MONTCALM TOWNSHIP — John Johansen lost seven ash trees last year to the emerald ash borer.
This year he estimates he will lose 17 more trees to another problem — oak wilt.
Oak wilt is a disease caused by a fungus that plugs the water-conducting system of oak trees. To block the spread of the fungus, trees produce gums and resins, which also plug the system, causing infected trees to die.
Johansen’s trees are the first reported case of oak wilt in Montcalm County, according to Jeremy Sova, district conservationist for the Natural Resources Conservation Service, a United States Department of Agriculture office in Stanton. Oak wilt also has been reported in Ionia County and Kent County.
“It’s devastating,” said Johansen of the disease. “In order to control it, you have to take some pretty drastic steps.”
Disease = death
Johansen, a member of the Montcalm County Board of Commissioners, noticed something odd in a portion of the forest on his Montcalm Township property in late September. Red oak leaves were rolling up and hanging or falling off the trees well before any of the other forest’s foliage.
The red oak leaves didn’t have the typical warm colors of autumn, but were a strange shade of bronze.
Johansen suspected oak wilt, which he had heard about before. He called Sova, who came out to the property. The two men couldn’t find any solid evidence of fungus pads under the bark indicating oak wilt.
Sova called a conservation district forester, who referred Sova to the Michigan Department of Natural Resources (DNR), which arranged for a Michigan State University Extension graduate student to visit the site and confirm the presence of oak wilt.
All oak trees can be affected by oak wilt, but red oaks are the most susceptible, according to the DNR Forest, Mineral & Fire Management Division and Michigan State University Extension.
Red oaks will die within a few weeks of becoming infected. White oaks are more resistant and the disease progresses more slowly.
Spread and prevention
Oak wilt can spread to adjacent healthy trees through root grafts, even to trees 50 feet away. The fungus also can be carried to new areas by sap-feeding beetles, which move spores from infected trees to healthy trees.
Beetles can also transfer the disease from infected firewood.
“It’s something that doesn’t spread very rapidly,” Sova said.
Wounding an oak tree between mid-April and mid-July can also lead to oak wilt. Wounding can occur from a lawnmower, pruning or be weather related.
While fresh sap is only attractive to sap-feeding insects for several hours after a wound occurs, beetles are numerous and widespread during this period and the risk of oak wilt being transferred is high.
“Typically by the time you see it it’s too late to do anything,” said Sova of the disease. “If it starts in one tree, it typically works in a circle. Oaks tend to grow in a group anyway.”
Oak wilt can’t be cured, but it can be controlled and prevented. Avoid injuring or pruning oak trees from mid-April to mid-July.
Stop the movement of the fungus by severing root grafts between healthy and infected trees. Removing infected trees without severing root grafts first is not effective because the fungus stays alive in the root system.
Removing an infected tree before the roots have been severed can actually speed up the movement of the fungus into surrounding trees.
Vibrating plows or trenchers with five-foot blades are the most effective way to break interconnected root systems.
Barriers must be placed far enough away from infected trees to ensure that the disease has been isolated in the root systems within the barrier circle. This includes trees that may not yet be infected, but are close enough to infected trees to be grafted.
Trees inside the barrier circle should be removed, cut and covered with a tarp for one year to prevent beetles from reaching the fungus pads.
Fungicides are also effective, but are expensive and must be applied by a licensed applicator using special equipment before or shortly after infection takes place.
‘Hopefully we can contain it’
Johansen plans on cutting down all the oak trees in the perimeter of his diseased trees and turning them into firewood, as well as pulling up the stumps and stacking them.
He’s concerned not only about his own property, but also about his neighbor’s virgin oak forest comprised of trees that haven’t been harvested since the late 1800s.
“We have the best variety of wood in this state,” said Johansen, who informed his fellow county commissioners about oak wilt at a recent board meeting. “The goal is to let people know that oak wilt has moved into Montcalm County. Hopefully we can contain it and it doesn’t move. It’s very serious to anyone who has timber.”
Sova encourages anyone with questions or concerns about oak wilt to call him at (989) 831-4212.
Facts about oak wilt
• Oak wilt is a disease caused by a fungus that plugs the water-conducting system of oak trees.
• Oak wilt can affect all oak trees, but red oaks are the most susceptible and will die within a few weeks of becoming infected.
• Signs of oak wilt include curled up leaves that turn an ugly shade of bronze and fungus pads underneath the tree’s bark.
• Oak wilt cannot be cured, but can be controlled and prevented. Don’t prune oak trees between mid-April and mid-July. Severe root grafts can occur between healthy and infected trees.
Source: The Michigan Department of Natural Resources Forest, Mineral
& Fire Management Division and Michigan State University Extension