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Disease Detection and Losses

A Loss Model for Crops. L. V. Madden, Former graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, Current address of the senior author: Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; S. P. Pennypacker(2), C. E. Antle(3), and C. H. Kingsolver(4). (2)Associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (3)Professor, Department of Statistics, The Pennsylvania State University, University Park 16802; (4)Adjunct professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 71:685-689. Accepted for publication 20 November 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-71-685.

Contemporary models for describing and predicting yield reduction caused by plant diseases were selected, usually with ordinary least-squares regression, to best fit the data and not necessarily to represent biological reality. A generalized nonlinear model with inherent flexibility was developed to characterize the relationship between crop loss and plant disease. In addition to providing loss predictions at various levels of disease, the model incorporates: a threshold disease level below which no loss occurs, a maximum level of loss that may occur prior to the maximum amount of disease, and a large family of curve shapes to depict disease-loss relationships. The model was fit to simulated and actual loss data sets. The model numerically approximated the critical-point loss models reported in the literature and also described loss for two disease-host systems over a 2-yr period. The availability of a single model has the advantage that losses caused by different diseases on different crops can be compared directly by an analysis of the model parameters.