REVIEW OF FACTORS ASSOCIATED WITH OFF-SITE ENVIRONMENT CONTAMINATION WITH THE INSECTICIDE IMIDACLOPRID FROM AUSTRALIAN SUGARCANE FIELDS

DETECTION OF THE insecticide imidacloprid in sugarcane-catchment waterways increased from 2008–2014, whereas application of imidacloprid by methods conforming to registered practice supposedly produces ‘residues less than the limit of quantification (0.05 mg/kg)’ in run-off, under irrigated conditions. From available information, and my observations and discussions with cane-growers and advisers, I suggest three groups of variables possibly influencing risk of imidacloprid flowing off-site. However, unknown pathways may also contribute. Firstly, insufficient filling and/or closure of coulter-slots into which liquid imidacloprid is applied facilitates escape of the insecticide into runoff; this situation being exacerbated by site variables e.g. soil type and slope. Deviations from the registered pattern of use (e.g. side-dress applications) may disproportionately exacerbate loss. Secondly, data interpolation suggests the liquid formulation has higher potential for off-site movement than the granular controlled-release (CR) formulation; with independent observation to support this. Thirdly, the simplicity to routinely treat for canegrub control rather than to use Integrated Pest Management Process to decide if, where, and with what formulation to treat, results in more-than-necessary treatment; especially if the liquid option is applied more than once in a 4–5 year crop-cycle. Despite the liquid formulations inherently greater environmental hazard, its contribution to risk can probably be mitigated by managing the other two sets of variables. Amenity for efficient canegrub control is justification for having both formulation types, each with respective advantages. Research, policy, and adoption recommendations are suggested to overcome this environmental risk and preserve continuing registration of both formulations.