Tree diseases

Posted 8/21/12

A variety of afflictions affect trees in the Upper Delaware River region, ranging from those caused by insects, like the hemlock wooly adelgid to others caused by fungi like anthracnose. “River …

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Tree diseases

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A variety of afflictions affect trees in the Upper Delaware River region, ranging from those caused by insects, like the hemlock wooly adelgid to others caused by fungi like anthracnose. “River Talk” reader, Star Hesse contacted us recently regarding the appearance of black blotches on the leaves of maple trees along Route 97 in Barryville, NY.

The photo she provided points to a fungal disease known as maple tar spot, which causes black spots of up to 1-1/2 inches in diameter which resemble tar. Fortunately, this infection does not normally pose a threat to the overall health of the tree, although it is unsightly and can cause early leaf drop, according to Cornell University’s Department of Plant Pathology and Plant-Microbe Biology.

Pale yellow spots typically appear in mid-June, then enlarge and intensify in color through summer. The fungi overwinter in leaf litter and just as new leaves unfold in spring, the surfaces of the tar spots split and release needle-like spores. Wind transports the spores to potential new hosts and the disease cycle can begin again.

The best means of breaking this cycle is to rake up and destroy the affected leaves, which may take several years and repeated effort to achieve, particularly if nearby trees are afflicted. Fungicides are available, but the disease is difficult to control. Cornell notes that it has become widespread across much of New York State.

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