Pruning Oak Trees and Oak Wilt
Oak wilt is a serious fungal disease spread through root grafts
and picnic beetles. It can kill a red oak tree in as little as two weeks.
The white oak group can take several years to die. Wilting at the top of
the tree is one of the first symptoms. The outer portions of the leaves
turn dullish green-to-bronze-to-tan. The mid-vein and base of the leaf change
last.
A shared root system is the most common method of transmission of oak wilt. It can also be spread by picnic beetles that are attracted to fresh wounds on an oak tree. Do not prune oaks between April 15 and October 15 in the Twin Cities area. The fungus is producing spores at this time, and the picnic beetle is active; a deadly combination for the oak.
If an oak has been damaged and must be pruned during this period, make a clean cut and seal the area with a wound dressing. This, however, does not ensure that the tree will be protected against infection.
The ideal time to prune oaks is between November 15 and March 15. Wound dressings are not necessary at this time.
Revised: 03/10/98
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