Midge blight, the death of fruiting raspberry canes that follows midge injury in their first year, is a consequence of fungal infection of the stele beneath periderm damaged by larvae of Resseliella theobaldi (Barnes) [see next abstract]. The lesions causing the greatest loss in yield are those attributable to attacks by the second, rather than the first or third generation larvae. A scoring technique that was developed in Scotland for assessing midge blight using maps representing vascular lesions beneath periderm damaged by second generation larvae is described. Individual canes were scored and certain components of yield examined. Yield was not affected until lesions covered more than 20% of the stele surface at the base of canes. Midge blight scores increased with cane girth, probably because splitting of the cortex was more extensive in stout canes.