AMES, Iowa — The recent warm weather has given a taste of spring, which means it’s time to finish pruning oak trees for the year 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, forest health program leader with the Iowa Department of Natural Resources. “However, the warm weather conditions indicate that spring might be a bit early this year and for that reason, we recommend finishing your oak pruning by the end of the second week in March.”
Oak wilt is caused by a fungus and has been present in Iowa for many years. It most commonly impacts red, black and pin oaks but can also infect white and bur oaks. If black, pin or red oaks are infected by the fungus, they usually die within the same summer they are infected. White oak and bur oak can often take a number of years before they succumb.
“A healthy tree can be infected by this fungus two different ways,” Feely said. “The first is through open wounds during the growing season, where the fungus is carried from a diseased tree to a healthy tree by a small beetle. The second 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 and the defoliation tends to start at the top.
“The best way to stop the spread of oak wilt is to prevent any wounding to oak trees during the growing season,” Feely said. “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 or sealants. Those products slow the tree’s ability to seal over the wound.”
More information on oak wilt prevention and control can be found on the USDA website. Contact Feeley at the Iowa Department of Natural Resources, 515-669-1402.