Submitted to: Fruit Varieties Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 1998
Publication Date: N/A
Interpretive Summary: One of the causes of crop loss of rabbiteye blueberries (Vaccinium ashei Reade) in the Gulf south in recent years has been death or injury of flowers due to late spring freezes. Southern highbush blueberry cultivars offer some protection against late spring freeze injury because they flower later than most rabbiteye cultivars. The area planted with southern highbush cultivars in the deep south is increasing; however, little is known about their susceptibility to disease. A disease that can easily be mistaken for freeze injury, Botrytis blossom blight, sometimes causes severe crop loss of rabbiteye blueberries, but usually is unimportant on highbush blueberry. This study showed that southern highbush cultivars do not differ as a group from rabbiteye cultivars in their susceptibility to Botrytis blossom blight. Of the five cultivars in this study, the southern highbush cultivar, Jubilee, and the rabbiteye cultivar, Premier, had the lowest Botrytis severity scores. Tifblue, a rabbiteye cultivar, had higher blossom blight scores than the southern highbush cultivar, Magnolia, or the rabbiteye cultivar, Climax. Blossom blight susceptibility was wn to increase a bud development neared full bloom, and Premier, Tifblue and Magnolia flowers at full bloom were especially susceptible. These results are important to growers and extension agents making disease control decisions and to researchers testing chemical controls of this disease.
Technical Abstract: The susceptibility of blueberry flowers at various developmental stages was evaluated by inoculating potted blueberry bushes of the rabbiteye cultivars, Climax, Premier and Tifblue, and the souther highbush cultivars, Magnolia and Jubilee, during bloom with a conidial suspension of Botrytis cinerea. Inoculated plants were then incubated in a dew chamber for two days at 20 oC and 100% RH. Flower stage was rated at the beginning of each study and two weeks after inoculation. Botrytis disease symptoms were scored two weeks after inoculation on a visual scale of 0 to 7. 'Jubilee' and 'Premier' had the lowest disease severity scores when averaged over flower stages; while 'Tifblue' had higher disease scores than 'Magnolia' and 'Climax'. The three southern highbush cultivars did not differ as a group in their susceptibility to Botrytis blossom blight from the two rabbiteye cultivars. Susceptibility to Botrytis blossom blight was greatest at later flower stages. Buds inoculated at stage 1 through stage 3 (prebloom) developed fewer disease symptoms, while flowers inoculated at stages 5 to 7 (full bloom) developed more sever symptoms. 'Premier', 'Tifblue', and 'Magnolia' flowers at stage 6 were very susceptible. Since susceptibility of blueberry flowers is greatest at or near full bloom, fungicide applications for Botrytis blight control of southern blueberries should be made beginning at flower stage 4 and continue through stage 6.