Several disease assessments are available but most of these are more qualitative than quantitative. These qualitative disease indices are derived from arbitrary ratings ranging from zero to a number depending of the rating. Some of the ratings are subjective and depend on the prejudice of the researcher. The present disease index (DI=1.36 + 0.04W) is not only reliable simple but also quantitative and does not introduce bias in disease assessment. It is therefore recommended for leaf disease assessment.