Leaf blight, caused by Curvularia eragrostidis, is the major foliar disease of yam in the Brazilian Northeast. Optimum sample size were determined in 15 commercial yam (cv. Da Costa) areas, located at Zona da Mata, Pernambuco State, Northeast of Brazil, aiming to orientate the disease assessment of yam leaf blight in field conditions. Disease severity was assessed in 100 plants by field in extracts of 5, 15, and 30 leaves by plant. The data set from each area were analyzed by a method that specified the level of acceptable error, determined by the mean coefficient of variation. The disease severity ranged between 0.41 and 22.34% and was negatively correlated (P=0.05) with the sample size. The increase of 15 to 30 leaves sampled for plant result small reduction in the total number of plants to be sampled differing of the observed when the increase was from 5 to 15 leaves. Based on data set and considering 10% of acceptable error, future surveys of yam leaf blight severity in Northeast fields should analyze 37 plants/ha and 15 leaves/plant.
Dioscorea cayennensis; Curvularia eragrostidis; sampling; disease assessment; epidemiology
