February is prime time to prune oaks and reduce spread of oak wilt

February 13, 2020


February is a great time to manage and tend to oak trees. According to the Department of Natural Resources, the lowest risk of spreading deadly oak wilt is in winter.

The invasive fungal infection, which spreads naturally through either sap beetles or roots that have grown together, threatens all Minnesota oak species.

Waiting until spring to prune oak trees when the beetles are active, is a recipe to spread oak wilt, said Val Cervenka, DNR forest health program consultant.

“Wounding oak trees in spring and summer, when sap beetles are active, can attract spore-carrying beetles from infected trees and logs to fresh cuts,” Cervenka said.

Early detection and management are critical to preventing oak wilt’s progression into uninfected forests. As its name suggests, when oak trees suddenly lose all their leaves, notably in midsummer, that is a telltale sign of oak wilt. While the high-risk zone for oak wilt is currently east-central and southeastern Minnesota, Cervenka noted all oaks in the state are under threat from oak wilt.

To help stop the spread of oak wilt:

  • Prune oak trees now. Do not prune oak trees between April and July.
  • Cut down infected oaks now. Chip, debark, kiln-dry, or burn felled logs and large branches this winter (before April 1).
  • Leave firewood from infected trees in place. Tarp infected firewood from April through August and bury tarp edges to block beetles from reaching the oak wilt fungus. Make sure the tarp does not have any holes.

To learn more about detecting and managing oak wilt, visit the DNR’s oak wilt webpage.