THE TREE DOCTOR (aka The Plant Doctor)

Oak Wilt: White Oak Species

White Oak bark
White Oak bark

We know that oak wilt is quickly lethal to members of the red oak family, but what about white oaks? Like the red oak family (pointed leaf lobes), the white oak family (rounded leaf lobes) is comprised of a rather generically diverse genus of trees. Burr, Swamp white and White oaks among others, are common species found in Michigan. So, how do we manage white oaks? Is it OK to prune them during the summer?  My advice: treat them with the same caution and respect that professionals give red oaks. Do Not Prune White Oaks during the warm season! 

 Review suggested article: Advantages of Winter Pruning

Scientists disagree to some extent on the severity of oak wilt on members of the white oak family.  Some say they've not witnessed a white oak killed by oak wilt, some say white oaks are infected but die slowly, and some say white oaks may be infected and subsequently recover. From my perspective, white oaks can become infected. Some may die and some may live as stressed trees to later decline from other causes. Many white oaks die in Michigan each year. I'm suspicious that the large number of white oak deaths, commonly attributed to two-lined chestnut borer and "oak decline" and perhaps other reasons, may actually on occasion, if not frequently, be caused by the oak wilt fungus. 

Concern for oak wilt in a white/red mixed stand of oaks may be warranted. It is well documented that the oak wilt fungus may be translocated through grafted root systems. I suspect that the number of root grafts between members of reds and whites is rare if not non-existent compared to the grafts occurring intra-family/species. Nevertheless, white oaks could potentially harbor the lethal fungus as  "Typhoid Mary" trees for infection of nearby red oaks or white oaks through alternative means such as insect transmission.

 Red oaks, for all practical purposes, are doomed when fungal contact is made to wounds or other modes of entry. And, injections are generally a wasted effort on these infected red oaks. The good news about oak wilt and white oaks: white oaks tend to respond to fungicide injection treatments and may recover with time. If oak wilt is suspected in members of the white oak family, it may be advisable to determine whether they respond to fungicide injections.... at least on a trial basis. Prophylactic treatment of valuable, high profile white oaks may also be justified in certain situations. 

Oak Wilt Research

If individuals or organizations wish to contribute to our oak wilt research, they may do so by contacting me at Michigan State University Extension at this address:

Oak Wilt Research, c/o Dr. David L. Roberts, Ph.D., Senior Academic Specialist
Michigan State University
College of Agriculture and Natural Resources

173 Giltner Hall, East Lansing, MI  48824-1101
Cell Ph: (248) 320-7124 preferred
Lab Ph: (517) 355-4518