Japanese maple trees, prized for their vivid fall and spring leaf color, are susceptible to a variety of diseases. Identifying diseases on Japanese maple trees will allow you to recognize disease symptoms, treat any present illness and prevent future health problems so your trees can maintain growth and remain vigorous. In many cases, fungicides are effective at treating and preventing these diseases and pests.
During late spring and early summer the Japanese maple may exhibit some of the following symptoms: a thinner canopy, leaf spots with angular edges, areas of dead leaf tissue, a die-back of twigs and cankers on small branches, according to the University of Tennessee Agricultural Extension Service. All are signs of anthracnose, a fungi that affects Japanese maples and causes defoliation that leads to weakness. When left untreated, anthracnose is a fatal to Japanese maple trees. To prevent the spread of anthracnose, rake and destroy or compost infected fallen leaves. Maintain the vigorous health of your Japanese maple through fertilization, pruning, watering and pest control to increase tolerance to anthracnose.
Powdery mildew is a fungal infection that causes disease on Japanese maples. Powder-like mildew forms like a blanket on the tree in gray-white lesions. Powdery mildew is rarely a serious disease on Japanese maples. The disease probably is more prevalent in moist climates, as powdery mildew needs humidity to flourish. Maintain the vigor of your tree to prevent powdery mildew infection and destroy infected fallen leaves.
Various leaf spot diseases caused by fungal infection (like Phyllosticta and Septoria fungi) are found on Japanese maples, causing visible spots on the surface of leaves. Often triggered by a wet spring season, this fungal infection may spread on your Japanese maple tree, generally causing cosmetic injury, according to the University of Tennessee Agricultural Extension Service. Illness is generally not serious but may cause premature defoliation.
Leaf scorch is a disease on Japanese maple trees that causes leaves to appear burned; darker areas of brown and black become visible on the surface of the leaves. Leaf scorch is caused by a bacterium-like pathogen that is spread by leaf hoppers. Leaf hoppers carry and transmit the bacterium. Leaf scorch lesions will be the first symptom to appear, followed by diminished health and a loss of leaves in which foliage remains only on large branches close to the interior crown of the Japanese maple tree. There is no effective treatment for bacterial leaf scorch, though antibiotic injections can prolong the life of the tree.