Mobility and persistence of three sulfonylurea herbicides in alkaline cropping soils of south-eastern Australia

Biologically active residues of the herbicides metsulfuron-methyl, chlorsul furon and triasulfuron were estimated with field pea bioassays in soil samp les to 80 cm depth from 4 field trials in southeastern Australia situated o n neutral to highly alkaline soil. Residues were both mobile and persistent at low levels. Leaching occurred beyond the lowest sampling depth during t he winter-spring growing season. Metsulfuron-methyl was the most mobile of the 3 herbicides. Plant-back experiments involving susceptible crop and pas ture species on 2 of the sites showed that the rates of decline of these re sidues in the sampling zone were slower than might be inferred from label p lant-back recommendations in 1 of 2 seasons.