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

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Abstract
Summary: 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.