What Kind of Maple Trees Are Getting Early Black Spots on Their Leaves?

Frost Injury

• All species of maple are susceptible to developing black spots on their leaves. This can be caused by one or more of several different diseases or disorders that afflict the foliage of the maple. Environmentally, young, tender leaves are especially prone to frost damage, as a late spring frost can cause them to blacken or brown, with the edges curling. Maple leaves that are not killed by this injury may be left with jagged holes resembling that of a feeding binge by insects.

Tar Spot

• Tar spots are a problematic fungal disease that afflicts different species and varieties of maple. The fungi --- of the genus Rhytisma --- produce raised black spots, resembling globs of tar, on the upper surface of the leaf. The disease normally appears early in June as small, yellow spots less than 1/8 inch in diameter. The yellow hue deepens over the course of the season, with a black spot appearing inside the yellow one.

Tar Spot Management

• Leaves infected with tar spot drop to the ground in the fall and then over-winter before spreading fungi spores through the air as spring beckons, thus infecting a new generation of leaves. The best management of this disorder is to ensure the removal and destruction of all infected leaves in the autumn. Still, infected trees in adjacent settings can also spread the disease, so application of a fungicide may be necessary. However, even this technique may not suffice, as especially large trees are difficult to completely envelop with a fungicide.

Phyllosticta Leaf Spot

• Phyllosticta leaf spot (Phyllosticta minima) regularly infests red, silver, Japanese and Amur maples. Circular, tan-colored spots develop with red or purple borders. These spots eventually grow a black, fruiting body inside the circle of the wound. The damage is typically only aesthetic, and application of fungicide is rarely necessary. However, leaves may drop in early to midsummer. Infection is normally most severe in the lower third of the tree, where more moisture allows for the easy spread of spores.