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Effect of Moisture on Septoria tritici Blotch Development on Wheat in the Field. Dale E. Hess, Graduate research assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Gregory Shaner, Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 77:220-226. Accepted for publication 8 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-220.

The relationship between occurrence and duration of moisture in the field and development of Septoria tritici blotch (caused by Mycosphaerella graminicola) on wheat was investigated. In a wet year (1983), when weather favored natural disease development and release of spores from pycnidia within lesions, moist period duration was more important than inoculation in enhancing disease increase. In a dry year (1984), when conditions were unfavorable for disease development and spore dispersal, moist periods after inoculation enhanced disease spread more than equivalent moist periods without inoculation. By assessing disease on individual tagged plants at 2- to 4-day intervals, we were able to associate disease increase with periods of rainfall 1416 days earlier. Disease severities on the spike, flag leaf, and penultimate leaf of individual plants at the early dough stage of growth reflected the vertical nature of disease spread and were related to reduction in thousand seed weight and crop yield. The inoculation technique developed was successful even in weather ill-suited to natural infection.