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Don't prune oak trees this spring
April through June is the high risk period for oak wilt
disease. And that means you should avoid pruning oak trees
until at least this July, say forestry specialists with the
University of Minnesota Extension Service and USDA Forest
If oak trees are accidentally wounded or pruning is
unavoidable, cover the tree wounds immediately-within minutes.
Use water-based paint or shellac.
Oak wilt is caused by a fungus, which is spread by both
root grafts and insects. It kills large numbers of oak trees
every year in Minnesota. In contrast to Dutch elm disease,
which has been very difficult to control, oak wilt can be more
November through March is the safe time for pruning oaks,
since the fungal pathogen and insect vectors are inactive.
July through October is the low-risk period.
A publication from the University of Minnesota Extension
Service titled "Oak Wilt in Minnesota" gives you
more details. You can view it on the Internet at http://www.cnr.umn.edu/FR/extension.
It's also available from county offices of the U of M
Extension Service. And for a nominal charge, you can order it
by calling (800) 876-8636 or (612) 624-4900 in the Twin Cities
area. Ask for item 3174.
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