The Iowa Department of Natural Resources (DNR) recommends pruning oak trees between November 1 and mid-March. This is the preferred time for routine oak pruning because oak trees are usually dormant and the insects that can spread oak wilt are less active.
“November 1 through mid-March is a good statewide window for pruning oak trees,” explains Tivon Feeley, Forest Health Program Leader with the Iowa DNR. “These dates are a guide since weather conditions vary from year to year and across the state.”
Oak wilt risk does not begin or end on the same date everywhere in Iowa. Northern Iowa may cool down and trees may enter dormancy before southern Iowa, while unusually warm fall or spring weather can extend periods of risk.
Because warm fall weather has continued in parts of Iowa this year, the DNR recommends waiting until November 1 for routine oak pruning. Landowners, arborists, foresters and loggers considering oak work outside the preferred winter window should check current Iowa DNR guidance or contact DNR forestry staff.
“We look at local conditions, including temperatures, whether oak trees have gone dormant and if the insects that can spread oak wilt are still active,” Feeley said. “That is especially important near the start and end of the winter pruning season.”
Oak wilt is a serious disease of oak trees. It can spread when small beetles carry the oak wilt fungus from an infected tree to a fresh wound on a healthy oak. It can also spread underground through roots that connect nearby oak trees.
Red, black and pin oaks are especially susceptible and can die within the same growing season after infection. White and bur oaks can also become infected, but often decline more slowly.
If an oak tree is damaged by a storm or must be pruned when oak wilt risk is present, immediately cover the fresh wound with latex or acrylic paint to help prevent beetles from reaching the cut. Wound paint is not needed for normal pruning during the preferred winter season.
Learn more about oak wilt prevention and control at www.iowadnr.gov/oakwilt.