THE TREE DOCTOR (aka The Plant Doctor)

Management of Oak Wilt

There are several procedures to prevent oak wilt and to minimize the effects of oak once detected. Clearly, the first one is to prevent oak wilt from becoming established in your oaks. Once oak wilt is detected, or perhaps even strongly suspected, several important steps need to be followed. Some of these steps depend on the value of the trees and the extent that the plant owner may want to invest in their oak trees.

1) Pruning:  DO NOT PRUNE during the warm season; trimming is a major cause of oak wilt infections in Michigan today. If oaks need to be pruned, the dormant period is best - November through February. If storm damage occurs during the warm season, clean-prune the branch 1-2 feet below any visible injury and seal with a pruning paint. Repair of storm damage should occur as quickly as possible-optimally within hours or within a couple of days of the damage.

Storm damage which has occurred during the dormant (winter) months is not of particular concern for oak wilt. Nevertheless, winter storm damage should be repaired during the winter months and not during the warm season. It is not advised to use pruning paints during winter storm repair.

Except for emergency situations, cessation of pruning during the warm season, is probably our most effective tool for preventing oak wilt at this time. Compared to Dutch Elm Disease, in which elm bark beetles can easily transmit the fungus from diseased trees to healthy trees, the oak wilt insect vector is inefficient at transmitting the oak wilt fungus when no wounds on oaks are present.

2) Removal:  Infected trees should be removed promptly. Once a tree has become infected, there is little chance to save it. Tree removal should take into account disposal. Wood may be used for firewood provided it is debarked or covered and sealed during the spring/summer months (remember-diseased trees with bark serve as a source of further infection for neighboring trees). In some situations of dense stands of trees, a tier of healthy oaks surrounding an oak wilt-affected tree may need to be sacrificed to “save the forest”. Remember to trench before removal if other oaks are nearby and there is a possibility of root grafts between trees (see below).

3) Trenching:  If there is a possibility of root grafts, trenching at least 3-4 feet deep is recommended midway between the diseased and healthy trees. This effort will hopefully prevent transmission of the deadly fungus between diseased and healthy trees which may be root grafted if in close proximity.

4) Injection:  Micro- and macro-injection of fungicides is a protective measure against infection. It should be understood that injection may be expensive and is often not a guarantee of tree survival. In a landscape or  urban situation, injection of  apparently healthy” oaks in the vicinity of dying oaks might be a recommended practice if economics condone the treatments. Injection should not be attempted on an oak wilt-affected tree except as a last ditch, fruitless effort. Research has generally shown that once oaks become infected with the oak wilt fungus, there is little that can be done to save the infected trees. Hence, efforts should be directed toward saving non-infected trees.

5) Vigilance:  Because of the size, grandeur and value of our oak trees, a constant vigilance must be maintained about the threat of oak wilt. If any unusual problems or symptoms are associated with oaks, obtain help. It is imperative that we spread the words- “DO NOT PRUNE!” during the warm season. Storm damage should be assessed and repaired promptly. It is highly recommended that community efforts be established to thwart the threat of oak wilt. Any time an oak tree succumbs to oak wilt in a community, it eventually becomes everyone’s problem.