Mycosphaerella Leaf Spot of Black Walnut. Kenneth J. Kessler, Jr., Principal Plant Pathologist, USDA Forest Service, North Central Forest Experiment Station, Forestry Sciences Laboratory, Carbondale, IL 62901. Plant Dis. 69:1092-1094. Accepted for publication 30 June 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-1092.

A leaf spot disease of black walnut (Juglans nigra) that causes premature defoliation in plantations has been found in Illinois, Indiana, Iowa, and North Carolina. The causal fungus is Mycosphaerella juglandis, heretofore known by the name of its anamorph, Cylindrosporium juglandis. Symptoms are described; etiology and the causal organism’s characteristics are reviewed. Many Juglans species and hybrids are susceptible to infection by M. juglandis, Carya ovata and C. illinoensis, also Juglandaceae, are resistant. The disease can be controlled on black walnut by four spray applications of benomyl.