Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/1998
Publication Date: N/A
Interpretive Summary: Botrytis blossom blight (Botrytis cinerea) sometimes causes extensive crop losses on rabbiteye blueberries (Vaccinium ashei Reade). The susceptibility of various rabbiteye and southern highbush blueberry (V. mostly corymbosum L.) cultivars and the susceptibility of their flowers at each developmental stage to Botrytis infection is unknown. Recommended fungicides are not always successful in controlling blossom blight in southern blueberry fields. This research documents the susceptibility of flowers at each developmental stage of 4 southern blueberry cultivars (Tifblue, Climax, Premier, and Gulfcoast). Flowers increased in susceptibility as flower stage increased. Flowers with the corolla exposed were most susceptible. In general southern highbush cultivars were no more or less susceptible to blossom blight than rabbiteye cultivars. Several systemic fungicides (benomyl, orbit, propiconazole, and cyprodinil) reduced ddisease severity when applied after infection; however, these fungicides were not effective when applied before infection. Captan was more effective when applied before infection. Gibberellic acid, a growth regulator sometimes applied during bloom to enhance berry set, decreased blossom blight severity. A surfactant tested with gibberellic acid and with two of the fungicides did not effect blossom blight severity. These results are important to the blueberry industry in the southeastern U. S. where the information will be used by extension pathologists making fungicide recommendations for control of Botrytis blossom blight, by plant breeders developing new disease resistant blueberry cultivars, and growers making decisions about which fungicides to apply for Botrytis infection during bloom and when these applications should be made.
Technical Abstract: Botrytis cinerea can cause a severe blossom and twig blight resulting in severe crop loss of rabbiteye blueberries. During bloom, 2-yr-old potted plants of the rabbiteye blueberry cultivars, Climax, Premier and Tifblue, and the southern highbush cultivars, Gulfcoast and Cooper, were inoculated with a conidial suspension of B. cinerea, and incubated for 2 days at 20 C and 100 RH. Flower stage was rated at the beginning of each study on a scale of 1 = dormant bud to 7 = corolla dropped. The efficacy of 5 fungicides for control of Botrytis blossom blight was evaluated by inoculating Climax and Gulfcoast plants either 2 days before or 2 days after treatment with each fungicide. Tifblue and Cooper plants were treated with the fungicide, propiconazole, 1 hr following gibberellic acid and surfactant applications, and inoculated the next day. Botrytis disease symptoms were scored 2 and 4 wk after inoculation on a scale of 0 = no symptoms to 7 = lesion extends into stem. Flower susceptibility increased as flower stage at inoculation increased. Buds that were at stage 1 to 3 at inoculation developed little blossom blight; while flowers at stages 5 to 7 developed more severe symptoms. Tifblue flowers at stages 5 to 7 were very susceptible to blossom blight. Flowers treated with benomyl, propiconazole and cyprodinil 2 days after inoculation had lower Botrytis scores than flowers that were not treated with fungicides; however, on Climax blossom blight severity was no different or was higher (propiconazole) on plants treated with these fungicides 2 days before inoculation than on the untreated plants. Captan reduced disease severity on Gulfcoast plants. Plants treated with gibberellic acid one day before inoculation developed less severe blossom blight than untreated plants.