Brown Spots On Maple Leaves

If you’re seeing brown spots on maple leaves, you’re likely dealing with a common fungal leaf disease. These unsightly spots can worry any gardener, but understanding the cause is the first step to managing it.

This guide will help you identify the specific fungus, explain why it happens, and show you how to treat and prevent it. With some simple steps, you can help your maple tree regain its health and beauty.

Several different fungi can cause those troubling brown spots. The most common culprits are tar spot, anthracnose, and maple leaf blister. Each creates a slightly different kind of spot, so identification is key.

While these diseases look alarming, they are rarely fatal to established, healthy trees. The main impact is aesthetic, but severe, repeated infections can weaken a tree over time by reducing its ability to photosynthesize.

Identifying the Fungus on Your Tree

Look closely at the spots. Their size, shape, and timing offer big clues.

Tar Spot: Starts as small pale yellow spots in spring. By late summer, they develop into large, shiny, black, raised spots that look like drops of tar. The surrounding leaf area may turn yellow.
Anthracnose: Causes irregular brown or black spots that often follow leaf veins. Leaves may look scorched or ragged. Infected leaves often curl and drop prematurely, especially in wet springs.
Maple Leaf Blister: Appears as large, brown, circular blotches or blisters on the upper leaf surface. The underside of the blister may have a lighter, fuzzy appearance.

Why Did This Happen to My Tree?

Fungal diseases thrive under specific conditions. The primary driver is moisture. Cool, wet springs are perfect for spore germination and infection.

Spores overwinter in fallen, infected leaves and in tree bark crevices. In spring, wind and rain splash these spores onto new, emerging leaves. If the leaves stay wet for long periods, the fungus infects them and the spots develop.

Step-by-Step Treatment and Control

For most mature trees, fungicide sprays are not recommended or practical. The focus should be on cultural and sanitary practices.

Rake and Destroy Leaves: This is the single most important step. In autumn, carefully rake up all fallen leaves from under the tree. Bag them and send them to the landfill—do not compost them, as most home compost piles don’t get hot enough to kill the fungal spores.
Prune for Airflow: In late winter, prune any crowded or crossing branches. This improves air circulation through the canopy, allowing leaves to dry faster after rain or dew. Fungi struggle to infect dry leaves.
Water Wisely: If you water your tree, do it at the base. Avoid overhead sprinklers that wet the foliage. Water in the morning so any accidental splashes dry quickly.
Consider Fungicides (For Young or High-Value Trees): If a young tree is severely affected year after year, a preventative fungicide may be warranted. Apply a product labeled for maple fungal diseases (like chlorothalonil or mancozeb) in early spring as buds open, and repeat as the label directs. Always follow label instructions exactly.

Prevention is the Best Medicine

Stopping the cycle of infection is easier than curing an outbreak. Since the fungus needs wet leaves and old debris, your prevention plan targets those.

Keep the area under the tree clean. Maintain good tree health through proper mulching and fertilization, so it can better withstand minor infections. A stressed tree is more suseptible to disease.

Common Questions About Maple Leaf Diseases

Will the brown spots kill my maple tree?
No, it is very uncommon for these foliar diseases to kill a healthy, mature maple tree. They primarily cause cosmetic damage and early leaf drop. The tree’s long-term health is usally not threatened.

Should I spray my tree if I see spots?
By the time you see the brown spots in mid to late summer, it is too late to spray for that year. Fungicides are only effective as a preventative treatment, applied in spring as leaves emerge.

Can I compost the infected leaves?
It is not recommended. To safely compost fungal disease material, you need a hot, managed compost system that reaches high sustained temperatures. Most backyard piles don’t achieve this, allowing the spores to survive and spread.

Are some maple varieties more resistant?
Yes. For example, some Japanese maple cultivars are more suseptible to leaf issues. Red and silver maples tend to get tar spot more often. Norway maples show some resistance. When planting new trees, research disease-resistant varieties for your area.

Does weather affect these diseases?
Absolutely. A cool, wet spring leads to a severe outbreak. A hot, dry spring can significently reduce the incidence of disease. This is why the problem can be bad one year and mild the next.

When to Call a Professional Arborist

Most cases of leaf spot can be managed by a diligent gardener. However, seek professional advice if:

A young tree is repeatedly defoliated every year, stunting its growth.
You notice other symptoms beyond leaf spots, like dieback in the branches, oozing cankers on the trunk, or a general, rapid decline in the tree’s health.
The tree is very large, making leaf cleanup or assessment difficult. An arborist can provide a full health evaluation.

Remember, brown spots on maple leaves are a common issue. While they can be dissapointing to see, they are a manageable part of growing these beautiful trees. Your consistent care in cleaning up leaf litter and promoting good airflow will make a huge difference for next season’s foliage.

By taking these proactive steps, you give your maple the best chance to thrive. Healthy trees are more resilient, and with the right practices, you can minimize the impact of these common fungal leaf diseases for years to come.