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Time to stop pruning oaks

March 5, 2017
Kevin Williams - Grundy County Conservation Director , Reinbeck Courier

A short time back in the news columns, I wrote on tree trimming. I received a news release from the Iowa Department of Natural Resources that I wanted to pass along to you on that timely topic. This has to do specifically as it relates to trimming oaks. Our department has planted several oak plantations in various county parks and wildlife areas over the years. The two areas that contain native bur oak stands are Wolf Creek Recreation Area and the Wolfe Family Preserve.

Recent warm weather conditions indicate spring might be a bit early this year, and for that reason, the Department of Natural Resources suggests finishing oak pruning by March 15.

"The best way to prevent the spread of oak wilt is to not prune any oak tree during its growing season," says Tivon Feeley, DNR forest health program leader. "This is generally between the end of March and the start of October; however, this year, the growing season may be getting a head start."

Oak wilt, which is caused by a fungus, has been present in Iowa for many years. The Iowa trees most commonly impacted by this disease are species such as red, black and pin oak, but it can also infect white and bur oak.

According to Feeley, if black, pin or red oaks are infected by the fungus that causes this disease, they usually die within the same summer. 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 this disease 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 are grafted and the fungus can move from the diseased tree to the healthy tree.

Symptoms to look for on infected trees usually include leaves turning a bronzed brown along the outer edges. These leaves often still have some green on them as they fall from the tree. And another symptom is defoliation starting 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 use pruning paints/sealants, as these products slow the tree's ability to seal over the wound.

More information on oak wilt prevention and control can be found at:



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