Effect of sulphur foliar applications on the tomato-potato psyllid (Bactericera cockerelli) in a potato crop

A field trial was conducted in 2012-2013 at Pukekohe to determine the efficacy of wettable sulphur, applied as a foliar treatment within a reduced insecticide programme, to control tomato-potato psyllid (TPP). Three of the four treatments included wettable sulphur (Kumulus (R) DF; at 6 kg/ha), either alone or in combination with other insecticides. The remaining treatment was a standard 7 day insecticide spray programme. Spraying for all treatments began at 60% plant emergence on 29 November 2012, and continued until 14 March 2013. The study demonstrated that although sulphur applications may reduce TPP nymph numbers on potato foliage, especially when used in combination with insecticides, sulphur alone is not an adequate TPP management strategy. The field trial results for sulphur-only treatments support previous work suggesting that although sulphur may slow the build-up of TPP populations by deterring egg-laying, the lack of repellence or anti-feeding properties still results in the transmission of Candidatus Liberibacter solanacearum by TPP. Given the ZC results, it is difficult to draw conclusions from this trial about the efficacy of sulphur/insecticide combinations for TPP management.