I found a new fungi I have never had on a maple tree.
Black spots formed on the upper leaf surfaces. The disease is called "tar spots" because their appearance so closely resemble droplets of tar on leaf surfaces. Tar spot alone is rarely serious enough to threaten the health of trees, but sometimes there can be so many spots that the tree becomes unsightly. Heavy infections can also cause early leaf drop — a circumstance that causes the greatest consternation to homeowners because lawns are littered and must be raked before autumn officially arrives.
The first symptoms of infection by tar spot fungus usually show up in mid-June as small, pale yellow spots, less than an eighth of an inch in diameter. The spots enlarge and their yellow color intensifies as the season progresses.
On red maple and silver maple, a black spot usually develops in each yellow spot by mid-July to early August. The black spot grows in diameter and thickness until, by late summer it looks like a spot of tar. The surface of the spot may have a pattern of wavy indentations or ripples.
Another form of tar spot affects striped and Norway maples. On these trees 20 to 50 small spots, each no larger than a pin-head, appear in late July or early August.
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On the striped maple, the spots don't enlarge much after they first appear. But on the Norway maple, the spots grow and eventually coalesce to a black mass up to 1.5 inches in diameter. The surface may be slightly roughened to smooth, but will not be rippled.
The fungi that cause tar spots can live through the winter on infected leaves that fall to the ground. The following spring, just as new leaves are unfolding, the fungal tissue in the leaves on the ground ripens. The surfaces of the spots split, and minute, needlelike spores escape and are carried by wind. If they land on a susceptible host they may germinate, penetrate the leaf tissue, and start a new disease cycle.
Current research indicates that the fungus doesn't cause long-term damage to the host. The most effective management practice in a home lawn situation is to rake and destroy leaves in the fall. This will reduce the number of overwintering "spots" (containing the fungal reproductive structures) that can produce spores the following spring.
Mulching leaves will suffice to destroy many of the spots before they mature, but the mulch pile should be covered or turned before new leaves begin to emerge in spring. Application of fungicides are possible when high levels of infection become unacceptable, but control of the disease is difficult. Complete coverage of leaf tissue is needed for success and this can be difficult on mature maples.
If you live in a neighborhood that has the disease and homeowners aren't using fungicides or proper sanitation, spraying the tree won't help. If you want to use a pesticide, consult a licensed tree care professional. If the maple leaves crinkle and turn brown in June or July then it is possible it may another common disease called anthracnose. Consult your local Extension office.
