A technique for scoring midge blight of red raspberry, a disease complex caused by Resseliella theobaldi and associated fungi

A scoring technique is described for assessing midge blight using maps representing vascular lesions beneath periderm damaged by second generation larvae of Resseliella theobaldi . Individual canes were scored and some 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 most extensive in stout canes.