Avoid oak wilt

With the early spring and warm weather in the area, many people are getting a head start on yard work. But those with oak trees should avoid trimming them to keep a deadly disease from spreading.

Oak wilt, fatal to the trees, is a concern earlier than normal this year due to the unseasonably warm weather. Typically the season to avoid oak tree trimming starts in April.

“But because of our early spring, I would not trim an oak tree right now,” said Tom Bakke with Red Wing public works.

Bakke likened the oak wilt disease to an infection, and the fungus that causes it to a foreign body in the tree.

“Its reaction to this is to completely shut off its capillary system,” he said. “It’s basically starving itself to death from nutrients and water.”

Red oaks are especially susceptible, though other varieties can be affected as well, Bakke said.

“White oaks have a better system,” he said. “A white oak might actually live through it, while a red oak doesn’t have a prayer.”

The disease typically starts at the top of the tree and works its way down. It is evident in signs such as the leaves turning brown at the tips, wilting and falling off.

There are two main ways the disease spreads. Certain beetles that feed on the tree sap can carry fungus spores from tree to tree as they start to awake and travel.

The other and more common way is underground. Oak tree roots tend to grow into one another and fuse, or graft, together. The disease can then move among trees through these “root grafts.”

“This is why this is such a devastating disease in the forest areas, because it can wipe out all the red oaks,” he said.

Avoid trimming trees to bring out the sap that attracts beetles.

Anything that opens the tree, from sawing branches to attaching a birdfeeder, can present a danger.

The beetles can infect the tree upon contact, Bakke said.

He suggested waiting at least until fall to trim trees, but said winter is best for any pruning, and not just for oaks.

If branches break off, such as during a storm, paint the open area with latex-based paint to seal it off, Bakke suggested.

Once a tree gets the oak wilt disease, there isn’t much to be done, he said. But to prevent the disease from moving on to other victims, people can break up the root grafts around the infected tree and farther out.

Using a spade or trencher deep underground to break up the roots will help stop the spread, Bakke said. Even if it is successful, do it again every few years to keep the roots from rejoining others, he added.

Oak wilt is present throughout Minnesota, including this area, Bakke said. Wisconsin officials also have warned the disease is a problem there as well.

The disease has been around for a while, Bakke said, so a lot of information is available. The Minnesota Department of Natural Resources and University of Minnesota, among others, have resources on oak wilt.

“It’s a very well-researched disease.”

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