TECHNIQUES TO REDUCE THE IMPACT OF ASULAM DRIFT FROM HELICOPTER SPRAYERS ON NATIVE VEGETATION

Asulam is often applied from the air to control bracken. This herbicid e affects other ferns and spray drift could affect their survival. Thi s paper discusses the use of bioassays to assess drift (a) spatially a round a single bracken patch, (b) downwind from sprayed areas, and (c) spatially in undulating terrain and with different vegetation cover t ypes. The aims were to develop policies to protect sensitive habitats. It is suggested that ''no-spray'' buffer zones in excess of 160-180 m are needed to minimise risk. Protection of rare ferns from overstorey vegetation or from steep slopes did not occur. Although less drift wa s found upwind there was significant damage at the end of the helicopt er runs because of errors in switching the sprayer on and off. (C) 199 6 Academic Press Limited