Effect of Serratia entomophila and diazinon applied with seed against grass grub populations on the North Island volcanic plateau

Abstract

The bacterial biocontrol agent, Serratia entomophila, and the insecticide diazinon, were applied as separate granular formulations with ryegrass seed and compared with a seed-only control treatment on three pastures of different ages and composition on the North Island volcanic plateau. In the first 2 years, diazinon and S. entomophila significantly reduced healthy grass grub populations compared with the control. However, by the third year populations in the diazinon treatments had recovered and were significantly higher than in S. entomophila or control plots. Grass grub populations were reduced by disease outbreaks after S. entomophila was applied, which infected >40% of grass grub larvae in the treated plots in year two. Bacterial extraction from soil a year after application confirmed establishment and persistence of S. entomophila in treated plots. Visual positive pasture growth responses were noted in both the S. entomophila- and diazinon-treated plots.