95%。An image segmentation algorithm for the sugarcane diseases was proposed according to the characteristics of the sugarcane seedling red rot disease and ring spot disease images. Firstly, non-green plants including diseased spots, soils etc. were extracted using the color features of 2G—R—B and 2R—G—B. Secondly, some connected regions of non-green plants including soils etc. were removed using the segmentation based on area threshold. Finally, the shape features for the remaining connected regions of non-green plants including diseased spots, soils etc. were calculated using chain code, and the diseased spots were extracted according to the width, rectangle degree and roundness of the connected regions. The experimental results showed that this algorithm could effectively extract red rot diseased spots and ring spot diseased spots, the accurate rate of image segmentation for ring spot diseases was 93%, the accurate rate of image segmentation for red rot diseases was 95%.  