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

The effects of 10 commercially available tank-mix adjuvants on the retention and coverage of aqueous sprays on foliage were examined quantitatively under track sprayer conditions, following application at their maximum recommended 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 tallow amine and nonylphenol surfactants gave the largest increases in retention, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex-or pinolene-based products or ammonium sulphate. Retention enhancement was also achieved using the mineral oil, vegetable oil, methylated vegetable oil and phospholipid ECs and the organosilicone surfactant, but this was often much less than that obtained for the water-soluble surfactants; the best EC was the methylated vegetable oil which also had the highest emulsifier content. Although spray quality was altered significantly in the presence of many of the adjuvants, modifications to this parameter alone could not account for changes observed in deposition efficiency, because retention enhancement was recorded in sprays with volume median diameters both smaller and larger than water. There was a better correlation between retention efficiency and the dynamic surface tension of the corresponding spray liquids, with the exception of the organosilicone, 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 methylated vegetable oil and phospholipid ECs. Coverage performance of the other adjuvants tested was poor in comparison, reflecting, in part, their inferior retention enhancing properties.