Sample size for quantification of Cercospora leaf spot in sweet pepper.
SUMMARY Cercospora leaf spot of sweet pepper (Capsicum annuum) caused by Cercospora capsici is an important disease occurring in the tropics. Due to the lack of standard methods to quantify this disease in field conditions, the objective of this study was to determine the ideal sample size for Cercospora leaf spot quantification in the field. Disease severity was determined in eight commercial sweet pepper (cv. All Big) fields located in the Agreste region of Pernambuco state (northeast Brazil). In each field, two diagonals (X) were established in a 0.5 ha area. Twenty-five plants were evaluated along each diagonal with the aid of an empiric scale to consider different sampling rates (3, 6, 9, 12 leaves/plant). The spatial pattern of the disease was estimated using Lloyd’s Index of Patchiness (LIP) and ideal sample sizes were calculated based on degrees of acceptable error (5, 10 and 20%). The spatial pattern was predominantly random and there was no correlation (P = 0.44) between the LIP values and sample size. Considering a sample of 3 leaves/plant with 10 and 20% rate of acceptable error, the mean ideal sample size was 103 and 26 plants, respectively, for each 0.5 ha of cultivated field.