Oak Wilt confirmed in Kalamazoo County
Kalamazoo, Mich.- Oak wilt is a lethal disease that can kill oak trees rather quickly. It has been confirmed in multiple locations in Kalamazoo County. The disease is most serious on members of the red oak family, including red oak, scarlet oak, black oak, pin oak, etc. Members of the white oak family are generally not nearly as susceptible: white oak, swamp white oak, burr oak, etc. The disease is potentially as serious as Dutch Elm Disease on American Elm.
Oak Wilt is caused by vascular wilt fungi that can be transmitted by insects or through root grafts. Symptoms in recently infected trees include: leaf margin browning progressing inward and from the leaf tips to the leaf bases; leaves on branches may appear to be wilting: some leaves may defoliate green or brown while others remain attached. These symptoms may be descriptive of other problems so diagnosis may be difficult.
Once a red oak becomes infected with the oak wilt fungus, it usually dies within several months. Because the oak wilt fungus becomes systemic within a tree, neighboring trees which happen to be root grafted to the diseased tree are also at risk. In this manner, the disease may affect many trees in an area.
Unfortunately, human activity is among the leading causes of infection. The health of oaks becomes high risk during the warm season months when they are injured through human practices, especially pruning, and through storm damage. Several species of picnic beetles are attracted to the fresh wounds caused by trimming and storm damage, and their activity transmits the fungus to healthy, recently pruned oaks from nearby diseased trees. Trees which come into contact with the fungus in the spring are often dead by August or September.
From Dr, David L. Roberts at MSU, “Anyone who prunes oaks during April, May and June is definitely taking some serious risks, even though such practices might have been acceptable previously.
Be suspicious of oak wilt if all or most of the following apply:
- Identity of the oak species as a member of the red oak family
- Presently, wilting symptoms are evident in live trees
- Sudden death, generally on the order of months
- Recent pruning or storm damage (months to a year)
- Proximity to other oaks (root graft transmission from nearby dead oaks)
- Elimination of other causes of oak death: gas leaks, root injury, other diseases, etc.”
There are several procedures to prevent oak wilt and to minimize its effects once detected. 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.
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).
If there is a possibility of root grafts, trenching at least 3-4 feet deep is recommended midway between the diseased and healthy trees to prevent transmission of the deadly fungus between diseased and healthy trees in close proximity.
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. Injection should not be attempted on an oak wilt-affected tree.
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