variable_of entity attribute method_of Viruses infection severity - Estimation Observe relative or absolute area of plant tissue affected by virus disease and record the severity as a proportion or percentage of plant surface affected using visual five ordinal scale . Predominant severity per plot must be registered at least thrice : 8 to 10 weeks after planting, 4 to 6 weeks after first scoring and the last scoring at 4 to 6 weeks after the second scoring scale_of acronym