The assessment of severity with chronological development of disease of mesta (Hibiscus cannabinus, cv. HC-583) on a particular diseased plant was studied. Based on the symptomatology and intensity of diseases caused by Begomovirus an empirical formula was developed. A methodology for assessing the disease intensity of yellow vein mosaic disease of mesta grown under natural field condition was proposed and it was validated by comparing with infected plants grown under field as well as glasshouse conditions. Quantitative assessment of the disease indicated that the disease index value at different stages of pathogenesis varied from 1.82 to 49.44 under field condition whereas the same varied from 2.78 to 50.83 under glasshouse condition. Mortality of infected leaves was noticed when the index value reached maximum. With the present methodology scoring of gradual development of disease has become possible for a particular plant and even for an individual leaf of a particular cultivar.