Submitted to: National Berry Fruit Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 27, 1998
Publication Date: N/A
Interpretive Summary: Rabbiteye blueberry (Vaccinnium ashei Reade) production in the southeastern U. S. more than doubled between 1982 and 1992. The fungal disease, Botrytis blossom blight, caused severe crop loss of rabbiteye blueberries in early spring of some years with symptoms resembling freeze injury. Since fungicial control of Botrytis blossom blight often has been unsatisfactory, ,the objective of this study was to determine the efficacy of fungicides fo control of this disease on rabbiteye blueberry. Four fungicide treatments, benomyl plus captan, vinclozolin, fenbuconazole, and azoxystrobin, were shown to reduce the severity of blossom blight when applied to rabbiteye blueberry flowers at or near full bloom. Pre-infection applications of these treatments reduced disease levels more than post-infection applications. Two fungicides propiconazole or iprodione severely injured or killed flowers. This damage was most severe if the flowers were exposed dto high humidity immediately after the fungicides were applied. The results of this study are important to growers and extension agents making disease control decisions. Since the beneficial fungicides were most effective when applied before infection, growers will need to make applications when weather reports indicate that conditions conducive to Botrytis infection are likely to coincide with the more susceptible flower stages. the demonstration that two of the fungicides were phytotoxic to rabbiteye blueberry flowers should result in label use restrictions of these chemicals preventing their application to rabbiteye blueberries during full bloom.
Technical Abstract: Six fungicide treatments, benomyl + captan, iprodione, vinclozolin, azoxystrobin, fenbuconazole, and propiconazole, were evaluated for their efficacy for control of botrytis blossom blight by applying the treatment two days before or two days after inoculation with the pathogen, botrytis cinerea. Potted blue berry bushes of the rabbiteye cultivar, Climax, were inoculated during full bloom with a conidial suspension of B. cinerea, and incubated in a dew chamber for two days at 20 deg C and 100% RH. Flower stage was rated a 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. Flowers treated with benomyl + captan, azoxystrobin, fenbuconazole, and vinclozolin had disease severity scores as low as the uninoculated controls. Flowers treated with benomyl + captan two days prior to inoculation had significant lower disease severity scores than flowers treated with this combination two days after inoculation. Flowers at stages 5, 6, and 7 when treated with propiconazole or iprodione were severely injured or killed even when they were not inoculated.