Susceptibility of southern highbush blueberry cultivars to phytophthora root rot

Phytophthora root rot is a serious disease of highbush blueberry (Vaccinium corymbosum L.) which is more susceptible than rabbiteye blueberry (V. ashei Reade). As acreage of southern highbush cultivars (hybrids between highbush and blueberry species native to the southeastern United States) increases so does the potential importance of this disease in southern blueberry fields. This study was initiated to compare the susceptibility of seven southern highbush cultivars and two rabbiteye cultivars to P. cinnamomi and to evaluate the effect of bed height and fungicide treatments on disease severity. After two years growth in Phytophthora infested sandy-loam soil, root rot symptoms were evident on plants throughout the field, but there were no differences in disease severity or plant vigor due to bed height or fungicide treatment. There were differences among cultivars. The rabbiteye cultivars, Tifblue and Premier, were more vigorous than the southern highbush cultivars, Marimba, Pearl River, Misty, Magnolia and Cooper. After five years, 100% of Premier, 90% of Gulfcoast and 76% of Tifblue plants were still alive and vigorous compared to less than 25% of Cooper, Magnolia, Marimba, Misty, Pearly River and Reveille. After five years growth in Phytophthora infested soil, 21% of plants drenched with metalaxyl twice a year for three years and 16% of plants grown on raised beds were very vigorous compared to 14% of plants grown in untreated soil and 9% of plants grown on flat beds. These results indicate that at least one southern highbush cultivar, Gulfcoast, has field resistance to Phytophthora root rot equivalent to the rabbiteye blueberry cultivars, Tifblue and Premier.