Skip to content 
With more than 100 native tree species, Southeast Michigan is a tree-lover’s dream. From delicate understory species like redbuds and ironwoods to white pines, sycamores, and other towering giants, beautiful trees abound in the Great Lakes State.
But while our climate, soil, and habitats are capable of supporting an array of species, there are a number of important tree diseases common to the region. Some of these may even threaten the trees growing on your property. We’ll share some of the most significant tree diseases found in southeast Michigan, so that you can keep an eye out for them and avoid the need for emergency removal or other costly services.
9 Common Tree Diseases in Southeast Michigan
There are likely hundreds of different tree diseases that can affect Michigan trees. However, most are relatively rare and unlikely to show up in the trees in your yard or commercial property. But the following diseases are fairly common and represent a legitimate threat to your trees.
1. Oak Wilt
Caused by a fungus called Bretziella fagacearum, oak wilt is a particularly heartbreaking tree disease, as it targets some of the most beautiful and valuable trees in the state — our native oaks.
Oaks in the red oak group are at the highest risk, while those in the white oak group are not as vulnerable to the pathogen. This means that northern red oaks (Quercus rubra), pin oaks (Q. palustris), and black oaks (Q. velutina) are at high risk, while white oaks (Q. alba), bur oaks (Q. macrocarpa), and swamp white oaks (Q. bicolor) are not as likely to succumb to this disease.
Oak wilt tends to cause sudden leaf wilt and browning. The symptoms often begin at the top of the tree’s canopy before moving down through the tree. The disease is spread in two primary ways: root grafts between infected and non-infected trees and via the feeding habits of beetles. This is part of the reason oaks should never be pruned during the active growing season – the freshly cut limbs attract the beetles.
Oak wilt is usually fatal, though treatment with propiconazole proves effective in some cases (particularly with white oaks that have been infected). Propiconazole can also be used as a preventative treatment, and it tends to be more effective when used this way.
2. Anthracnose
Anthracnose is a catch-all term that refers to a group of fungal diseases that primarily cause foliar symptoms. Infected trees often exhibit leaf spots, leaf blotches, wilting, and dieback, and premature leaf drop often follows. Entire twigs may dieback in some cases. Anthracnose outbreaks tend to be most common following cool, wet spring seasons, when tree leaves remain damp for long periods of time.
Different anthracnose-causing fungi attack different tree species. For example, Apiognomonia veneta attacks sycamores (Platanus occidentalis), Gnomoniella fraxini attacks ash trees (Fraxinus spp.), and Apiognomonia quercina infects oaks (Quercus spp.).
Unfortunately, anthracnose is generally not treatable once symptoms develop, though some fungicides can help prevent anthracnose symptoms from developing if applied before bud break. Other prevention strategies — such as pruning to promote airflow, disposing of dead plant material properly, and watering trees correctly — can also help protect trees.
Fortunately, anthracnose is usually a cosmetic issue, which won’t kill trees (though repeated attacks in successive years may weaken them over time). However, a few forms, such as dogwood anthracnose (Discula destructiva), can be lethal.
3. Apple Scab
Apple scab is another fungal disease, caused by an organism called Venturia inaequalis. Apple scab is quite common, and some trees suffer from repeated infections that occur in the late spring and summer. Crabapple trees (Malus spp.) are the most common victims, but it can also infect some pear trees (Pyrus spp.) and mountain ashes (Sorbus aucuparia).
On the plus side, apple scab is typically a cosmetic issue that doesn’t threaten the overall health of a tree. It usually causes symptoms like leaf distortion, curling, or the appearance of dark, velvety spots. The fruit may also become compromised, leading to deformities and premature dropping.
Nevertheless, the damage to crabapple leaves and fruit can be quite severe, and many infected trees will drop all of their leaves by mid-summer. Additionally, repeated infections can weaken a tree, making it vulnerable to secondary infections or pest attacks.
Fungicides can be used preventatively if applied before bud break, but they’re not effective once symptoms have developed. Proper pruning and irrigation practices can also help prevent the infection from occurring, and there are resistant cultivars available, which are largely immune to apple scab.
4. Cedar-Apple Rust
Cedar-apple rust is a very interesting tree disease, as it affects two different types of trees: eastern red cedar (Juniperus virginiana) and apples or crabapples (Malus spp.). In fact, the disease — called Gymnosporangium juniperi-virginianae by arborists — needs both host species to complete its life cycle.
The disease spends most of its life living on cedar trees. After infecting the tree, it will produce long, orange-colored, horn-like structures, called telial galls or telial horns. These horns release spores in the spring, which find their way to crabapple trees. Later in the summer, the crabapple trees will begin developing orange leaf spots, which eventually release spores. These spores find their way back to cedar trees, restarting the cycle.
Cedar-apple rust doesn’t usually kill either species, and it rarely causes serious harm to cedars at all. Crabapple trees, however, may lose most of their leaves or ruin the quality of the fruit. Successive infestations over the course of many years may eventually weaken the tree enough to make it susceptible to other pathogens.
Cedar trees don’t need to be treated for cedar-apple rust, but fungicides can be used to help protect crabapple trees. Additionally, you can help reduce the chances of your apple trees being infected by removing the telial horns gropwing on cedars early, before they can release spores. You can also install resistant crabapple varieties or simply plant the trees far enough apart (at least 300 feet) to break the lifecycle.
5. Needle Cast Diseases
Needle cast diseases attack conifers and cause the older, inner needles of the trees to fall off prematurely. The disease most commonly starts near the bottom of the tree and works its way upward, causing the needles to turn yellow, purple, or brown before they drop. Over time, the disease causes trees to look sparsely foliated and thin.
A variety of conifers are susceptible to needle cast diseases, including our native pines (Pinus spp.). However, infections in properly cared for pines is relatively rare. Instead, it is nonnative tree species — including Norway spruce (Picea abies) and Colorado blue spruce (P. pungens) — which are most commonly infected. Colorado blue spruce, in particular, is a frequent victim of this disease, as the tree is not well-adapted to Michigan’s humid climate.
This disease can kill trees in some cases, but it is usually just an aesthetic issue. Nevertheless, trees infected by the pathogen — Rhizosphaera kalkhoffii, in the case of the Colorado blue spruce — will have trouble producing enough food thanks to their reduced crown density, which will weaken them.
Fungicide applications can help prevent infection in Colorado blue spruces, but these treatments will be necessary several times per year. Instead, it is simply preferable to plant trees that are better suited for Michigan’s climate.
6. Cytospora Canker
Needle cast diseases aren’t the only problem for Colorado blue spruces in Michigan; Cytospora canker (Cytospora spp.) is also a significant threat. The fungus can also attack other spruces (Picea spp.), Douglas-firs (Pseudotsuga menziesii), poplars (Populus spp.), and willows (Salix spp.), but these trees are rarely as affected as the blue spruce is.
Cytospora generally attacks trees that are already weakened by other stressors, such as insect attacks or drought. Poor site selection is also something that can predispose trees to infection, which is often why Colorado blue spruces contract the disease.
Cytospora can cause a variety of symptoms, but resinous cankers are one of the most common signs of infection. They tend to cause sunken and discolored areas of bark, and the bark will generally slough off over time. Sometimes, you may note tiny black dots on the canker during moist weather. These are the fungal fruiting bodies, which help spread the disease.
There is no cure for Cytospora canker, so prevention is the best strategy. This means planting trees in conditions favorable to the species’ needs, pruning the trees properly, providing fertilizer as necessary, and maintaining a 2- to 4-inch-deep layer of organic mulch beneath the dripline. It’s also important to provide supplemental water to trees during periods of drought.
7. Fire Blight
Another disease that affects apple and crabapple trees, fire blight is named for its tendency to make infected branches look scorched or burned. It can also cause oozing cankers in some cases, and infected blossoms will generally turn black and fall off shortly after opening. Infected fruit may shrivel before turning brown or black and falling to the ground.
Unlike most of the other diseases we’ve discussed, fire blight is caused by a bacterium — Erwinia amylovora — rather than a fungus. It’s especially problematic for orchards, as it spreads quickly from one tree to another, which can lead to entire groves becoming infected. Worst of all, it can kill large branches or entire trees.
Unfortunately, fire blight can be spread in several different ways. Insects and pruning tools can transfer the bacterium from one tree to another, as can splashing rainwater. The disease may also be carried in the wind, causing it to spread far and wide across the land.
You can’t cure fire blight once it occurs. Accordingly, prevention and management are the best strategies. Resistant cultivars exist, and you can occasionally prune infected branches quickly enough to halt the spread within a given tree. Just be sure to sterilize your pruning tools after making the cuts.
8. Verticillium Wilt
Returning to fungal pathogens, verticillium wilt (Verticillium spp.) is another threat to many Michigan tree species, including maples (Acer spp.), redbuds (Cercis canadensis), elms (Ulmus spp.), ashes, and Tuliptrees (Liriodendron tulipifera), among others. But unlike some other fungal diseases, verticillium wilt is soilborne. In fact, this fungus can survive in soil samples for up to 10 years, so it is almost always a potential threat.
Verticillium wilt fungus enters a tree via its root system – especially when the roots suffer damage, such as from repeated encounters with lawn mowers or string trimmers (which further highlights the importance of placing mulch under a tree’s drip line). Once inside the tree, they begin blocking its xylem (wood tissue), which prevents water from moving up the trunk. Sudden wilting usually occurs soon thereafter, leading to the loss of entire branches.
Verticillium wilt may kill trees that aren’t properly supported, and because the fungus will remain in the soil, trees planted to replace those lost from the initial infection will often succumb as well. The only way to avoid repeated bouts with the disease is by replacing trees with resistant species, varieties, and cultivars.
There is no cure for verticillium wilt once it infects a tree, so management strategies are the best option. This entails doing things like pruning weakened branches, providing supplemental water and fertilizer when needed, and maintaining a thick mulch layer.
9. Armillaria Root Rot
One of the most troubling diseases in this entire list, armillaria root rot, is caused by fungi in the genus Armillaria. Armillaria is particularly worrying because it causes white rot in the roots or at the base of a tree’s trunk. This makes the tree very brittle, which can cause it to fall over suddenly and with no warning.
Unfortunately, Armillaria can affect a wide variety of hardwoods and conifers, so few trees are immune to infection. However, it rarely infects healthy trees; it most commonly attacks trees that are already stressed by drought, insect infestation, disease, or some other factor. This means that you can usually protect your trees by simply providing them with good supportive care.
Armillaria may cause canopy thinning, branch dieback, or premature fall color. However, one of the most important symptoms is the appearance of honey-colored mushrooms with white gills growing on or near the base of the tree.
Armillaria cannot be treated once it has infected a tree. And because of the risk of total tree failure, infected trees must often be removed promptly. This means that prevention — primarily by providing good growing conditions for the tree — is the best course of action.
General Signs To Watch For: Michigan Tree Disease Symptoms
Because tree diseases often present a variety of symptoms, and many of them are surprisingly subtle, it can be tricky for homeowners and property managers to know when a tree is healthy and when it has been infected by some type of pathogen.
So, while it is always wise to simply contact a professional arborist when in doubt, there are a few common signs and symptoms you’ll want to watch for. These don’t necessarily indicate that your tree is sick, but they should prompt you to have it assessed.
Some of the most important signs and symptoms that you should look for include:
- Mushrooms or conks growing on or around the tree
- Fluid leaking out of the trunk or major branches
- Large dead limbs
- Leaves that are yellowish, curled, or shriveled
- Leaves that have spots or areas that look burned
- Leaves with raised bumps or projections
- Leaves that are coated in dark-colored material
- Trees with large hollows
- Large branches falling from the tree
- Premature leaf drop
These kinds of signs don’t always indicate the presence of a disease; some may indicate the presence of pests instead. For example, raised bumps on leaves may be caused by diseases, but they can also be caused by insects.
On the flip side, some of these signs may not indicate anything is wrong with your tree at all. Mushrooms provide a great example of this — some mushrooms are associated with tree decay, while others are produced by important symbiotic fungi, called mycorrhizae. These fungi actually help support tree health.
This all simply illustrates the need to have a professional arborist inspect your trees if you notice any of these signs.
Get the Treatment Your Southeast Michigan Trees Need!
Whether you suspect that your trees are suffering from one of the diseases above, or you’re experiencing problems with pests, drought stress, or poor structure, the professional arborists at Treemendous Tree Care can help!
Whether you’re in Roseville, Warren, Waldenburg, or anywhere else in the greater Detroit area, our arborists can provide the tree-care services you need, from routine pruning and hazard tree removal to stump grinding and crane-assisted removals, designed to keep your trees healthy and thriving.
But to give your trees the best chance at a full recovery, you can’t delay. Book your free estimate today and see the Treemendous Tree Care difference!
