13 Common Maple Tree Problems and Diseases – Dengarden

Charlotte formerly worked as an editor of a garden channel and has extensive knowledge of plant care.

What's wrong with my maple tree?

When I worked as an editor of a gardening channel, people often asked me how to identify and address common maple tree pests, diseases, and problems. While maple trees can suffer from a number of general problems, verticillium wilt seems to be the most common and dangerous disease plaguing maple tree owners.

The fungi that cause verticillium wilt affect the tree's vascular system and cause symptoms of wilting and yellowing leaves that are concentrated in one particular area. Failure to control verticillium wilt can kill your tree, so it is important to correctly identify the disease and quickly remedy the problem.

Whether you don't have any idea what anthracnose is or you don't know how to identify lichen, you'll find all the common issues below to help you understand what's plaguing your tree and how to treat the problem.

Maple tree tar spot

Black spots and discoloration on leaves

Low (cosmetic)

Fungi

Late summer and autumn

Clean up leaf debris around the tree's base

Anthracnose

Leaves that curl around a dead-looking brown spot, tan or brown spots near the leaves' veins, cankers, dying young branches, and premature leaf loss

Low (cosmetic)

Fungi

Late spring to early summer; especially prevalent during wet periods

Keep tree from sitting in moisture; rake leaf debris; prune affected branches

Sooty mold

Powdery black mold covering leaves

Low (cosmetic)

Fungi, or plant and insect secretions

N/A

May require treatment of bugs that carry the fungus; can be brushed off

Lichens

Appearance is all over the place and can be dictated by region, weather, and other factors

Low (but can indicate more severe diseases)

Composite organism made of fungi and algae

N/A

Can usually just lift lichens off of the tree; may also prune branches that have it

Verticillium wilt

Wilting or yellowing leaves, often concentrated to one area or side of the tree

Moderate to severe (can kill tree)

Soil-bound fungi

July and August, particularly seen after a dry and hot summer

Plant resistant strains, remove the diseased tree, and/or fumigate the soil

Root rot

Symptoms vary wildly; often looks like mushrooms, can be cankers

Severe (usually lethal)

Mold

Wet seasons

Call an arborist immediately. The tree likely needs to be removed and destroyed.

Sapstreak

Dieback generally around the crown; external signs appear long after the tree has been infected

Severe (affects tree's innards)

Fungi

Late spring and early summer

Try to prevent the roots from getting damaged or wounded; some trees recover for no apparent reason

Phyllosticta mimima (maple leaf spot)

Ten to brown spots with a purple or red center

Low (cosmetic)

Fungi

Spring

Remove leaf debris. General tree maintenance. Plant resistant strains.

Powdery mildew

a fine powder-like mildew that covers leaves; white-ish in color

Low (cosmetic)

Fungi

Summer; thrives in greenhouse-like conditions (humid and hot)

You can brush the mildew off or apply horticultural oils.

Scorch

Dry, brown leaves

Low (cosmetic)

Weather conditions such as low moisture, high temperatures, and dry wind

Summer

Ensure that tree is well watered; apply mulch to help with water retention

Maple mosaic

White to yellow discoloration that's often kaleidoscopic looking

Low (cosmetic)

Virus

Summer (thought to be spread by the whitefly, whose population peaks in the summer)

There are no treatments. In fact, some people cultivate for this.

Pear thrips

Winged brown insects that are about the size of a nickel or smaller

Low (usually only damage foliage)

Insects

April through May

No known treatments.

Galls

Large number of varieties; usually look like black, red, brown, or green abnormalities such as a pimple or a needle

Low (cosmetic)

Mites

Seasons vary by type and mite

Some people have claimed to have success with pesticides and miticides, but this remains to be scientifically proven.

Two examples of tar leaf on a maple.

The maple tree tar spot is fairly easy to identify. It's caused by a fungal pathogen in the genus Rhytisma. While this affects maple trees in general, it especially targets Norway, silver, and sugar varieties. Tar spot will not kill your trees, but it's unsightly and can cause them to drop their leaves before the fall season.

The spots first appear as small yellow spots in June. Then, they progress to the black spots on the leaves you see above. Their size ranges from one-eighth of an inch to an inch or more in diameter on the Norway Maple. The spots can also appear on the seeds (samaras).

The fungus winters over on fallen leaves. If the leaves are not raked up in the fall, the fungal spores will reappear in the spring and spread to nearby trees. Treating the trees is usually not effective because the spores can travel from a neighbor's tree onto yours.

If your tree has these spots, which then causes leaves to curl in mid-July, it may have a different disease called Anthracnose.

Anthracnose on Maple Leaves

Charlotte Gerber

Anthracnose is commonly mistaken for tar spot. However, it inflicts much more extensive damage because it affects both the leaves and the branches. You'll find many more spots on the leaves that are typically smaller than the 1/8" tar spots.

This condition typically occurs when trees experience long periods of cold, wet weather. The affected areas may show small, dark spots and irregularly-shaped leaves with dead or brown areas. The leaves usually fall off in the early spring, followed by a second set of leaves which also die off. The branches can also develop cankers, which often strip them of their bark and kill them.

The disease continues when fungal spores over winter in dead leaves and infect trees during a prolonged wet spring. Once a tree is infected, the disease survives the winter in infected branches and then spread when the wind carries its spores to surrounding trees.

Anthracnose can be controlled by removing dead leaves from the base of your trees in the fall. You can also apply fungicide, but you may need a commercial application depending on the size and number of trees that may be affected. You can call your local Cooperative Extension office to see what fungicides are legal in your state.

While sooty mold mainly affects plants and trees that honeydew-secreting insects love, the mold can also effect maples.

Scot Nelson

Sooty mold feeds on the sticky honeydew left by aphids and scale insects, which can sometimes be found on maple trees. You'll know it's this mold if it rubs off easily on your fingers when you touch it.

The good news is that sooty mold won't kill your tree and can be easily treated. Try using a gardening mix that works to protect plants. Make sure to follow the instructions carefully and apply it at the base of the tree to ensure the roots absorb the mix ingredients. This method should also prevent reinfection for up to one year.

The University of Hawai'i has created an amazing PDF that explains the mold's lifecycle and is complete with many photos of the mold.

Lichens on a Maple Tree

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13 Common Maple Tree Problems and Diseases - Dengarden