Subject : Japanese maple leaf Discoloration 

Hello Brian

Thank you so much for reaching out to the UNH Extension Infoline.

Following up on your recent inquiry on Oct 15/2025 about your Japanese Maple concern, please see valuable information that will effectively guide you through this issue and lead you to potential solution. Your situation matters to us, and I am confident that with the right guidance we can provide you with solution.

Please reach out if you have any further questions.

The UNH Extension Infoline Team,

Master Gardener volunteer, Haim.

General information 

Although it is hard to diagnose plant/tree from photos, please see some suggestions and information

Japanese maple leaf discoloration is often caused by leaf scorch from excessive sun, under or overwatering, or fungal diseases like leaf spot and anthracnose. Proper watering, appropriate sun exposure (especially afternoon shade), good air circulation, and sanitation are key to prevention and management.

Common causes of discoloration

Leaf Scorch:

Browning or crisping of the leaf edges, especially in hot, dry weather. This happens when the tree is overexposed to intense sun.

Watering Issues:

Underwatering: Can cause leaves to dry out, brown, and curl.

Overwatering: Can lead to root rot, causing yellowing or browning leaves and wilting, even with wet soil.

Fungal Diseases:

Phyllosticta Leaf Spot: Causes small, circular brown or black spots, sometimes with a purplish border.

Anthracnose: A fungal disease that creates dark, sunken lesions on leaves, stems, and branches.

Powdery Mildew: A white, dusty coating on the leaves that can weaken the tree if severe.

Natural Adaptation:

Some discoloration, like a change to reddish tones, can be a natural response to light conditions as the tree adapts to its environment.

How to manage and prevent discoloration

Water Properly:

Water deeply but infrequently, allowing the top inch or two of soil to dry out between waterings.

Ensure the soil has good drainage and water the plant at its base to keep the foliage dry.

Improve Air Circulation:

Prune the tree to allow for better airflow and light penetration.

Avoid overcrowding other plants.

Practice Good Sanitation:

Rake and remove fallen leaves from around the base of the tree, especially in the fall, to reduce the overwintering habitat for fungi.

Treat Fungal Infections:

Remove affected leaves to prevent the spread of disease.

If infections are severe or persistent, apply a preventative or curative fungicide labeled for your tree and disease.

For powdery mildew, no treatment is needed if it appears late in the season, but preventative measures can reduce its return.

Website to visit :

https://extension.umaine.edu/gardening/2021/07/12/japenese-maple-tree/

https://extension.uconn.edu/publication/why-are-maple-leaves-turning-brown-and-falling-early/