Effects of some agricultural tank-mix adjuvants on the deposition efficiency of aqueous sprays on foliage

The effects of 10 commercially available tank-mix adjuvants on the retentio n and coverage of aqueous sprays on foliage were examined quantitatively un der track sprayer conditions, following application at their maximum recomm ended rates. Substantial enhancement of fluorescein retention was observed only on water-repellent barley and peas, but the differences in performance between the additives were considerable. Addition of the water-soluble tal low amine and nonylphenol surfactants gave the largest increases in retenti on, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex-or pinolene-based products or amm onium sulphate. Retention enhancement was also achieved using the mineral o il, vegetable oil, methylated vegetable oil and phospholipid ECs and the or ganosilicone surfactant, but this was often much less than that obtained fo r the water-soluble surfactants; the best EC was the methylated vegetable o il which also had the highest emulsifier content. Although spray quality wa s altered significantly in the presence of many of the adjuvants, modificat ions to this parameter alone could not account for changes observed in depo sition efficiency, because retention enhancement was recorded in sprays wit h volume median diameters both smaller and larger than water. There was a b etter correlation between retention efficiency and the dynamic surface tens ion of the corresponding spray liquids, with the exception of the organosil icone, which, as expected from its high surface activity, gave essentially complete spray coverage on leaves. Nevertheless, good coverage could still be achieved by adding the two water-soluble surfactants, as well as the met hylated vegetable oil and phospholipid ECs. Coverage performance of the oth er adjuvants tested was poor in comparison, reflecting, in part, their infe rior retention enhancing properties. (C) 2000 Elsevier Science Ltd. All rig hts reserved.