Aerial applications of asulam: A bioassay technique for assessing buffer zones to protect sensitive sites in upland Britain

Abstract

Aerial spraying with asulam is commonly used to control bracken in upland Britain, and there is a possibility that drift from these applications may reach sites containing other sensitive species. Here a field-based bioassay experiment is reported where a sensitive species ( Rumex acetosa) was exposed downwind of an area being sprayed commercially with asulam (4·4 kg A.i. ha −1 in 44 litres spray ha −1) by helicopter in the North Peak Environmentally Sensitive Area in Derbyshire. Although drift of large droplets decreased rapidly, with most deposition within 35 m downwind, damage to the test plants was detected at distances of greater than 100 m. We predicted that the no-effect distance was 161 m and that a minimum buffer zone of > 160 m was, therefore, required to protect sensitive sites.