Prevent oak wilt on trees by not trimming in spring

While the weather is warming up, April also brings a high risk for the often-fatal oak wilt disease across the state, and as a result, the DNR recommends not pruning or cutting oak trees from April through July. Oak wilt is widespread in southern Wisconsin, but it is still a new and uncommon disease in much of northern Wisconsin.

As spring draws property owners outdoors to start seasonal yard maintenance and cleanup projects, when it comes to the health of oaks trees, refraining from taking the chainsaw or trimmers to the trees, goes a long way to ensure they stay healthy for many more spring seasons to come.

Pruning/cutting oaks in spring and early summer, leaves them vulnerable to oak wilt, which rapidly kills trees in the red oak group and weakens those in the white oak group. Any damage during this time, including broken branches caused by storms, exposes living tree tissue beneath the bark and provides an opportunity for the oak wilt fungus to attack the tree.

Tree paint or wound dressing is not normally recommended on pruned surfaces, but for damaged oaks, a light application of these products immediately, if possible within 15 minutes, may be the only defense against oak wilt infection from April through July. Wounds are not susceptible to oak wilt after 72 hours.

Oak wilt spreads over land, by sap-feeding beetles that carry the fungal spores from infected oaks to fresh wounds on healthy oaks, and underground, from infected oaks to nearby healthy oaks through grafted or interconnected, root systems.

Red, black and pin oaks are highly susceptible to oak wilt. Once infected, they can die within a few weeks. White and bur oaks are much less susceptible. If infected, they can take months or years to die, or they may even recover.

Avoiding tree pruning in spring not only protects trees from disease, but also helps trees regenerate. Check with the local municipality to find out if they have their own oak wilt ordinances that should be followed, as well.

Oak wilt and other diseases move easily on, or in, firewood logs year-round, so keeping firewood local or purchasing Wisconsincertifi ed firewood, is another critical component of protecting trees and maintaining healthy forests.