Abstract
Summary Goals: Previous sour rot research indicates the highest efficacy for sour rot treatments beginning prior to the onset of symptoms, yet many grapegrowers delay applications until after symptoms develop and continue weekly until harvest, which can exceed four sprays. This number of broad-spectrum insecticide applications is costly both financially and environmentally, and risks developing resistant populations of Drosophila fruit flies. The objective of this study was to determine the efficacy of a reduced number of spray applications beginning after symptom development, comparing weekly sprays totaling four applications to a reduced number of two to three applications based on total soluble solids. Key Findings: In both years of the trial, when chemical sprays were applied post-sour rot symptom development, more sprays did not equal more control. Reducing the number of post-symptom applications is a substantial cost-saving measure and is beneficial for environmental sustainability. In 2018, there were no significant differences between sour rot severity in both vineyard sites used in the trial. Incidence was significantly lower for the industry standard of weekly applications initiated at 15 Brix until harvest only in one vineyard site compared to applications at 16 and 20 Brix and applications at 16, 19, and 22 Brix. In 2019, there were no significant differences observed in disease severity and incidence between two sprays and weekly applications beginning at 15 Brix in both vineyard sites. Impact and Significance: Many growers choose to initiate sour rot control applications only after symptoms develop. Weekly applications are financially and environmentally costly, and the efficacy of timing applications initiated post-symptom development has yet to be researched. In this study, we show that a reduced number of chemical applications to control sour rot post-symptom development offers the same control as weekly sprays, consistent across both years of the study. Relying on weekly applications initiated only after sour rot symptoms develop does not significantly decrease incidence and severity at harvest. If sour rot symptoms are present, more spray applications do not offer better control.
Highlights
Key Findings: In both years of the trial, when chemical sprays were applied post-sour rot symptom development, more sprays did not equal more control
Goals: Previous sour rot research indicates the highest efficacy for sour rot treatments beginning prior to the onset of symptoms, yet many grapegrowers delay applications until after symptoms develop and continue weekly until harvest, which can exceed four sprays
The objective of this study was to determine the efficacy of a reduced number of spray applications beginning after symptom development, comparing weekly sprays totaling four applications to a reduced number of two to three applications based on total soluble solids
Summary
Goals: Previous sour rot research indicates the highest efficacy for sour rot treatments beginning prior to the onset of symptoms, yet many grapegrowers delay applications until after symptoms develop and continue weekly until harvest, which can exceed four sprays This number of broad-spectrum insecticide applications is costly both financially and environmentally, and risks developing resistant populations of Drosophila fruit flies. An important observation by Bisiach et al (1986) was that insecticidal sprays effectively targeted Drosophila spp. and lowered sour rot infection compared to untreated vines.[1] they noted that disease was best controlled when wounds were reduced and fruit flies were repressed, with the most significant reduction of sour rot from the use of plastic nets or cheesecloth that prevented fruit fly infestation This was further demonstrated by Barata et al (2012), who showed sour rot did not spread in wounded clusters that were excluded from fruit fly access using nylon nets around individual clusters.[2]. Treatments were assessed visually by sour rot incidence (percent of diseased clusters per vine) and severity (percent of affected berries per cluster)
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