CADILLAC — At the end of April, Michigan residents are ready to see the greening up of the countryside.
While the various trees and plants that are native to the state do that on their own, this time of year it also could include various projects including yard cleanups or the pruning or shaping of brushes, shrubs or trees. The Michigan Department of Natural Resources, however, is asking people to hold off pruning oak trees from mid-April through the summer because that time period is the key time for infection with oak wilt.
To keep oak trees healthy, don’t prune them from mid-April through the summer. That’s a key infection time for oak wilt, a serious disease that can weaken white oaks and kill red oak trees within weeks, according to the DNR.
“We’re asking residents to take extra precaution with their oak trees as spring gears up,‘ DNR Forest Resources Chief Deb Begalle said. “Waiting to prune until fall will go a long way in preventing the spread of this disease.‘
Oak wilt, caused by a fungus, has been reported throughout the Midwest, including Michigan. Trees in the red oak group, including black, northern red and northern pin oaks, have leaves with pointed tips and are most susceptible. Trees in the white oak group, including white and swamp white oak, have rounded leaf edges and are less susceptible.
Affected trees suddenly will begin to wilt from the top down, rapidly dropping leaves, which can be green, brown or a combination of both colors.
Oak wilt is spread above ground mainly by sap-feeding beetles that carry disease spores from infected trees, or wood cut from infected trees to fresh wounds on healthy trees. The infection also spreads below ground, through root grafts.
If you must prune or remove oaks during the April 15-July 15 risk period, or have a tree that gets damaged, the DNR suggests that all wounds are immediately covered with tree-wound paint or latex-based paint.
The DNR also suggests to not move firewood, especially if it comes from oak wilt-killed trees. If you suspect firewood is tainted by oak wilt, cover it with a plastic tarp all the way to the ground, leaving no openings. This keeps beetles from moving spores from the firewood to healthy trees. Once the firewood has dried at least a year and/or all the bark loosens, the disease can no longer be spread, according to the DNR.
Last year, the DNR created a team of foresters with the purpose of searching for and assessing threats to Michigan trees including hemlock woolly adelgid, oak wilt and Heterobasidion root disease. These threats pose a significant risk to oak, pine and other tree species integral to the health of Michigan’s forests and landscape, according to the DNR.
These efforts and more are chronicled in the DNR’s annual Forest Health Highlights report, which includes updates on issues including spruce decline, forest tent caterpillars and Japanese stilt grass. It details efforts to keep invasive pests such as the spotted lanternfly and the Asian longhorned beetle, both found in nearby states, from infesting Michigan trees.
“We are working with university, state, federal and community partners to tackle forest health issues in the most effective ways possible,‘ said Susan Tangora, forest health section manager for the DNR. “The U.S. Forest Service, the DNR and partner agencies also are sharing the cost of the work.‘
The forest health report also outlines what the DNR and others are doing to make sure rural and urban trees stay as healthy as possible — and the public can help.
The DNR has developed some interactive maps where people can report suspected problems or concerns on specific tree and pest issues. Check out the oak wilt map and the Heterobasidion root disease map on the Forest Health webpage to see where these problems are clustered and learn about efforts to fight them.
Find the current report at Michigan.gov/ForestHealth.