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The Missouri Department of Conservation advises homeowners to avoid pruning oak trees from mid-March through June. Pruning during this time can lead to oak wilt, an aggressive disease that can kill a healthy tree within months or years after initial infection.
If an oak tree must be pruned during this time, the fresh wounds should be sprayed or painted with tree wound dressing. This will protect exposed areas from insects carrying oak wilt spores. The dressing should be applied immediately to the wounded or storm-damaged area, as insects can be attracted to the fresh wound within minutes. Tree wound dressing is available for purchase at most local garden centers.
If a red oak tree is infected, the first sign of disease is brown, wilting leaves at the top of the tree within a few weeks, and the tree will die within one year. White oaks will also show signs of wilting leaves, however it may take years for the tree to die from infection.
For more information on oak wilt symptoms and prevention, visit the Missouri Department of Conservation website at https://short.mdc.mo.gov/ZTP.