Imidacloprid can reduce the impact of the whitegrub Antitrogus parvulus on Australian sugarcane

Management of Childers canegrubs, Antitrogus parvulus Britton, is heavily dependant on organophosphate insecticides. As part of a programme to develop and integrate a wider spectrum of controls, we tested the potential of imidacloprid to control existing infestations of third-instar larvae in sugarcane. Two SC and one WG formulation of imidacloprid (Confidor^®) were tested in 11 trials near Bundaberg or Childers in southern Queensland. These defined useful application rates for the formulations, compared the efficacy of formulations, tested surface and subsurface placement, tested different spacings of the coulters behind which the insecticide was applied, and compared the efficacy of early and late applications of the insecticide. Comparisons were made with cadusafos (Rugby^® 100 G). Kill of larvae was not as rapid or great as following treatment with cadusafos, but surviving larvae appeared not to be feeding as much. Both SC formulations at rates of at least 3.75 g active ingredient/100 m of row applied into the soil behind coulters placed either side of the stool gave similar gains in cane yield to applications of cadusafos. The WG formulation showed some responses, but was not tested extensively. Application to the soil surface was not as effective as injection into the soil behind coulters. Efficacy seemed to be largely unaffected by the spacing between the coulters. Early applications appear to be more effective than later applications, and lead to larger yield responses. Imidacloprid provides a way of treating infested ratoon crops, does not degrade in high-pH soils, and can be used in rotation with the organophosphate-based cadusafos and chlorpyrifos (suSCon^® Blue) to minimise the development of insecticide resistance.