A Loss Model for Crops

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Abstract
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 2 disease-host systems [Cercospora leaf spot of peanut (Arachis hypogaea) caused by C. arachidicola and C. personata, and early blight of potato (Solanum %tuberosum) caused by Alternaria solani] 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 to an analysis of the model parameters.