Control of Sour Rot via 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, typically associated with an abundance of Drosophila fruit flies. Uncertainties regarding disease etiology and epidemiology have limited the development of reliable management practices. 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 pre-harvest 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 an insecticide (spinetoram or zeta-cypermethrin, depending on year), both alone and in combination. Weekly applications of an antimicrobial plus insecticide provided an average 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 the three years, and significantly reduced the number of drosophilids recovered from the berries within the treated panels, whereas the antimicrobials were ineffective unless also applied with insecticide. Additionally, we studied disease development in a commercial vineyard of cv. Vignoles in which vines are trained to either a high wire cordon (HW) or vertical shoot position (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 enclosed fruit within an umbrella-like canopy, whose density between the fruiting zone and vineyard floor was greater than for VSP vines.