Cercospora leaf spot caused by Cercospora canescens and Pseudocercospora cruenta is an important disease of cowpea (Vigna unguiculata) in Brazil. Due to the inexistence of standard methods for the assessment of this disease, a diagrammatic scale was developed with 1, 2, 4, 8, 16, 32, 64 and 82% of diseased leaf area. The diagrammatic scale was validated by 10 raters using 50 cowpea leaflets with different levels of severity previously measured by the software Assess®. The accuracy, precision and reproducibility of the estimative of each rater were determined by simple linear regression between actual and estimated severity, with and without the use of the scale. With the scale raters obtained better levels of accuracy and precision, with absolute errors concentrating around 10%. Raters showed high repeatability (94%) and reproducibility ( 90% in 82.3% of the cases) of the estimates by using the scale. The proposed diagrammatic key is suitable for the evaluation of Cercospora leaf spot severity in cowpea.
Vigna unguiculata; Cercospora canescens; Pseudocercospora cruenta; phytopatometry
