Occurrence and Prevalence of Foliar Diseases on Blueberry in Georgia

Abstract

Qualitative and quantitative information about the occurrence and prevalence of fungal species causing foliar diseases on blueberry in the southeastern United States is limited. To close this knowledge gap, a field survey was conducted in 2002 and 2003 involving a total of 177 samples (cultivar-site-year combinations) from plantings of rabbiteye and southern highbush blueberry cultivars in Georgia. Among eight cultivars, Powderblue was the least affected cultivar whereas Star had high foliar disease levels in both years. Averaged by cultivar and year, there was a significant positive correlation between defoliation and disease severity. Septoria leaf spot and Gloeosporium leaf spot were the most prevalent and most severe foliar diseases, occurring on > 30% of samples in both years. Pestalotia leaf spot, Phyllosticta leaf spot, and leaf rust occurred at intermediate prevalence levels. Among these three diseases, leaf rust was most severe (especially in 2003) whereas Pestalotia leaf spot was associated with secondary infections and occurred mostly on southern highbush cultivars. Algal leaf spot and powdery mildew occurred infrequently and inconsistently. More than 70% of leaf samples, especially from the rabbiteye cultivars, showed symptoms of non-pathogenic leaf damage. The foliar disease complex on blueberry in Georgia is considerably more diverse than previously appreciated. Accepted for publication 31 January 2008. Published 21 April 2008.