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Time to Stop Pruning Oaks

  • 3/6/2018 12:18:00 PM
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It may still be cold outside, but it’s time to stop 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 oak tree between the end of March and the start of October,” said Tivon Feeley, coordinator for the Iowa Department of Natural Resources’ (DNR) forest health program.

However, Feeley said the warm weather conditions indicate that spring might be a bit early this year and for that reason, he suggests finishing oak pruning by this weekend.

Oak wilt is caused by a fungus and has been present in Iowa for many years. It mostly impacts red, black and pin oaks, but can infect white and bur oaks.  If black, pin, or red oaks are infected by the fungus, they usually die within the same summer. White oak and bur oak can often take years before they succumb.

“A healthy tree can be infected by the fungus through open wounds during the growing season that is carried from a diseased tree to a healthy tree by a small beetle,” Feeley said.  “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 that the roots of these trees are grafted and the fungus can move from the diseased tree to the healthy tree.”

Symptoms of infected trees usually include leaves turning a bronzed brown along the outer margins of the leaves. These leaves can often still have some green on them as they fall from the tree. The defoliation tends to start at the top of the tree. 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,” Feeley said. “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 can be found at