Leaf Spots on a Japanese Maple Bloodgood Tree

Phyllosticta Leaf Spot

• The Japanese maple Bloodgood is among the maples especially susceptible to Phyllosticta leaf spot, a disease brought on by dissemination of the fungus Phyllosticta minima. The degree to which the leaves are affected varies, ranging from a few spots on each leaf to more severe cases, resulting in the early dropping of those leaves from the tree. Leaves that routinely receive moisture are the most affected. A black, fruiting structure called pycnidia forms in the middle of the leaf.

Phyllosticta Management

• Gardeners will normally notice the most extreme infection on the bottom one-third of the tree, a location likely to receive more moisture and thus be more susceptible to the spread of the fungi spores. The disease overwinters on leaves that have fallen to the ground, so removal and destruction of these leaves to prevent re-infestation in the spring is vital. The application of a fungicide may be helpful, but they act primarily as protectants and do little to stop the disease once symptoms have occurred.

Tar Spot

• Leaf spots on a Japanese maple Bloodgood tree also may be the result of a fungus of the Rhytisma genus tar spots. This disorder first appears as pale, yellow spots measuring approximately 1/8 inch in diameter, normally first popping up around June. The yellow spot begins to take on a more intense yellow hue as the growing season continues, eventually allowing a dark black spot to grow in the middle of each spotting. This spot grows in both diameter and thickness.

Tar Spot Management

• The tar spot fungus also overwinters on leaves that have fallen to the ground and then jumps back to life with the coming of spring, ready to infest a new selection of young, tender leaves. Raking away and destroying the leaves in the fall is an important management technique for this disease, but the tar spot fungus easily transmits from adjacent trees and neighborhoods, so severe cases may demand the application of a fungicide.