A bioassay method for formulation testing and residue studies of sulfonylurea and sulfonanylide herbicides

A bioassay method using the radicles of pea (Pisum sativum L.) and lupin (Lupinus angustifolius L.) was developed for the assessment of trials on herbicides of common use in the sulfonylurea class (chlorsulfuron, triasulfuron and metsulfuron-methyl) and in the sulfonanylide class (flumetsulam and metosulam). Soils within a range of pH 5.8–8.4 with textures from sand to clay were used in these experiments. The sensitivities of the species were similar in chlorsulfuron and flumetsulam trials and their response range varied with soil type and herbicide, e.g. between 0.75 and 6.0 ng triasulfuron g^?1 in the Wimmera grey clay and between 0.125 and 8.0 ng chlorsulfuron g^?1 soil in the Mallee sand. The method was demonstrated in a wide range of uses, encompassing tests of the initial bioactivity of formulations of chlorsulfuron and flumetsulam, monitoring the field leaching and persistence of triasulfuron and measuring relative potencies between the classes, using metsulfuron-methyl and metosulam. The bioassay response provided a high level of reproducibility and precision, which was measurable by the logistic curve-fitting procedure. In each case, R² values were >0.90 and lack-of-fit tests were clearly non-significant at the 0.05 level. Chi-square tests were used to measure differences between ED₅₀'s. The method does not require the pre-germination and selection of seedlings, daily watering or root-washing and results are obtained 7 days from sowing, providing favourable use for routine analyses and large-scale trials.     

Bioefficacy and leaching of controlled-release formulations of triazine herbicides

Conventional formulations of atrazine and simazine were compared with controlled-release formulations of these two herbicides for bioefficacy, leaching and crop safety in laboratory and field experiments. Three light-textured soils with a pH range of 5.8–8.5 were used for this work. An oat bioassay (Avena sativa L.) was used to quantify soil concentrations of the herbicides. Comparison of the initial bioefficacy of controlled-release formulations of atrazine and simazine showed their respective relative potencies to conventional formulations to be 0.51–0.85. The results indicated that the controlled-release formulations maintained an entrapped reserve of active ingredient after delivery with a conventional boomsprayer. In laboratory trials, the controlled-release formulations showed a reduction in leaching compared with conventional formulations. A controlled-release formulation and a conventional formulation of atrazine were tested further in a field trial. A higher concentration of atrazine in topsoil from the controlled-release formulation was observed 11 weeks after application after 107 mm of rainfall. It was deduced that this was caused by reduced leaching of the controlled-release formulation, as observed in laboratory trials. EWRC scores for the control of a range of grass and broad-leaved weeds were identical for both formulations. This indicated that, while the controlled-release formulation could inhibit leaching of the active ingredient, it did not hinder the level of potency necessary for early weed control. EWRC crop safety ratings of chickpeas (Cicer arietinum L.) sown at application were higher for the controlled-release formulation 10 weeks after sowing, and subsequent harvest yields were 50% higher. It was inferred that this resulted from a favourable interaction between crop growth and the timing of the release of the active ingredient from the controlled-release formulation. Altogether, the controlled-release formulations displayed the necessary prerequisites for their further development for large-scale use under arable regimes.