ANTIGO — Local forestry officials are taking steps to curb the spread of a fungal disease known as oak wilt that has been killing an increasing number of oak trees in the eastern half of the county in recent years.
According to Linda Williams, a forest health specialist with the Wisconsin DNR, the disease is deadly to trees in the red oak group — including the northern red oak, northern pin oak, and black oak — which are most-easily recognized by their pointed leaves. In northern Wisconsin, the high-risk period for overland transmission of oak wilt spans from April 15 to July 15.
“During this time, if oaks are pruned or wounded or branches break, they can attract the beetles that carry the fungus from one tree to another,” Williams wrote in an email. “The beetles are attracted to those fresh wounds and they can scrape some fungal spores off their bodies as they feed, and if the tree is one of the red oak group, that tree will be dead from oak wilt by the end of the growing season…Once a single tree has died from oak wilt, the fungus then moves down into the root system and can move to nearby trees through root grafts between trees. Over the years, the fungus will continue to move outwards and kill additional oaks as it slowly moves through the connected root systems.”
Langlade County Forest Administrator Al Murray described oak wilt as a “growing problem” in the county, though one that so far has been found mostly in the east and central east portions of the county, as well as in a few pockets north of Post Lake.
“Years ago, we started off with about six small patches,” Murray said. “Last year, we increased up to about 13 separate patches, and this year we’re looking at some patches that have interspersed trees across hundreds of acres.”
Murray mentioned oak wilt in the same breath with several other diseases trees can develop due to beetle activity.
“It’s pretty similar to the old Dutch elm disease,” he said. “The beetles feed on that fungus and they feed in those trees, and the spores from the oak wilt fungus are just spread by the beetles flying to different locations. Beetles aren’t real great flyers, but if you get tall oaks that are on top of a big ridge, they can float for a long way.”
One reason for optimism, he said however, is the fact that beetles only carry the fungus to mature trees.
“It’s a little bit different than emerald ash borer. Emerald ash borer will actually kill all of the trees regardless of size,” Murray said. “So there is some hope, but we need to get ahead of it to make sure we have regeneration of oak going before the trees are dead. If we can get acorns on the ground and get seedlings established, we can actually take out all the trees and let the young trees go.”
The department will soon try to “get ahead of it” by applying a herbicide treatment to infected oak trees — and also to oaks in the immediate vicinity — to attempt to contain the spread. It has not always worked.
“We actually do within 100 feet around those trees so we get all of the oak trees,” Murray said. “So that’s what we have been doing, but some of the areas that we have treated that way are some of the areas that we still had it spread.”
The uptick in the fungal disease’s spread has led the forestry department to improvise its plans regarding lumber sales.
“We’re just about ready to set our bid dates for our fall sales, and we actually pulled some of the other non-oak sales off and we’re actually going to do some oak salvage to add to our sale volume. We kind of stopped mid-stream and our main priority now is to try to slow down the spread of that oak wilt,” Murray said.
He went on to explain that failing to deal with the oak trees that the disease has already killed could lead to a problem that could harm the environment and even endanger humans.
“If oak wilt comes through and we don’t try to stay ahead of it, we end up with all kinds of dead oak trees that end up falling on the ground, and what happens is the fire danger goes up,” Murray said. “The risk of an area burning hot and long is more if we don’t stay ahead of keeping that amount of dead material from being on the ground.”
Williams advised landowners to also use herbicide to kill oaks directly grafted to other diseased trees at the roots in order to get ahead of the disease as it attempts to spread underground from one root system to another.
“Education is a big part of slowing the spread of oak wilt,” Williams said. “It’s important for people who are doing yard work in the spring to wait to prune oaks until after July 15, or if pruning must be done during the high risk time (April 15 — July 15) they should immediately paint the pruning wound so that the beetles can’t access the fresh wood.”
Murray made note for the public that some areas suffering from oak wilt contagion will be clearcut in the near future.
“The impression that we’re just out cutting these big oak trees for no reason [will be wrong]. We’re going to be cutting them to make sure we can capture the value, and it’s also to try to let the seedlings get the sun so we can ensure oak is still back there in the future,” he said. “I think some of the property owners in that east area, especially around the Sherry Rd. area, contacting us to make sure that they’re trying to address oak wilt on their properties too would be important. We can go out and do it on county property, but if the neighboring property owners are still allowing oak wilt to remain on their lands, it’s just going to spread from their properties also. So we’re being proactive and we’re trying to get ahead of it so we don’t end up with a whole county that’s infested with oak wilt that we can’t catch up with.”
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