By the JCS Tree Care team · Led by an ISA Certified Arborist · Updated June 2026
The short version: The tree problems you’re most likely to run into here are oak wilt, Dutch elm disease, spongy moth defoliation, and the general decay that comes with aging trees. Most are manageable if caught early, and not every infected tree has to come down — but each is a reason to have the tree assessed. The one prevention step every oak owner should know: don’t prune oaks in spring or early summer. Concerned about a tree? Get a free on-site assessment, or call (248) 965-9035.
Oak wilt
Oak wilt is a fungal disease that’s especially aggressive in red oaks, which can die within a single season once infected. It spreads two ways: underground, through roots that have naturally grafted between neighboring oaks, and overhead, through small beetles that are drawn to the scent of fresh cuts and carry fungal spores from tree to tree.
The most important thing a homeowner can do is timing: avoid pruning or wounding oaks during the high-risk season — roughly mid-April through mid-July — when those beetles are most active. The safest time to prune oaks is winter. If an oak is wounded or storm-damaged during the growing season, the wound should be sealed right away. Where oak wilt is confirmed, managing it can involve removing the infected tree and, in some cases, severing root connections to nearby oaks to stop the underground spread.
Dutch elm disease
Dutch elm disease is a fungus spread by elm bark beetles that has killed most mature American elms across the region over the decades. Surviving older elms and newer disease-resistant plantings still need watching — early symptoms include leaves wilting and yellowing on individual branches (“flagging”) in summer. Caught early in a valued elm, there are management options; advanced infection usually means removal.
Spongy moth (formerly gypsy moth)
Spongy moth caterpillars defoliate oaks and other hardwoods, and in outbreak years they can strip a tree’s leaves. A single season of defoliation usually won’t kill an otherwise healthy tree — it pushes out new leaves — but repeated years, or defoliation on a tree already stressed by drought, disease, or root damage, can drive it into decline. The concern is rarely one bad year; it’s the cumulative stress.
Decay and root problems
The quietest problem is the most common: aging trees accumulate internal decay and root issues that aren’t visible until something fails. Mushrooms or shelf-like conks at the base, soft or crumbling wood, and dead sections in the crown are the outward signs. Root damage from construction, trenching, or paving can also kill a tree slowly over several seasons.
Emerald ash borer — historical context
You’ll see emerald ash borer (EAB) mentioned often in Michigan tree care, but it’s largely history here: EAB swept through southeast Michigan years ago and effectively wiped out the area’s ash trees, which is why a healthy mature ash is a rare sight in Oakland County now. It’s worth knowing as the clearest local example of how fast a single pest can reshape a landscape — and as a reminder to act early on any declining tree rather than waiting.
When a disease or pest means removal
Removal becomes the answer when a tree is dead or more than about half dead, when decay has compromised the trunk’s structure, when oak wilt or advanced Dutch elm disease has taken hold, or when a declining tree sits where a failure would hit a target. Many other cases can be pruned, treated, or monitored. The way to know which applies to your tree is an on-site assessment by an ISA Certified Arborist.
Frequently asked questions
When should I not prune my oak trees?
Avoid pruning oaks during the high-risk season, roughly mid-April through mid-July, when beetles that spread oak wilt are most active. Winter is the safest time.
How do I know if my oak has oak wilt?
Rapid leaf browning and drop in summer, often from the top down, is a warning sign — especially in red oaks. Because it spreads fast and to nearby oaks, get a suspected case assessed quickly.
Are ash trees still a problem in Oakland County?
The area’s ash were largely lost to emerald ash borer years ago, so mature ash are rare here now. It’s mostly a historical example at this point.
Does spongy moth kill trees?
Usually not from one season — healthy trees re-leaf. Repeated defoliation, or defoliation on an already-stressed tree, can cause decline.
Can a diseased tree be saved?
Often, if caught early, through pruning or treatment. Advanced disease or structural decay usually means removal. An assessment determines which.
