Poster: Biology & Disease Mgmt: Chemical Control
Etiology and management of sour rot in grapes
M. HALL (1), M. Hall (1), G. Loeb (1), W. Wilcox (1) (1) Cornell University, U.S.A.
Sour rot is a major challenge for affected grape growers and winemakers worldwide, yet basic disease etiology and management techniques are not well understood. Symptoms are characterized by fruit rot accompanied by the smell of acetic acid and presence of Drosophila (fruit fly) species. We’ve successfully reproduced these visual and olfactory disease symptoms and the accompanying characteristic production of ethanol and its conversion to acetic acid within affected berries, in the lab. Healthy fruit were wounded, inoculated with Saccharomyces cerevisiae and Acetobacter aceti, and exposed to D. melanogaster adults. Inoculation without exposure to flies significantly promoted ethanol production but not acetic acid generation, whereas concomitant exposure to flies resulted in both. In field trials conducted on cv. 'Vignoles' in 2013-15, both insecticide and antimicrobial treatments significantly reduced sour rot development. In 2015, untreated vines averaged 20.5% sour rot severity, and this was reduced by 73-81% on vines treated prophylactically post-veraison with weekly sprays containing a combination of the insecticide zeta-cypermethrin plus the antimicrobial potassium metabisulfite or hydrogen dioxide; severity was reduced by 49% on vines receiving only insecticide sprays. These trials further support the hypothesis that sour rot results from a complex of yeast, bacteria, and Drosophila, and that targeting these organisms can provide significant levels of control.