Foresters Corner
When is a good time to prune trees? The rule of thumb for most amateur arborists is to prune your tree after the
leaves have fallen in the fall and before the buds have broken open in the spring. Pruning this time of year minimizes
the chance for infection of the newly created wounds. It is not a good idea to prune any tree in spring or summer, but
especially oak.
Pruning Oak in the summer makes it vulnerable to infection by the fungus that causes Oak Wilt. Oak wilt kills oak
trees. The fungus kills the tree by girdling. It spreads between the bark and stem and into the conducting tissue of
the tree blocking the flow of water and nutrients. The fungus is introduced to the tree on wounds when beetles
carrying the fungus on their bodies are attracted to the smell produced by oak trees wounded in the late spring and
early summer months.
Oak wilt has some symptoms that can be fairly easily identified. One symptom is the shedding of leaves in the middle
of the summer that appear to be half dead. If the leaves of an oak tree appear half dead, (wilted) it is a good sign that
there is something wrong with the tree. Look for wilted leaves in late June or early July and leaf shedding shortly
after.
Unfortunately, there are no known cures for Oak Wilt. There are only control and prevention measures. Controlling
of an Oak Wilt infection center requires breaking the root grafts between the trees using a six-foot vibratory plow and
destroying all of the oak material from the affected area. The root grafts need to be severed because the wilt fungus
uses these grafts to spread to other trees.
In order to prevent the introduction of Oak wilt onto the Ranch, the forestry committee
adopted a policy of not allowing thinning in oak stands after April 15 th . This minimizes the
chances of any wounded trees becoming infected. There are some measures Ranch member
can take to prevent the introduction of Oak Wilt. Do not prune oak while the leaves are on
or after April 15 th . Do not bring firewood from other areas onto the Ranch. Firewood from
other areas may carry Oak Wilt or other devastating insects or diseases. Most of this article
is synthesized from “How to identify, prevent, and control oak wilt” (available on the internet
at https://www.fs.usda.gov/naspf/publications/how-identify-prevent-and-control-oak-wilt).
Submitted by,
Terry Manty, ACF, CF & Gerald Grossman, ACF, CF, Grossman Forestry
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