Occurrence of Septoria nodorum Blotch and S. tritici Blotch in Michigan Winter Wheat. L. P. Hart, Assistant Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. D. W. Fulbright, Assistant Professor, and J. L. Clayton and A. V. Ravenscroft, Senior Research Associates, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. Plant Dis. 68:418-420. Accepted for publication 30 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-418.

Winter wheat in commercial fields was surveyed in 1982 and 1983 for Septoria blotch disease. Distinct differences in the occurrence of Mycosphaerella graminicola and Leptosphaeria nodorum were observed between the two years. M. graminicola and L. nodorum occurred frequently during the early growth stages in 1982, but by heading, M. graminicola was rarely observed on the flag leaves. Glume and most flag leaf infections were caused entirely by L. nodorum in 1982. In 1983, M. graminicola occurred more frequently throughout the growing season than L. nodorum and was common on flag leaves. The differences between the occurrence of M. graminicola and L. nodorum in 1982 and 1983 indicate an important role for the environment as a factor in pathogen selection, infection, and early-season severity.