As spring approaches, East Lansing’s trees are leafing out in vibrant colors, bringing much-needed shade to neighborhoods and sidewalks. But oak wilt, spruce decline, and insect pests are challenging our arboreal environment.
Many long-time East Lansing residents remember when majestic elms lined Michigan Ave. and American chestnut and ash trees dominated the landscape of East Lansing. Now, because of diseases hitting those species, oaks, maples, hemlock, and blue spruce are our main suburban trees.
Mature trees are assets to East Lansing life (and property values), but the threat of the fungus Bretiella fagacearum, known colloquially as “oak wilt,” is looming large.
Oak wilt can attack and kill red oak trees in just a few short months. By late spring in Mid-Michigan, the fungus is all warmed up and producing spores by the billions. Insects feed on the fungus of an infected tree, then fly off to a wound site on another tree, spreading the disease.
First reported in Michigan in the 1970s, oak wilt is fatal to red oaks. The fungus grows rapidly and chokes the tree, giving it a wilted appearance. Leaves turn brown and drop much earlier than normal.
Local tree experts recommend early detection, treatment, and prevention of oak wilt, and consideration of alternative trees that can thrive in our community.
Prompt control of oak wilk is important. Oaks comprise about 10 percent of the forest in Michigan and oak wilt has the potential to kill hundreds of thousands of trees across the almost-20 million acres of forestland in our state alone.
“Pruning, storm damage, nail holes, mower gashes, and other wound-opening events create a place for fungus spores to infect a new tree,” explains local arborist Alex Ellis of Ellis Arbor Care.
“Pruning is strongly discouraged during warm months for oaks, when temperatures are consistently above 60 degrees,” Ellis says.
In our area, this no-prune period generally falls from mid-April through mid-September. Pruning oak trees only in cooler months, between fall and spring, means opening tree wounds when the fungus and the fungus-spreading insects are relatively inactive.
“There are problems that may cause similar symptoms in our neighborhood trees,” Ellis notes, “so it is important to have questionable trees tested.”
Michigan State University’s Plant & Pest Diagnostics service accepts samples year-round.
Fungus is also a contributing factor to spruce decline. Colorado blue spruce is a popular garden tree here in East Lansing, but is better adapted to drier climates. Our heavy rainfall and poorly drained soils can provide a good habitat for fungus to overtake the trees.
Many local blue spruce trees are afflicted, showing significant needle drop beginning on the lower limbs. Norway spruce seems to fare much better in our area. MSU provides additional information on spruce decline and conifer alternatives to blue spruce.
Suburban trees face many other challenges too.
Crown rot disease can set in for trees that have soil or mulch piled up too high around the trunk.
“This area [of the tree] is important for gas exchange,” Ellis explains, “and should be exposed.”
Ellis recommends leaving this area exposed when planting new trees and excavating the trunk to expose the very top of the root “flare” on mature trees.
“Often in the nursery pot, the tree is already buried too deep, and when people use that soil line – when they match that line to plant in the garden – it’s already too high.”
Ellis recommends gently excavating the root crown.
“Don’t scrape or damage bark. If you can’t see a root flare, just gently push dirt away to expose the tops of the first significant roots.”
While some mulch helps protect trees from drought and weeds, too much mulch can create an environment that promotes rot.
“Maples and dogwoods can be very sensitive to being buried too deep and can become predisposed to stress and disease,” Ellis told ELi, recommending owners of these trees “dig down through the dirt and mulch, to the first larger roots.”
Insect pests such as the emerald ash borer, wooly adelgid, and Asian longhorn beetle are making meals of many Mid-Michigan trees, dramatically changing our wilder landscapes as well as local neighborhoods. Treatment relies on early detection or planting trees that don’t host these problems.
“If you are in the market for a new tree to plant, don’t be discouraged,” says Burt Cregg, who conducts research and runs extension programs at Michigan State University. “Most of these pests and diseases are specific to certain trees. Emerald ash borer only kills ashes, oak wilt only kills red oaks, spruce decline only affects blue spruce, and wooly adelgid only affects hemlocks. Asian longhorned beetle is a generalist – it can attack many types of trees – but so far has not been found in Michigan – knock on wood.”
“There are still plenty of trees that people can plant,” according to Cregg, who names his favorite garden trees well-suited for our area as including the American hornbeam, bald cypress, hackberry, hybrid elms, Kentucky coffeetree, London planetrees, swamp white oak, and tulip poplar.
MSU Extension also offers a list of trees that help to not spread diseases here in Mid-Michigan.
“In addition to conifers in the bulletin, we could include white spruce, black hills spruce, arborvitae, white pine, and Norway spruce,” Cregg says.
If you suspect a problem with one or more of your trees, you can contact MSU Extension or a local arborist.