Assessment of Andean bean diseases using visual keys

Pictorial keys are given for the visual assessment of damage to bean ( Phaseolus vulgaris ) leaves of diseases found in the Colombian Andes. There are keys for anthracnose, rust, ascochyta blight, web blight and angular leaf spot, and also for necrotic tissue and damage to leaves by adult chrysomelid beetles. Unusual features of the keys are discussed. Their evaluation by a group of untrained assessors demonstrated that the average deviation from the correct values was -0.171 of one unit on a scale of 0 to 9. Statistically significant differences existed between assessors, and there were interactions with other variables. These findings suggest that care should be taken to minimize the effects of likely differences among assessors, and the implications of this are discussed.