Many crepe myrtles are prone to powdery mildew and leaf spot. Powdery mildew is identified by the presence of scales on the flowers and white patches on the leaves and shoots of the plant, with the problem getting worse as the growing season progresses. Leaf spot results in loss of all or most of the plant's leaves. The first sign of the disease is brown spots on the leavesContinue Reading
Many newer breeds of crepe myrtle are resistant to powdery mildew. Older breeds that are affected by the disease are treated by increasing the amount of air circulation and sunlight. Fungicides labeled for use on powdery mildew can be applied once the leaves fully expand. The tree should be dosed once a month until the flowers begin to bloom.
Leaf spot disease begins to appear in June or July on lower leaves. The spores travel higher on the plant until all the leaves begin to turn yellow and red and drop from the tree by late summer. Warm weather and stagnant air help the spores grow and spread. Good air circulation helps the crepe myrtle's leaves dry quickly, removing a breeding ground for the spores. Gardeners must apply a fungicide once a week when the weather turns warm to prevent leaf spot disease.Learn more about Trees & Bushes