Question a da week

[Lee Borgersen]

                 Question of the week

Q: How do I spot oak wilt on my property, and what can I do about it?

A: Oak wilt is a difficult disease to diagnose. In northern red and northern pin oaks (leaf lobes with pointed tips), leaves wilt rapidly from the top and outer leaves down. The entire tree can wilt, lose its leaves and die in as little three to four weeks. Fallen leaves may be brown or partly green with a distinct line between brown and green. In white oaks (rounded leaf lobes), wilting happens one branch at a time, and the tree can take years to die. A pocket of trees with oak wilt will have dead trees in the center and dying trees surrounding it.

The oak wilt fungus is spread in two ways: below ground through interconnected roots to nearby oaks of the same kind, and above ground by sap beetles. The beetles are attracted by the fruity smell of fungus growing beneath the bark of diseased oaks. Beetles feed on the fungus, and fungal spores clinging to their bodies are carried to healthy trees recently wounded by storm damage or by pruning.

To avoid spreading oak wilt, don't prune oaks between April and mid-July, when sap beetles that spread the fungus are active. Trees that wilted during the growing season should be cut down in the winter and treated on-site or hauled to an approved wood waste site. To treat, you may remove the bark from the trunk or cut and stack to dry as firewood. If the diseased trees or firewood are not removed until the following spring, cover the stacked wood carefully with plastic tarp sealed at the ground to prevent beetles from getting to the wood.

Before you decide what to do, it's important to get an accurate diagnosis of the problem. Hire an experienced tree care professional, or send a sample to the University of Minnesota Plant Disease Clinic: https://pdc.umn.edu/.

Val Cervenka, DNR forest health program coordinator