ENVIRONMENTAL FATE OF PESTICIDES USED IN AUSTRALIAN VITICULTURE - BEHAVIOR OF DITHIANON AND VINCLOZOLIN IN THE SOILS OF THE SOUTH AUSTRALIAN RIVERLAND

The red calcareous earth soils of the South Australian Riverland produ ce more than one-third of the grapes used in Australian winemaking. As part of on-going investigations into pesticide transport in Australia n vineyard soils, the movement of the fungicides dithianon and vincloz olin through such strongly alkaline soils was investigated. Small, und isturbed soil cores were extracted from the inter-row topsoil of a vin eyard adjacent to the River Murray, approximately 10 km S.W. of Overla nd Comer, South Australia. The vines were grown in a deep (1 - 4 m) re ddish brown, strongly alkaline, sandy loam with a low organic carbon c ontent (1 - 2 %). Surface fluxes of pesticide were applied at the maxi mum recommended application rates to the surface of the cores, which w ere then irrigated, and pesticide residues in the leachate determined by HPLC. No leaching of either dithianon or vinclozolin occurred. Dith ianon was immobilised in the top 2 cm of the soil. Dithianon concentra tions were low (0 - 37 % applied dose) suggesting that rapid degradati on of this compound occurs in these soils (63 - 100 % degradation in 1 0 days). Extremely low concentrations of vinclozolin were found throug hout the soil core profiles (0.05 - 1.4 % applied dose) suggesting tha t this fungicide was somewhat mobile, but also that it too was unstabl e in such alkaline soils (> 98 % degradation in 10 days). These result s suggest that the irrigated vineyard soils of this region are unlikel y to be prone to leaching of dithianon or vinclozolin, and therefore t hat groundwater supplies in this area are unlikely to be at any signif icant risk of contamination through viticultural use of these compound s. (C) 1997 Elsevier Science Ltd.