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

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