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Ecology and Epidemiology

Weather and Epidemics of Septoria Leaf Blotch of Wheat. Gregory Shaner, Associate Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907; Robert E. Finney, Research Associate, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907. Phytopathology 66:781-785. Accepted for publication 8 January 1976. DOI: 10.1094/Phyto-66-781.

Weather records were compared with severity of Septoria leaf blotch of wheat over a 20-year period at Lafayette, Indiana. In 3 years of “very severe” epidemics, in which all leaves of susceptible cultivars were killed prematurely, there were at least 40 days of rain from 1 April - 17 June, 8 days above average. A “severe” epidemic occurred when there were 34 days of rain if there was no excess of 2-day periods with minimum temperatures of 7 C or lower (34 such periods compared to an average of 26). It may be possible to forecast a “very severe” epidemic at the time flag leaves emerge by examining weather data from the previous 40 days (1 April - 10 May) and predicting weather for the next 35 days. A severe epidemic is likely to develop if past weather has been favorable, if the pathogen is well-established, and if the 30-day outlook is for much above-normal precipitation (17 or more days of rain from 11 May - 14 June).