Unusual Epidemic of Tar Spot on Norway Maple in Upstate New York. George W. Hudler, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Mark T. Banik, and Steven G. Miller. Department of Plant Pathology, Cornell University, Ithaca, NY 14853, and Oneida County Cooperative Extension, Oriskany, NY 13424. Plant Dis. 71:65-68. Accepted for publication 3 June 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0065.

Tar spot, caused by Rhytisma spp., has caused serious defoliation of Norway maples (Acer platanoides) in several upstate New York communities in recent years. Green- and purple-leaved varieties of all sizes and ages have been attacked; many have been completely defoliated by mid-August. Although R. acerinum is the only species of Rhytisma reported on Norway maple, the pathogen described herein differs from R. acerinum (common on red and silver maples in New York) in size and morphology of stromata, production of asexual spores, and growth habit in culture. The disease was controlled with benomyl, mancozeb, or triadimefon sprayed to runoff at budbreak and twice thereafter at 15-day intervals.