Weeping laceleaf Japanese maple trees, also known as dissectum Japanese maples, are characterized by the lacy appearance of their foliage, a nearly shrub-like growth habit and unusual coloration. Japanese maples can be staked to grow or appear taller but still retain their weeping habit. The Japanese maple is most commonly affected by only a handful of problems or pests.
Scorch on Japanese maples appears as light brown or dead areas between veins on leaves. Scorch may appear only on part of the tree if the scorch is the result of sun or wind. Scorch can be caused by wind coupled with high temperatures, inadequate available water or a diseased or suffering root system. If the scorch is the result of drought, watering will improve the scorch. Trees with diseased root systems will not improve with increased watering. The tree should be planted in filtered shade and out of drying winds if those factors cause scorch.
A nutrient-deficient Japanese maple will have yellowing leaves with darker veins. Japanese maples most commonly suffer from a manganese deficiency, which can be corrected by implanting manganese capsules in the trunks. If a nutrient deficiency is suspected, conduct a soil test to determine the best course of action. Plants suffering from herbicide exposure may suffer similarly.
If the tree is planted in a wet site, it is more susceptible to Phytophthora root rot and root collar canker. Trees will wilt, suffer from die-back and may eventually die. Soil nematodes are small worms that feed on the maple roots, restricting the tree's water uptake and causing wilting and die-back. Soil nematode activity also makes trees more susceptible to verticillium wilt disease. Verticillium wilt results in leaf wilting and branch or entire tree death.
Leaf Spot Diseases
Japanese maple is susceptible to multiple leaf spot diseases like Phyllosticta leaf spot, anthracnose and Pseudomonas tip blight. As long as the tree is healthy, leaf spots are typically only an aesthetic concern. Most can be treated, if necessary, with a fungicide application.
Japanese maples may be infested by aphids, which excrete honeydew and can cause leaf drop if the population is large. Scales, like the cottony maple scale, cluster on the tree branches and can be controlled with horticultural oil sprays. Borers may also become an issue if a tree is not healthy. The specific borer attacking the tree should be identified in order to determine the proper treatment. Insects do not usually cause severe damage on healthy trees, so proper care is a key aspect of preventing infestations.