Common Tree and Shrub Diseases in Michigan

Apple Scab

Apple Scab Apple damage
Apple Scab leaf damage
Apple scab, caused by the fungus Venturia inaequalis, is an unsightly infection which affects leaves, fruit and twigs. Infections are most common on apple and crabapple trees but both pear and hawthorns are also frequently infected. Spring spores develop into brownish-green spots on the leaves or fruit. As the infection progresses, the spots on the fruit become darker and more prominent. Leaves will turn yellow and drop off prematurely in summer. Fruit will become deformed and/or drop off prior to ripening. Repeated annual infections can weaken the tree making it more susceptible to other insect or disease problems.


Fungicide applications are needed for disease activity during wet seasons. Multiple foliar sprays and/or trunk injections are preventive and need to be timed properly for effective control.


Anthracnose leaf edges
Anthracnose damage
Anthracnose (leaf blight) is a fungus disease impacting a variety of tree species, including: Ash, Birch, Dogwood, Elm, Hickory, Linden, Maple, Oak, Sycamore and Walnut. Spores are transported to new buds and shoots in spring. This disease is enhanced by cool, wet conditions. Signs of anthracnose are tan to red-brown lesions that extend along the veins and edges of the leaf. Considerable defoliation, sometimes complete leaf loss, is expected.


Identifying and foliar spray treatments will target this disease to minimize fungal activity. Prune out infected twigs to reduce the spread of anthracnose. Keeping trees in good vigor with deep watering during droughts, nutrition with fertilization and control of insects can help decrease susceptibility to the disease.

Diplodia Tip Blight

Diplodia tip blight damage
Diplodia tip blight (Sphaeropsis sapinea) is a serious disease of exotic pines such as Austrian pine and Scots pine. Tip blight has been documented on 20 pine species throughout the Central and Eastern United States. Infection spreads from needles to twigs and can kill trees by clogging the vascular flow of water and nutrients. Stress from drought, compaction, mechanical damage and other abiotic factors make this disease worse.


Keeping trees in good vigor with deep watering during droughts, nutrition with fertilization and control of insects can help decrease susceptibility to the disease. Fungicide control is most effective in early spring.

Dothistroma Needle Blight

Dothistroma Needle Blight damage
Dothistroma Needle Blight close up
Dothistroma needle blight is a common needle disease that can affect several species of pine trees. Dothistroma needle blight first appears as dark green, water-soaked spots on the needles. The spots become tan, yellow, or reddish-brown, and may encircle the needles to form bands. The tip of the needle beyond the band eventually dies leaving just the base of the needle.


Early identification of Dothistroma Needle Blight can prevent major damage to individual trees and prevent the spread to nearby trees. Protecting new growth as it emerges is very important.

Oak Wilt

Oak Wilt damage
Oak Wilt on leaves
Oak wilt is a vascular disease of oak (Quercus sp.) caused by the fungus Bretziella fagacearum. The fungus is spread below ground via root graft transfer and above ground by nitidulid picnic beetles and possibly oak bark beetles. Members of the red oak family can die rapidly (4-6 weeks) while members of the white oak family have more tolerance and may live longer. The disease is widespread throughout the eastern and central United States.


1) Treat high value asymptomatic oaks that are within root-grafting distance of infected white oaks. Preventative systemic treatment and early detection are vital to saving our oak trees.
2) Never prune oak trees from April through June. Delay pruning until dormant season to further minimize contamination risk.

Powdery Mildew

Powdery Mildew on leaf
Powdery Mildew example
Powdery Mildew, Blumeria graminis, is a common and relatively recognizable disease affecting a wide range of host trees. This disease infects plants during times of high humidity, most often in the late spring through summer. Symptoms are most commonly found on the upper side of leaves, but can also infect stems, buds, flowers, and fruit. Proactive fungicide treatment is necessary to control this unsightly fungus. This disease occurs across the entire United States.


Preventative fungicide applications are helpful in controlling symptoms. Proper timing, before symptoms appear, is crucial to getting good control. Good cultural control includes: spacing plants appropriately, pruning for air flow, removing dead plant material and not watering from overhead.


Chlorosis damage
Iron or manganese chlorosis describes an intervenial condition in which a tree’s foliage loses its healthy green color and fades to a pale green or yellow. Over time, this condition will cause premature leaf drop, slow growth and eventually tree death. Chlorosis inhibits photosynthetic food production causing a tree to starve. Trees growing in compacted, nutrient deficient and poorly drained soils are more susceptible to chlorosis.


Soil fertilization treatments produce the best results. Iron and manganese replacement address the root of this disease.

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