Control of Sour Rot Using Chemical and Canopy Management Techniques

Abstract

Sour rot is a disease complex characterized by rotting of the grape berry plus internal development of acetic acid, and it is typically associated with an abundance of fruit flies (Drosophila). Uncertainty regarding disease etiology and epidemiology has limited the development of reliable management practices for sour rot, but it is now known that yeast, acetic acid bacteria (AAB), and Drosophila spp. act together to cause the disease. Thus, we conducted three years of replicated field trials on the Vitis interspecific hybrid cv. Vignoles, in which we targeted these organisms through preharvest applications of various antimicrobial agents (potassium metabisulfite, copper hydroxide, BLAD polypeptide, and/or a mixture of hydrogen dioxide and peroxyacetic acid, depending on year) and insecticides (spinetoram or zeta-cypermethrin, depending on year), alone and in combination. Weekly application of an antimicrobial plus insecticide provided an average of 64% control relative to untreated vines across all three years of the trial when initiated preventively at 15 Brix, before the onset of symptoms; withholding addition of an antimicrobial to the insecticide application until symptoms appeared typically decreased the control level. Applying only an insecticide on the preventive schedule provided substantial control in two of three years, and significantly reduced the number of drosophilids recovered from the berries within the treated panels, whereas the antimicrobials were only effective when applied with insecticide. We also studied disease development in a commercial vineyard of cv. Vignoles in which vines were trained to either a high wire cordon (HW) or vertical shoot positioned (VSP) system in groups of adjacent rows. In all three years of monitoring, disease severity was significantly higher on vines in the HW system, where drooping shoots formed a canopy over the fruit, and in which canopy density between the fruiting zone and vineyard floor was greater than for VSP vines.