Muscadine Grape Berry Rot Diseases in Mississippi: Disease Epidemiology and Crop Reduction. N. Kummuang, Former Graduate Student, USDA-ARS, Small Fruit Research Station, Poplarville, MS 39470. S. V. Diehl, Assistant Professor, and B. J. Smith, Research Plant Pathologist, USDA-ARS, Small Fruit Research Station, Poplarville, MS 39470, and C. H. Graves, Jr., Emeritus Plant Pathologist, Department of Entomology and Plant Pathology, Mississippi State University, Mississippi State 39762. Plant Dis 80:244. Accepted for publication 27 November 1995. This article is in the public domain and not copy-rightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/PD-80-0244.

Four berry rot diseases that can cause severe losses of muscadine grapes in Mississippi were monitored throughout the 1991 and 1992 growing seasons on four cultivars (Doreen, Sterling, Carlos, and Cowart) at three locations in south Mississippi. Bitter rot (Greeneria uvicola) caused significant drop of young, half-size, full-size, and mature berries and was responsible for most of the fruit drop during the two growing seasons. Cultivars Sterling and Cowart had significantly more berry drop associated with this disease than did Doreen. Black rot (Guignardia bidwellii f. muscadinii) did not cause significant berry drop. Macrophoma rot (Botryosphaeria dothidea), ripe rot (Colletotrichum sp), and russet (unknown etiology) were not generally associated with berry drop of the cultivars in this study. At harvest in 1991, black rot was most severe on Cowart; whereas bitter rot was more severe on Carlos and Sterling cultivars. Incidences of Macrophoma rot and ripe rot were very low both years at all locations. The incidence of berry diseases at harvest was lower in 1992 than in 1991, probably because of the higher amount of rainfall during the early summer of 1991 compared to 1992. Only conidia of G. uvicola were abundant in rainwater runoff from the vines. Spore traps showed that the highest conidial peak of G. uvicola at Beaumont coincided with the highest peak of bitter rot disease on berries (young stage berries). Only the bitter rot pathogen overwintered in abundance on pedicels, fruit spurs, and mummified berries.