Soybean target spot, caused by Corynespora cassiicola, is found in practically all the soybean growing regions in Brazil and it can cause economic losses. The objective of this work was to elaborate and validate a diagrammatic scale to evaluate soybean target spot severity. Soybean leaflets with disease symptoms were collected and severity was measured, determining the minimum and maximum limits and the intermediate levels of the scale, according to Weber-Fechner's stimulus-response law. The elaborated scale had seven levels: 1, 2, 5, 9, 19, 33 and 52%. The validation was performed by eight persons without experience with this disease quantification, who estimated the severity of 40 leaflets with different levels of target spot severity, with and without the use of the scale. The use of a diagrammatic scale resulted in higher accuracy and precision of the estimations performed, meaning that this can be considered a quick and easy tool to help evaluate soybean target spot severity.
Glycine max; Corynespora cassiicola; disease assessment
