Between February 1 and June 30,sap beetles are attracted to fresh tree wounds and can transmit the oak wilt fungus to a healthy oak tree during pruning. The heat of July and August is believed to suppress the beetles and reduce the risk of infection. Note that all trees are under the normal stress of summer, depending on soil moisture, and some are still in their growing season then. So if you haven’t completed pruning of oaks by February 1, it’s best to wait until fall.
During the summer months, plan ahead for pruning your oak trees during the months of November through January, when the trees are growing very little, and the sap beetles are not active.
For more information, please see the library of reference material here:Tree Health