Japanese maple trees come in a wide variety of cultivars that are generally disease-resistant and can grow and flourish in a variety of climates. However, when problems with Japanese maple tree disease do strike, you need to be able to recognize the signs and symptoms right away in order to develop a plan for treatment. Knowing what to look for and how to react can keep your glorious Japanese maple blooming beautifully for years to come.
Japanese maple tree diseases come in two main forms: blight and fungal infections. There are two types of blight: anthracnose and pseudomonas tip blight. Three types of fungi routinely present problems for Japanese maple trees. These fungi are Botrytis, Fusarium and Verticillium.
One of the first things you may spot if your Japanese maple has a disease problem is an outbreak of small, round, red or purple spots on the leaves of the tree. You may also notice wilting leaves and gray, white or black growth on the tree itself. Leaves and small branches and shoots may also turn dark and die. Look closely at the stems of the leaves and the base of the branches and even the trunk for small, black lesions and even brown or black streaks that are visible just under or even through the bark of the tree.
Diagnosing the Problem
Once you have taken note of the symptoms of your tree, you can start to remedy the situation. If your leaves are spotty, then generally this is caused by one of the two types of Japanese maple tree blight. On the other hand, black lesions at the base of branches, leaves or even the trunk tend to indicate an issue with the fungus Fusarium. This is particularly likely if the tree is relatively young. Verticillium causes the black streaks, while Botrytis, also called gray mold, is the source of black or gray growths on the body of the plant.
If you have fungal issues, then they can be treated by restricting watering--only water when the ground is dry and then water deeply so that you do not have to do so again for some time--and with fungicides. You must be very careful if you attempt to starve the fungi by withholding water because Japanese maples are very susceptible to water shortages. Whether you are dealing with fungi or blight, be sure to use sterilized pruning equipment to remove all affected parts of the tree. Dispose of the pieces in a garbage bag rather than dropping them on the ground or in a compost pile. Blight can usually be controlled by removal and then by increasing air circulation using fans.
Of course, the best way to keep your Japanese maple tree healthy is to prevent it from contracting disease in the first place. Always water in the morning to avoid wet foliage in the afternoons. Water regularly, but do not over-water or water in small amounts every day or throughout the course of a day. If you do this, you are creating a moist environment that is ideal for fungi and disease rather than for your maple.
A new disease called sapstreak disease is making an appearance on the Japanese maple scene. It is unknown exactly what types of problems this disease will cause in the long run, but in the short term it leaves the wood of the maple discolored in long streaks that look like sap has run down the trunk.