Oak wilt, a disease lethal to red oaks, is caused by a fungus that clogs the water-conducting vessels of infected trees, causing them to wilt and ultimately die. To prevent the spread of the disease, do not prune oak trees between April 15 and Oct. 15, and address any tree wounds or damage immediately during that period.

Oak wilt, a disease lethal to red oaks, is caused by a fungus that clogs the water-conducting vessels of infected trees, causing them to wilt and ultimately die. To prevent the spread of the disease, do not prune oak trees between April 15 and Oct. 15, and address any tree wounds or damage immediately during that period.

File photo provided by the Michigan Department of Natural Resources


Residents warned to watch out for oak wilt

By: K. Michelle Moran | Grosse Pointe Times | Published April 9, 2019

GROSSE POINTES — As if homeowners didn’t have enough to worry about with emerald ash borer and Dutch elm disease, now they need to also be vigilant about the deadly tree disease oak wilt.

Brian Colter, the forester for Grosse Pointe City and Park, said that as of press time, no cases of oak wilt have been reported in the Pointes, but it was discovered on Belle Isle about three years ago and is a potential threat. He said it’s most likely that the disease was brought to the island through firewood.

“It doesn’t seem like it’s been in the Grosse Pointes yet,” Colter said. “We want to keep it that way.”

Like Dutch elm disease, oak wilt is a fungal disorder. It’s often spread by small sap beetles that are drawn to the scent of a fresh cut on an oak tree. It can also spread via “the movement of fungal spores between shared roots of infected trees and surrounding oaks,” Ruth Marcy, a Michigan State University Extension master gardener, explained in an article she wrote about oak wilt control and management.

Oak wilt kills the trees by preventing water and nutrients from traveling throughout the tree, Colter said.

In Northern Michigan, Colter said, oak wilt “is an epidemic,” so one of the best pieces of advice he can offer is to urge residents not to bring firewood from homes and cabins up north to southeastern Michigan.

“Don’t move firewood, period,” said Colter, noting that this is how many tree diseases and pests have spread quickly throughout the state, not just oak wilt.

To stop the spread of this disease, oak trees shouldn’t be trimmed between April 15 and Oct. 15. Instead, they should only be trimmed when dormant, in the winter months.

“The problem with oak wilt is, it’s so deadly, there’s nothing you can do (after a tree is infected),” Colter said. “It can kill an oak in a couple of weeks.”

Red oaks are more vulnerable to oak wilt than white oaks. Ryan Wheeler, an invasive species biologist with the Michigan Department of Natural Resources, said the disease can weaken white oaks and kill red oak trees within weeks.

Red oaks have leaves with pointed tips and include black oak, pin oak, northern red oak and scarlet oak. White oaks have rounded leaf edges and include white oak and swamp white oak.

“Affected trees will suddenly begin to wilt from the top down, rapidly dropping leaves, which can be green, brown or a combination of both colors,” Wheeler said in a statement last year.

Although oaks aren’t as prevalent in the Pointes as they are up north — Colter estimates they only account for roughly 3% of the street trees in the Pointes — the ones that do exist tend to be stately and mature.

“(Oak wilt) still would be devastating, because the oak trees we have are large and majestic,” Colter said.

Marcy warned about how vital it is to address tree wounds immediately, whether those wounds are caused by cutting, lawn equipment or storm damage.

“Latex paint, clear shellac or pruning sealers are all good choices to create a protective barrier to disease-carrying beetles,” she wrote. “These tiny sap beetles are extremely attracted to fresh wounds, and have been known to arrive within 10 minutes after a wound is created.”

Oak wilt is difficult to diagnose, so Colter said homeowners need to bring out a certified arborist to analyze the tree. Certified arborists can be found on the Michigan Oak Wilt Coalition website.

Colter also said residents need to watch for pear trellis rust, a fungal condition that has been hitting pear trees in the Pointes for at least the last five years. Although he said he hasn’t seen this disease kill any trees yet, it’s not an aesthetically pleasing condition, as it produces orange splotches with a black dot on the leaves.

“I’m not personally treating any trees for this (condition), but there are local, reputable companies that are treating (them),” said Colter, adding that homeowners might want to have a prominent pear tree injected against pear trellis rust.

“Last year was a very bad year for it,” Colter said. “Every pear in the Grosse Pointes seemed to have it.”

For more information about oak wilt, visit www.MichiganOak Wilt.org.

Staff Writer Sarah Wojcik contributed to this report.