Oak Wilt

For further information contact University of MN Master Gardner Coordinator at 763-689-8254

How Infection Occurs

Oak Wilt is the name of a fungus and a disease. There are two ways oaks can get infected with Oak Wilt:


The fungus is carried by the picnic beetle to a fresh wound on a healthy oak between mid-April and early-July. The tree is now infected.


After that first oak dies, other oaks of the same group - connected via root grafts - will be infected. This is what an "Infection Center" is. Rarely will a red oak join with a white oak and form root grafts. The Infection Center grows outward, compounding oak mortality every year. Unless stopped, the problem gets worse.

Every year, the majority of oaks die from root graft spread, not overland spread, of oakwilt disease.

Important Things to Remember about Oak


  • Remember - Healthy oaks wounded between April 15 and July 1 will get infected with oak wilt.
  • Managing this disease means understanding it and knowing when to do and not do certain things.
  • Threat of infection via airborne spread happens April 15 to July 1.
  • Threat of infection via root graft (underground) spread happens throughout the year and is visible from leaf-out in May to leaf drop/autumn color in late September early October.
  • White oaks are not more resistant to oak wilt. White oaks get infected just as easily as reds; but once infected, white oaks take much longer to die (1 to 5 years as opposed to 2 to 4 weeks for a red oak).
  • Although the fungus is a cousin of Dutch Elm Disease (DED), oak wilt is not the same as DED. Oak wilt is easier to control that DED.


  • If plowing is followed up with CTL (cut to the line), then the plowing is 85% effective.
  • The deeper the blade, the more success you'll have in breaking root grafts.

Tree Processing

  • High priority is to cut the recently diseased and healthy oaks in the "Zone" on the diseased side of the plowline.
  • Remember - By cutting down a dead oak or any other tree species among healthy oaks between April 15 and July 1 will infect those healthy oaks.
Before and after of area infected with Oak Wilt and the infected trees later cleared off