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 lu pin (Lupinus angustifolius L.,) was developed for the assessment of tr ials on herbicides of common use in the sulfonylurea class (chlorsulfu ron, triasulfuron and metsulfuron-methyl) and in the sulfonanylide cla ss (flumetsulam and metosulam). Soils within a range of pH 5.8-8.4 wit h textures from sand to clay were used in these experiments. The sensi tivities 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 cla y 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, encompassin g tests of the initial bioactivity of formulations of chlorsulfuron an d flumetsulam, monitoring the field leaching and persistence of triasu lfuron and measuring relative potencies between the classes, using met sulfuron-methyl and metosulam. The bioassay response provided a high l evel of reproducibility and precision, which was measurable by the log istic curve-fitting procedure. In each case, R(2) values were >0.90 an d lack-of-fit tests were clearly non-significant at the 0.05 level. Ch i-square tests were used to measure differences between ED(50)'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.