USING COLOR IMAGE-ANALYSIS FOR QUANTITATIVE ASSESSMENT OF POWDERY MILDEW ON CUCUMBER

Visual assessment, black and white image analysis and colour image ana lysis of the severity of powdery mildew (Sphaerotheca fuliginea) infec tion on leaves of cucumber (Cucumis sativus) were compared. The extent of infection with powdery mildew was expressed as the number of spore s per cm(2). Statistical treatment of the data showed colour image ana lysis to be superior to the other two methods of evaluation. Major vei ns, light reflections and variations in the colour of leaves can degra de the accuracy of colour image analysis somewhat. These problems are, however, surmountable. Colour image analysis qualifies as a valuable new tool for accurate, objective, reproducible and detailed quantitati ve assessment of disease on leaves of plants.