Maple Tree - Knowledgebase Question

Concord, Vi
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Question by marycampbell
October 8, 2009
I have a Flaming maple 3 years old. I just added fertilizer spikes for the winter and noticed very black raised spots on most of the leaves; some holes also. Can you tell me what this is and how to fix it?
Thanks for your time

Answer from NGA
October 8, 2009
I can't tell from your description whether the raised areas are from blister gall mites (very short, slender raised areas on the leaves - usually red but can weather to a dark color), or from a fungal disease called tar spot. Both are common on maple leaves. Tar spot causes round to irregular black, tar-like spots on infected leaves. These spots are not noticeable until late summer. Tar spots of maple are caused by two species of the fungus Rhytisma which produce different symptoms. The first species, Rhytisma acerinum, produces black, tar-like spots about 1.25 cm or more in diameter on the upper surface of infected leaves. The second species, R. punctatum, produces patches of small, 1mm wide spots and is often called speckled tar spot. The thickened black spots are actually fungal tissue. Both fungi, R acerinum and R. punctatum survive between seasons on the fallen diseased leaves. In the spring, spores are produced within the black stroma and are carried by air currents to young maple leaves where they start new infections. Unlike many other foliar diseases, Rhytisma spp. do not continue to cause new infections throughout the summer. Infections first show up as yellow or pale green spots on the leaf surface in the early spring or summer. The black, raised tar-like spots of R. punctatum and R. acerinum develop within these spots by mid to late summer. Leaves, which are severely infected, may be shed. Although the spots are conspicuous and detract from the appearance of the leaves, tar spot seldom is so injurious to justify spraying with a fungicide. As symptoms develop late in the growing season, the overall health of trees is usually not affected. To reduce the amount of diseases overwintering, rake up fallen leaves in the autumn and destroy or remove them from the yard. Hope this answers all your questions about the black spots on your maple leaves.

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