Factors restricting control of greyback canegrub with controlled-release insecticide at Innisfail

The optimum position in the soil profile was determined for control of greyback canegrub with controlled-release (CR) insecticide suSCon®Blue, and studies were made on if and in what way control could be improved. Treatment with 21 kg/ha suS Con. Blue positioned 150-200 mm below the soil surface during planting or the first furrow cultivation reduced grub numbers and damage, and increased yield over plant plus first ratoon crops by 50-53 t cane/ha. Granules positioned 100-120 mm below the final soil surface during the fill-in cultivation were less effective. Positioning granules 150-200 mm deep is recommended on the registered product label and was already practised on these farms. However, root damage in the best treatments was more severe than previously experienced and chlorpyrifos concentration in soil was less than expected, suggesting that soil factors which degrade chlorpyrifos may be lessening local effectiveness of greyback grub control.