Time of Infection and Control of Phomopsis Fruit Rot of Grape

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Abstract
Phomopsis viticola, the cause of Phomopsis cane and leaf spot, can incite a fruit rot of grapes in addition to necrotic lesions of the canes and leaves. Fruit rot had occurred in New York during years with unusually high rainfall (> 100 mm) during bloom. Inoculations of Vitis labrusca ''Concord'' clusters at or shortly after bloom using 1 .times. 107 alpha spores per milliliter resulted in 16-30% fruit rot at harvest. Inoculations at earlier or later growth stages did not result in fruit rot significantly higher than that in nontreated controls. Berries inoculated in the laboratory were progressively less susceptible to infection and colonization as they aged from pea-size to ripe stages of growth (Eichhorn and Lorenz growth stages 30 to 38). Wounding of the fruit was not a prerequisite for infection. Infection and symptom development occurred faster on berries incubated with the pedicel in contact with inoculum than on those with the stylar end in contact with inoculum. Latent infections of fruit and rachis were detected using a paraquat dip technique. Two applications of mancozeb during bloom significantly reduced fruit rot and rachis lesions on cv. Delaware during the 1987 growing season. We suggest that protectant fungicides applied during bloom (Eichhorn and Lorenz growth stage 25) will significantly improve control of fruit and rachis infections.