Transmission, Field Spread, Cultivar Response, and Impact on Yield in Highbush Blueberry Infected with Blueberry scorch virus.

Scorch disease caused by Blueberry scorch virus (BlSV) spreads rapidly and radially from foci of infection. Healthy potted blueberry plants became infected when placed next to diseased field bushes from early May through mid-August. The aphid Fimbriaphis fimbriata, collected from infected field bushes, transmitted BlSV to healthy blueberry plants in controlled tests and was regarded as the most important means by which bushes in commercial fields became infected. The rate of spread in the symp-tomless cv. Stanley appears to be the same as the rate of spread in the cv. Pemberton, which exhibits blight and dieback. Most field bushes showed symptoms during the year following inoculation, but a few did not show symptoms until the second or third year. Many (30 out of 59) cultivars and selections infected with BlSV exhibited severe blighting of flowers and young leaves and dieback of twigs. Three cultivars showed only chlorosis of leaf margins. The virus was also detected in numerous cultivars (26 out of 59) that exhibited no symptoms, and they were considered tolerant of BlSV. The virus had no effect on germination of pollen from several cultivars. BlSV reduced yield in 'Pemberton', with the loss being related to the number of years bushes displayed symptoms. Yield was reduced by more than 85% in the third year of symptom expression. The virus did not significantly reduce the yield of six tolerant cultivars that were infected with the virus but displayed no symptoms.