Maple Tree Diseases and How to Treat Them

Diseased maple tree leaf

Symbolic of strength, endurance, balance, and longevity, maple trees have not only rooted themselves in our world culture but also in our landscape designs. Perfect as an accent piece or to line a long driveway, there’s no denying the beauty and majesty these towering plants exude. That is, unless a stealthy attacker attempts to sap these trees of their splendor — and even their lives.

Typically, maple trees can live healthy lives for up to 300 years, but sometimes they fall prey to illness. These can include diseases, such as tar spot, verticillium wilt, anthracnose, leaf scorch, powdery mildew, and lichen, to name a few. Treatment ranges from pruning dead branches to removing the entire tree and fumigating the soil to doing nothing at all, depending on the infection.

So, what’s ailing your maple? Let’s take a look at the possibilities below to find out.

Maple Tree Diseases

The majority of maple tree diseases are purely cosmetic and don’t threaten the life of the tree. These types of health conditions generally affect the leaves, producing unsightly leaf spots and barren tree limbs. Infections capable of killing these plants tend to attack a tree’s internal systems, invading via the roots. Here’s a breakdown of some of the most common maple tree diseases from most to least serious.

1. Verticillium wilt

A fungal infection of the soil that penetrates a tree’s roots, verticillium wilt takes down a maple tree’s vascular (or circulatory) system. When this happens, water and nutrients are unable to reach branches and leaves. Dead leaves will fall to the ground and the soil will reabsorb the fungus, potentially setting off a wider infestation.

Symptoms: Wilted, yellowing leaves on one side of the tree; stunted leaf growth and leaf loss; discolored wood under bark
Causes: Soil-based fungusverticillium dahlia” or “verticillium albo-atrum”
Treatment: No cure, but some trees can recover with proper care. In severe cases, remove tree, fumigate soil, and plant a wilt-resistant species in its place. The best treatment is prevention through proper maintenance.
Season: Summer, typically July and August
Risk Level: Low in terms of its prevalence – most maple trees will not contract it. Mild to severe in that some infected trees can live a long time, declining slowly, while others must be fully removed and destroyed.

2. Sapstreak

Sapstreak disease
Manfred Mielke / CC BY 3.0

Sapstreak gets its name from the dark staining that forms in a star-shaped pattern on the rings of a tree’s chopped trunk. It threatens sugar maples, specifically, and enters through damaged roots. Once inside, this fungus moves unseen, preventing water and nutrients from reaching branches and leaves.

Symptoms: Smaller than normal leaves at the crown, discolored wood, and bald spots
Causes: The fungus “ceratocystis virescens”
Treatment: None other than prevention by protecting roots from damage. Some trees recover; others must be completely removed.
Season: Late spring, early summer
Risk Level: High. Remove infected trees to keep disease contained.

3. Root rot

Root rot

Most common in wet, poorly drained soil areas, root rot attacks the healthy tissues of the plant. This leads to a compromised vascular system, meaning the maple is not able to receive the water and nutrients it needs to survive.

Symptoms: “Fruiting structures” forming on bark along trunk and roots; in case of Phytophthora, “bleeding” cankers appear on wood.
Causes: Most common cause is the Phytophthora fungus; other fungal causes are Fomes, Ganoderma, and Laetiporus
Treatment: Total tree removal
Season: Spring rainy season
Risk Level: Serious. This is a fatal disease.

4. Tar spot

Black tar spot on sugar maple
Saforrest / CC BY-SA 3.0

While not life-threatening, tar spot is a fungal infection that affects maple tree leaves. Leaves can have one to several spots of varying sizes at a time, which may lead to premature leaf drop.

Symptoms: Begins as yellow spots on leaves before turning into black, tar-like spots
Causes:  The Rhytisma fungus
Treatment: None. Prevention is the best method and can be done by clearing away infected leaves that have fallen to the ground.
Season: Late summer, early fall
Risk Level: Low. Not life-threatening to the tree; only affects its appearance.

5. Anthracnose

Anthracnose disease on leaf
Debra Roby via Flickr/CC By 2.0

Affecting both maple leaves and tree branches, anthracnose becomes active in wet weather conditions. Branches and leaves located lower to the ground and toward the inside of the tree are more susceptible to infection.

Symptoms: Varied, depends on maple species. Includes shriveled leaves, discolored streaks on leaf veins, and curled leaves with brown spots.
Causes: Several fungi, including Discula and Kabatiella
Treatment: No treatment other than pruning dead branches and twigs and raking away fallen leaves.
Season: Spring
Risk Level: Low, cosmetic only.

6. Powdery mildew

Powdery Mildew
Jerzy Opioła / CC BY-SA 4.0

Different types of powdery mildew affect different types of maple trees. But in every case, this disease is not harmful, as the powdery substance merely sits atop leaves. The roots system is never invaded, and the fungus does not eat away at the leaves.

Symptoms: Appearance of white, powdery substance on leaves
Causes: The Phyllactinia fungus
Treatment: None needed; the fungus can be brushed off or removed with horticultural oil, though.
Season: Late summer and autumn
Risk Level: Low

7. Lichen

Lichen
Brewbooks via Flickr/CC By SA 2.0

When fungi and algae or cyanobacteria couple up to form a symbiotic relationship, a new existence called a lichen is formed. Preferring moist environments, lichens thrive on tree bark and use energy from the sun to make food. Since these growths do not feed on the tree itself, they cause no harm to it.

Symptoms: A crust-like, leaf-like, or tube-like growth on tree bark; may have a bluish tint to it
Causes: An organism composed of fungi and algae or cyanobacteria
Treatment: Prune affected branches; manually pull of the lichen
Season: Lichen can occur at any time of year
Risk Level: Low; does not harm the tree

8. Leaf scorch

Rather than a fungal, viral, or bacterial infection, leaf scorch can occur in the summer when the weather is hot and dry. The plant hasn’t been able to transport enough hydration to its leaves, so in turn, their edges begin to curl and turn brown.

Symptoms: Dried up leaves that turn brown
Causes: Hot, dry weather; low soil moisture
Treatment: Supplemental irrigation and mulching to maintain soil moisture; prune dead limbs
Season: Summer, particularly July and August
Risk Level: Low; not life-threatening

When to Call a Professional

For cosmetic imperfections like leaf discoloration and bark growths, professional treatment is not necessary. But if your maple contracts deadly diseases, such as verticillium wilt, root rot, or sapstreak, a call to the experts is essential. At LawnStarter, we’ve got plenty. Enter your ZIP code, create your account, and choose an expert from the list of locals in your area. A certified arborist will come out to your property to give your trees a little TLC.

Main image credit: Juandev / CC By-SA 3.0

Andréa Butler

Andréa Butler

Descendant of the Fulani tribe, Gettysburg-obsessed Marine Corps brat, and lover of all things writing and editing, Andréa Butler launched Sesi magazine and has penned articles for sites, such as LivingSocial, Talbot Digital, Xickle, Culturs magazine, and Rachel Ray. Andréa holds a B.A. in English from the University of North Carolina at Greensboro and an M.A. in magazine journalism from Kent State University.