by insects, and movement of the fungus from a healthy tree to an infected tree through root grafts.
Sap-feeding beetles carry the fungus on their bodies and transfer it to healthy trees when they feed on an open wound, leaving the spores to cause infection.
Oak wilt symptoms and management
An infected tree wilts from the top down, one branch at a time. The rate of wilting depends on species. Prevention is necessary as there is no permanent cure. To prevent beetle transmission, pruning should be avoided in the spring months.
Care should be taken to minimize risk of injury, especially from construction. In the case of injury (either from a storm or accident), tree paint can be used to protect the wound. Root graft disruption is another method of preventing infection. It can be done using a vibrating plow with a long, narrow blade.
Dead trees should be removed before April, but only after root grafts have been successfully disputed.