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Ecology and Epidemiology

A Model for Weather-Based Forecasting of Anthracnose on Annual Bluegrass. T. K. Danneberger, Former graduate research assistant, Department of Botany and Plant Pathology, and the Pesticide Research Center, Michigan State University, East Lansing 48824, Present address of senior author: Department of Agronomy, Ohio State University, Columbus 43210; J. M. Vargas, Jr.(2), and A. L. Jones(3). (2)(3)Professors, Department of Botany and Plant Pathology, and the Pesticide Research Center, Michigan State University, East Lansing 48824. Phytopathology 74:448-451. Accepted for publication 3 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-448.

A multiple regression equation relating hours of leaf wetness and temperature to the incidence of disease incited in annual bluegrass by Colletotrichum graminicola was developed from 2 yr of field data. The model is ASI = 4.0233 - 0.2283 LW - 0.5308 T - 0.0013 LW2 + 0.0197 T2 + 0.0155 (LW T), in which ASI = anthracnose severity index, T = average daily temperature (C) for a 3-day period 10- 12 days preceding symptom expression and LW = average hours of leaf wetness per day for the same period. ASI values of 1, 2, 3, 4, 5, and 6 were equal to <10, 11- 20, 21- 30, 31- 40, 41- 50 and >51% of the turfgrass area diseased, respectively. The accuracy of the model was tested with data from three locations in 1982. The model successfully predicted 14 of 16 periods of disease increase when an ASI value of 2 was taken as the minimum conditions for infection. Average daily ASI values predicted from temperature and leaf wetness data were related to rate of disease increase according to the Gompertz transformation.