Botrytis Blossom Blight of Southern Blueberries: Cultivar Susceptibility and Effect of Chemical Treatments.

Abstract

The susceptibility of blueberry flowers at each developmental stage was evaluated by inoculating potted blueberry bushes of the rabbiteye cultivars Climax, Premier, and Tifblue, and the southern highbush cultivars Gulfcoast and Cooper, during bloom with a conidial suspension of Botrytis cinerea and incubating in a dew chamber for 2 days at 20°C and 100% relative humidity. Flower stage was rated at the beginning of each study and at 2 and 4 weeks after inoculation. The efficacy of five fungicides (benomyl, captan, cyprodinil, cyprodinil + CGA173506, and propiconazole) and a surfactant for control of Botrytis blossom blight was evaluated by inoculating Climax and Gulfcoast plants 2 days before or 2 days after treatment with each fungicide. The effect of chemicals used during bloom on the severity of Botrytis blossom blight was evaluated by treating Tifblue and Cooper plants with gibberellic acid, surfactant, and fungicide combinations 1 day prior to inoculation. Botrytis disease symptoms were scored 2 and 4 weeks after inoculation on a visual scale of 0 to 7. Flower susceptibility increased as flower stage at inoculation increased. Tifblue flowers at or near full bloom (stages 5 and 6) at the time of inoculation were very susceptible to Botrytis blossom blight. Flowers treated with benomyl, cyprodinil, and cyprodinil + CGA173506 2 days after inoculation had lower Botrytis severity scores than inoculated flowers not treated with fungicides. Flowers treated with gibberellic acid 1 day prior to inoculation had lower Botrytis scores 2 and 4 weeks later than untreated flowers, while flowers treated with a nonionic surfactant received the same Botrytis severity scores as untreated flowers.