Histological studies and isolation experiments suggest that, contrary to previous descriptions, buds do not become infected by Didymella applanata via adjacent infected petioles. Buds at infected nodes were smaller than those at uninfected ones, but most were viable and capable of growth in spring if the correlative inhibition of healthy distal shoots was removed by excising and 'forcing' single nodes.
Tolerance of spur blight indicated by growth of strong laterals at infected nodes was higher in cv. Glen Clova than in cv. Malling Jewel and the yield of such laterals was no less than that at uninfected nodes.
Lesions predominate in the relatively infertile part of canes below ca. 45 cm, which in Scottish plantations is not harvested. Simulation of spur blight by disbudding showed that canes compensate for the loss of laterals up to 67 cm from the base by producing more laterals at the top of canes and heavier berries.
These results show that under Scottish conditions spur blight would substantially reduce yields only where lesions affect a high proportion of nodes in the cropping region of canes of intolerant cultivars, a rare combination.