Citrus black spot is a disease caused by Guignardia citricarpa which produces lesions in fruits of commercial varieties of sweet orange, causing premature fall of fruits, decreasing the yield and leading to depreciation of the fresh fruit market. The aim of this study was to develop and validate a model of climate favorability for citrus black spot related to the occurrence of the disease symptoms in the state of São Paulo (SP). An empirical system was developed based on a data bank of the disease occurrence and the climate conditions in the field in the municipalities of Barretos/SP and Gavião Peixoto/SP, during the 2007/2008 and 2008/2009 crop cycles. The sweet orange variety used in the experiments was 'Valencia' grafted onto 'Rangpur' lime aged 10 years. For black spot incidence, the percentage of fruits with symptoms in the plant was evaluated, and for severity, the percentage of skin lesions per fruit was assessed. In the regression analysis, the climate variables and the data related to the disease intensity in Barretos were selected in the 'stepwise' procedure. The best regression equations were selected by the coefficient of determination (R²) and by the significance of regression in the F test (P <0.05 and P <0.01), which resulted in the equation Y = -502.43 + 9.61 X10 + 4.78 X30 + 0.54 X46 - 7.9 X50, where Y = Favorability Index, X10 is the average temperature, X30 is the average relative humidity, X46 is the leaf wetness and X50 is the average temperature during leaf wetness, determined with data from 7-day intervals. Validation was carried out in the field in Gavião Peixoto Municipality during the 2008/2009 crop cycle, correlating the incidence and severity observed in the experiment with the predicted data that were determined by the equation, and the correlation was positive for the disease incidence with R² = 0.87.
Citrus; Guignardia citricarpa; Climate favorability
