Simply Science: Oak Wilt

2:46 PM, Oct 1, 2012   |    comments
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HINKLEY, Minn. - Trees across the state are turning brilliant shades of red, orange and yellow. But some oaks are already bare.

Oak Wilt Disease is a fungus that does just what its name suggests. Once infected, Oak trees wilt from the top to the bottom until they die.

From Saint Croix State Park near Hinckley, DNR Forester, Ryan Blaedow says, "The tree in response tries to plug up its vascular system to keep that fungus from spreading. And when the tree plugs up those vessels, it may stop the fungus from spreading but it also prevents water from throughout the tree."

No Water means the tree wilts.

City Forester Emily Ball is also seeing infected trees in Minnetonka.  She adds, "It causes the tree to shut down, so basically it looks like a tree that's not getting water. It's not, because the fungus has blocked up the water conducting tissues."

Trees in the red oak family, known for their pointed leaf tips, can die within a few weeks on contracting the disease. Those in the white oak family, with rounded leaf tips, can last up to several years. Regardless of the family, the trees are infected in one of two ways. One of them is insects carrying spores of the fungus to a freshly wounded tree.

Ball says, "They need an invitation to do spread those spores. So they need either a fresh pruning cut during April May or June, or storm damage." 

The other transmission happens below ground.

"The fungus can grow down into the root system of trees and then spread from one tree to another through root grafts. And root grafts are basically points where the roots of two trees have grown together," says Blaedow.

While infected trees can be hard to spot now that all trees are losing their leaves, the upcoming winter season is the best time to treat and remove diseased oaks to prevent the spread to neighboring oaks come spring.

For further reading on Oak Wilt, visit the DNR Oak Wilt Website.

According to the DNR, to prevent the spread of oak wilt, people should follow these management guidelines:

  • Trim oak trees during winter, if possible; it is best to remove diseased trees in the winter to avoid wounding neighboring trees.
  • Remove diseased trees before the following spring to prevent spore mat development.
  • Avoid wounding oak trees between April and July when sap beetles actively feed.
  • Treat wounds immediately with pruning paint if trees are wounded during the spring and summer.
  • Sever root connections to healthy trees prior to removing dead and diseased trees by trenching around diseased trees with a vibratory plow equipped with a five-foot blade.
  • Destroy infested wood or treat wood on site by debarking, chipping or drying the wood.
  • To dry wood properly, cover split wood with plastic and bury the edges for at least six months to kill the oak wilt fungus and any insects.

Both Blaedow and Ball suggest calling your city forester or an arborist if you suspect Oak Wilt on your property.









(Copyright 2012 by KARE. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed. )

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