What is oak wilt?

Oak wilt results from infection by the fungus Ceratocystis fagacearum, which invades the water-conducting tissues of oak trees and triggers a defensive response that ultimately starves the tree of moisture and nutrients. Infected oaks can decline rapidly, particularly red oaks, which may die within a single growing season after symptom onset.

The disease spreads through two primary routes in Westchester County and the Northeast. Root grafts allow the fungus to travel between adjacent oaks whose root systems have naturally fused underground, creating a direct pathway for infection. The fungus also spreads when oak bark beetles (particularly Xyleborinus saxesenii) feed on infected trees, pick up spores on their bodies, and fly to healthy oaks, where they bore into the bark and inoculate new hosts.

Because beetles are most active in spring and early summer, municipalities and arborists enforce strict timing restrictions on oak pruning and tree work. Fresh pruning wounds attract beetles seeking food and breeding sites. In Westchester County and much of the Northeast, oak pruning is typically prohibited from April through July. This restriction prevents creating attractive entry points for beetle vectors when pest populations are at their peak.

If oak wilt is suspected on your property, contact a certified arborist or tree health specialist immediately. Early diagnosis and proper management, including root barrier installation or tree removal, can prevent spread to neighboring oaks.