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Fungal Diseases of Maples

Posted: June 10, 2014

The Extension offices have been receiving calls about black leaf spots and leaf drop on maples. Some of you are wondering if this is detrimental or worthy of treatment. Although the only way to be sure is to submit samples to the disease clinic, there are some fungal pathogens that are likely culprits at this point in the season.
Photo: Bruce Watt, University of Maine, Bugwood.org leaf blister Taphrina spp. red maple Acer rubrum

Photo: Bruce Watt, University of Maine, Bugwood.org leaf blister Taphrina spp. red maple Acer rubrum

One we have received reports about is maple leaf blister, a fungal disease that infects leaves early in the season. Symptoms reported include black, irregular leaf spots (with the appearance of blisters) that occurred on the first leaves. In some cases the severely infected leaves have dropped and the plants have pushed new leaves that are unaffected.

Much more common is anthracnose, and we’ve also seen plenty of that this year. Anthracnose can cause large dark-brown blotches along the veins and between them; and leaves can be puckered or deformed. Anthracnose infections are common on lower limbs and on branches close to the trunk so that from a distance the trees look like the lower and inner branches have fewer and smaller leaves than the outer and upper branches.

Anthracnose on maple
Photo: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org anthracnose Discula spp. maple Acer spp.

Both diseases can occur on the same trees at the same time, making them look worse. There are no effective treatments at this time—the infections occurred during cool wet periods we experienced early in the year.

Penn State Plant Disease Clinic

Anthracnose on Shade Trees

Maple Leaf Blister