How to Treat Japanese Maple Disease

Examine leaves, stems and branches for evidence of disease. Fungal diseases occur frequently when trees are exposed to prolonged wet, warm conditions. Common fungal diseases include anthracnose, botrytis, fusarium and verticillium. Antracnose is a common fungal infection that causes brown spots along the leaves' veins, splotches covering large areas of the leaves, or complete loss of leaves. Botrytis affects damaged or dead plant materials with a gray mold. Fusarium most frequently affects young trees, resulting in black or brown lesions in the stem and ultimately causing the young tree to fall over. Verticillium is among the most destructive disease -- it causes black or brown streaks in the branches and ultimately death of limbs or whole trees.

Treat Japanese maple trees with fungicide or leaf spot suppression treatments during the middle of spring. Follow the manufacturer's instructions for exact dosage of the chemical that you are using. Fungicides such as Daconil control leaf spot and other fungal infections and are mixed at a ratio of 1 or 2 tbsp. for every gallon of water. Repeat chemical treatment for infection during the early part of summer.

Monitor insect activity throughout the remainder of the season and early summer. Apply insecticide as needed. Insects such as aphids increase the tree's likelihood of developing fungal infection. Controlling insects encourages overall plant health while minimizing the chances of developing disease.

Fertilize trees with a balanced fertilizer during the fall. This boosts plant health, particularly after trees have been exposed to disease. Measure the tree trunk's diameter at the base of your Japanese maple and add approximately 1 cup of fertilizer for every inch. Water trees thoroughly, soaking approximately 12 to 18 inches of soil.

Prune trees during winter, removing all diseased or dead limbs in addition to shaping the tree to maintain the tree's form. Gather all leaves that have fallen prior to the Japanese maple leafing out in spring and discard. Fungal infections spread through spores that remain on dead leaves. Discard foliage to prevent spreading the disease or fungus to new and healthy leaves.