Japanese Maple Leaves With Yellow Spots
- Phyllosticta leaf spot, a fungal disease, causes circular, tan leaf spots with purple or reddish borders. Eventually, black fruiting bodies develop in rings within the spots. Phyllosticta leaf spot is controlled by proper cultural practices. The fungus can overwinter on fallen leaves, so remove these each fall. The fungus thrives in damp, dense growth. Prune out branches to improve air circulation and avoid using overhead irrigation. Phyllosticta infections typically do not require fungicide treatment.
- Tar spots first appear as yellowish spots on the upper surface of leaves in late spring or early summer. Later in the growing season a black, tar-like tissue occurs within the spots. Leaf drop may occur but fungicide is usually unnecessary. Good cultural practices can keep tar spot under control.
- A Japanese maple may experience scorch as a result of high temperatures and winds or because the tree's root system is diseased or inadequate. A scorched tree develops light brown or tan dead areas between leaf veins. These scorch symptoms may be located on only one side of the tree or all parts of the tree. If the tree is scorching from drought, watering will alleviate the scorch.
- A nutrient-deficient Japanese maple will develop yellow leaves while veins remain green. Japanese maples most commonly suffer from a manganese deficiency, which can be corrected by implanting manganese capsules in the trunk. For an accurate and complete diagnosis of a nutrient deficiency, conduct a soil test that includes a pH test. Herbicide exposure will produce symptoms similar to a nutrient deficiency.