A mosaic disease that affects this cv. is probably caused by raspberry leaf spot virus alone, although diseased plants from the field also contained raspberry leaf mottle and black raspberry necrosis viruses. All these viruses spread slowly in plantations of Glen Cova (possibly because this cv. has some resistance to their aphid vector, Amphorophora rubi) but rapidly in plantations of Malling Jewel, in which the viruses induce no symptoms. Mosaic disease occurred predominantly around the edges of Glen Cova plantations, especially where these were next to crops of Malling Jewel. To limit the incidence of mosaic, growers should ideally plant Glen Cova in large square plots, avoiding proximity to Malling Jewel and other raspberry cvs. likely to act as sources of infection.