Japanese red maple trees have been intensively cultivated for more than three centuries. The trees are highly showy. They can be multistemmed shrubs, or small trees with single stems. The leaves of Japanese red maple trees are deeply lobed and are a bright purplish-red or red color, particularly during the spring and the autumn. The trees grow to between 15 and 25 feet tall. As with any trees, there are various possible diseases that could affect Japanese red maples.
Tar spot is a common disease for maple trees, include Japanese red maples. It is a fungal disease (from fungi of the Rhytisma genus). Tar spot isn't actually tar. However, the disease is known as tar spot due to one of its symptoms, which is the appearance of tar-like droplets on the surfaces of leaves. Tar spot is generally considered to be a minor condition. However, heavy infections of tar spot can lead to premature leaf drop. Leaves infected by tar spot need to be raked and destroyed, according to the Purdue Plant & Pest Diagnostic Laboratory.
Japanese red maples are one of the varieties of trees that are the most susceptible to manganese deficiency. These deficiencies are particularly common with maple trees that are cultivated over limestone soil that is highly alkaline. Some signs that a Japanese red maple is experiencing manganese deficiency include the leaves turning light green or yellow in color and the veins becoming deep green. Soil amendments can help manage manganese deficiency in the trees.
Leaf scorch is another highly common disease for Japanese red maple trees. Leaf scorch occurs due to environmental factors such as extended periods of heat, drought-induced stress and excessive winds. Inadequate or unhealthy root systems could also lead to the development of leaf scorch. Some signs of this condition include the leaves becoming brown and drying out in the areas between the veins. Dead or brown patches can also show up on leaf stems and younger branch and trunk tissues, as well. This condition can be prevented by pruning and proper fertilizing and watering.