In the wake of recent severe storms in Canfield, Boardman and elsewhere, homeowners are busy clearing debris and assessing broken branches. However, university researchers warn that for oak trees, the most significant danger may not have been the wind itself, but a silent, fungal killer waiting for an invitation.

Oak wilt, caused by the fungus Bretziella fagacearum, is a devastating disease that clogs a tree’s vascular system. Once infected, the tree’s water-conducting vessels — the xylem — become blocked by fungal mycelium and the tree’s own defensive structures called tyloses. This prevents water and nutrients from reaching the leaves, leading to rapid wilting and, in many cases, total tree death within a single season.

Oak wilt infects all oak trees, but the red oak group (pin, black, northern red) are highly susceptible. The entire tree can lose its leaves and die within just two to six weeks.

The white oak group (white, bur, swamp white) are more resilient. White oaks may take one or several years to die or may survive longer.

The link between storm damage and oak wilt is a matter of timing. The disease spreads “overland” primarily through sap-feeding Nitidulid beetles, often called sap beetles.

These insects are attracted to the sweet-smelling fungal mats that grow under the bark of infected red oaks. The beetle picks up the fungal spores from the infected tree. When a storm tears a branch or injures a healthy tree, it creates a wound that leaks fresh sap, attracting the beetle.

According to the Ohio State University and Texas A&M Forest Service, these beetles can arrive at a fresh wound in as little as five minutes.

If a beetle carrying fungal spores visits a storm-shattered oak during the high-risk season — typically April through mid-July — it can inadvertently transplant the disease.

Once established in a new tree, oak wilt becomes even harder to manage. Experts at Purdue and Michigan State University note that up to 90% of new infections occur underground through root grafts.

When oak trees grow near one another, their roots can fuse, creating a shared biological highway. The fungus travels through these grafts to neighboring trees, resulting in an outwardly expanding “disease center” of infected oaks.

Homeowners are the first line of defense. University extension specialists recommend the following cultural practices:

● Mind the calendar: Avoid all oak tree pruning during the high-risk window of April 15 to July 15. For zero-risk management, some arborists suggest avoiding pruning until after the first hard frost.

● Seal wounds immediately: If you must prune an oak or a storm causes damage, you must act within minutes or hours to protect the tree. Immediately paint the fresh cut or wound with latex-based paint or a commercial pruning sealer to hide the scent of sap from beetles. But painting and sealing are not always possible, particularly immediately after a major storm.

What can be done now?

Watch for symptoms of oak wilt. Watch for rapid leaf drop and discoloration before the fall season, especially in red oaks. If you see these symptoms, it doesn’t mean your tree has the disease, but it’s recommended you send a sample of the tree to a university lab for testing. The Mahoning County OSU Extension Office has information on contacting plant disease testing laboratories.

Oak wilt was first identified in the United States in 1944.

The combination of public awareness of the disease and taking appropriate university-recommended actions can help control this disease.