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Time to Stop Pruning Oaks

  • 3/8/2016 6:33:00 AM
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Spring weather seems to be here a bit early this year and according to the Department of Natural Resources, that means it’s time to finish pruning oak trees to prevent the spread of oak wilt. 

The best way to prevent the spread of oak wilt is to not prune any oaks between the end of March and the beginning of October.  However, with the recent warm weather conditions, property owners should finish pruning oaks by the middle of March.

“Oak wilt, which is caused by a fungus, has been present in Iowa for many years,” says Tivon Feeley, DNR forest health program leader. “The Iowa tree species most commonly impacted by this disease are red, black and pin oaks, but it can also infect white and bur oaks.” 

According to Feeley, if black, pin or red oaks are infected by the fungus, they usually die within the same summer they contract the disease. White oaks and bur oaks can often take a number of years before they succumb to the disease.

A healthy tree can be infected by the fungus that causes oak wilt in two different ways. The first is through open wounds during the growing season, when the fungus is carried by a small beetle from a diseased tree to a healthy tree with an open wound.

The second form of infection is through root grafts between oak trees of the same species.

“For example, if a red oak is infected and there is another red oak within 50 to 100 feet there is a good chance the roots of these trees have grown together or are grafted, and the fungus can move from the diseased tree to the healthy tree,” said Feeley.

The primary symptom to look for on infected trees is leaves turning a bronzed brown. These leaves often still have some green on them as they fall from the tree and leaf loss tends to start at the top of the tree. 

According to Feeley, the best way to prevent the spread of oak wilt is to prevent any wounding to oak trees during the growing season. If a tree is wounded from storm damage or pruning is required during the growing season, treat the wounds immediately with a wound dressing such as acrylic paint.  Do not purchase pruning paints/sealants.  Those products slow the tree’s ability to seal over the wound.

More information on oak wilt prevention and control from the U.S. Forest Service can be found at