Bentazone - surfactant interactions in three selected weed species of differing leaf characteristics

摘要

The plant cuticle is a complex membrane, which covers the outer surface of the aerial portion of plants. It may act as a potential barrier to the penetration of foliage-applied herbicides. The beneficial effect of surfactants as adjuvants to facilitate spray droplet retention and cuticle penetration is well established, though the criteria influencing choice of surfactant is less so. This paper will report a study involving a series of fifteen non-ionic surfactants on the activity, uptake and translocation of a polar herbicide (bentazone; Log K_(ow), 0.45) when applied to three annual weed species of differing leaf surface characteristics. The surfactants belonged to the Plurafac~(R), Pluronic~(R) and Lutensol~(R) series (registered trademarks of BASF). The influence of these surfactants on the activity of bentazone was assessed by visual symptoms, membrane leakage (conductivity) and tissue succulence (fresh-weight/dry-weight). These effects were related to the physicochemical properties of the surfactants. Effects on the uptake and translocation of ~(14)C (bentazone) were evaluated over the initial 24 h treatment period. The results showed that surface properties and uptake of ~(14)C (bentazone) were enhanced by surfactants of low to medium hydrophilic-lipophilic balance (HLB) characterised by radical groups, low cloud point, a mean ethylene oxide (EO) number of <10 and no propylene oxide (PO) groups. A series of statistical analyses including ANOVA, MANOVA, Student Newman-Keuls, Multiple Regression and Partial Least Squares were performed. It was concluded that these surfactants may act as co-solubilisers/co-penetrators as well as influencing surface properties, Surfactant effects on systemicity of ~(14)C (bentazone) were normally indirect, resulting from enhanced absorption. When expressed as percentage of the absorbed dose of ~(14)C (bentazone) however, translocation was enhanced by selecting surfactants of higher EO number, particularly by members of the Lutensol and Pluronic groups. The study exemplifies the factors that can influence the target site delivery of such polar herbicides and underlines the importance of the appropriate choice of surfactant.