Aspects of long-term use of herbicides: measurement of residues of diuron and simazine in an orchard soil

Abstract

At Bathurst, New South Wales, an apple orchard was treated with diuron and simazine annually for six years. One year after the last application the distribution of herbicide residues in the soil was estimated using a biological method. For simazine the usefulness of the alkali flame detector in gas-liquid chromatographic analysis was also investigated ; convenience and sensitivity compared favourably with bioassay. Residues of diuron and simazine in the surface soil (0-5 cm) represented 36-46 and 2-3 per cent of the annual application respectively. Diuron occurred to a depth of 40 cm but simazine was confined to the surface 15 cm of soil. Diuron residues were greater than expected from reports in the literature and apple trees exposed to high levels were damaged severely ; however, at recommended levels symptoms were only mild. Simazine had no deleterious effect on the trees even after application for six years at three times recommended levels.