Better disease control by using adjuvants
Abstract
Adjuvants can alter the surface tension of spray droplets and improve the spread of agrochemical mixtures on difficult targets like grape bunches. This offers the potential to customise pesticides application for maximum efficacy and minimum environmental risk. A series of laboratory trials in New Zealand and vineyard trials in Australia between 2002 and 2005 explored economic and efficacy gains when conventional, high-volume sprays were replaced with low-volume sprays that included organosilicone adjuvants. None of the five classes of adjuvant tested altered the phytotoxicity of a range of fungicide tank mixes. Laboratory spread tests showed none of the fungicide formulations reduced the effectiveness of any of the adjuvants. A modified organosilicone blend adjuvant, at concentrations recommended for use in vineyards, provided droplet spread that was up to ten times that achieved using the industry standard adjuvant.
Effective control of the diseases Botrytis, downy mildew and powdery mildew was achieved with considerably lower spray volumes (applying only 25-50 % of the dilute volume) in most field trials but could not be clearly attributed to specific use patterns of the organosilicone type adjuvants. There were no adjuvant, or adjuvant/spray volume combinations that consistently outperformed the others. In some trials, low volume applications with the new classes of organosilicone adjuvants provided equivalent disease control and spray deposits to the high volume sprays with conventional adjuvants, offering potential to save on labour and machinery costs associated with spraying. However, in other trials spray deposits or disease control resulting from low volume sprays with no adjuvant were equivalent to or better than low volume sprays that included organosilicone adjuvants. In some canopies, spraying with organosilicone adjuvants in half the dilute spray volume lead to excess wetting of outer canopy and net reduction in deposits. Because of the risk of overwetting, organosilicone adjuvants are not recommended for high volume fungicide applications.
Spray deposition and disease severity in bunches was determined primarily by the efficiency of delivery of fungicide spray to the inner canopy, which is independent of adjuvant. The high degree of variability in spray deposition within grapevine canopies introduces a withintreatment variability that potentially masks any effect of adjuvants.
Summary
Evaluation of a range of new adjuvants and their effect on spray droplet shape and penetration of grape bunches.