Diseases of the Japanese Red Maple Tree

Overview

Red Japanese maples (Acer palmatum) are prized ornamentals, 6–30 ft tall, with varied growth habits and leaf colors. Generally disease- and pest-resistant, but environmental stress or poor cultivation can trigger issues.

Key Diseases

Leaf Scorch

Caused by high heat, drought, wind, or inadequate roots. Leaves brown and desiccate between veins. Young branch tissues, leaf stems, and trunk tissue may also show brown/dead patches.

Manganese Deficiency (Chlorosis)

Leaves turn yellow/pale green with dark green veins. Often due to soil pH blocking uptake, not lack of manganese. Treat with soil amendments.

Tar Spot

Fungal infection (Rhytisma spp.) causing black, tar-like spots on leaf tops. Starts yellow in early summer, turns black by late summer. Unsightly but rarely life-threatening. Rake and destroy infected leaves—do not compost.

Management

Reduce stress: water deeply during drought, mulch, avoid root disturbance. Test soil pH and amend for nutrient availability. Practice good sanitation—remove fallen diseased leaves promptly.