Computer-assisted estimation of leaf damage caused by spider mites

The article describes a new method to assess the impact of the two-spotted spider mite, Tetranychus urticae Koch, on host plants. The method is based on measurement of the leaf area damaged using a computerized image analysis technique. Injured leaves were scanned on a common flat bed color scanner to obtain grey scale images. MATHEMATICA software was used for image analyzes. Leaf damage was defined as the ratio of the number of leaf image pixels in the damaged area to the total number of pixels of the entire leaf image. The precision of the proposed method was compared with two other methods based on the leaf damage index and the chlorophyll fluorescence, respectively. Results show that both the newly proposed normalized proportion of leaf area damaged (NPLAD) method and the leaf damage index method are sensitive enough to show significant differences in leaf damage after exposure to different densities of spider mites. The chlorophyll fluorescence method, in contrast, did not give satisfactory results. Advantages of the computer-assisted estimation of damage caused by T. urticae feeding are discussed.