GRASS GRUB: COPING WITHOUT CHEMICAL CONTROL

Abstract

A field experiment lasting four years in the Carew district of mid-Canterbury, investigated the recovery of ryegrass pasture severely damaged by grass grub. Overdrilling with grasses was unsuccessful, in this instance being done too late in spring. The time course of recovery of damaged pasture without and with insecticide was compared against resowing after a barley crop with either Ruanui or Nui ryegrasses, Maru phalaris or Matua prairie grass. Recovery of ground cover from damaged pasture was through infill by weed grasses and white clover. Insecticide maintained more ryegrass herbage. Yields from renovated pasture in autumn were considerably lower than those from renewed pasture. However, the renewed pasture was again generally severely damaged by grass grub within two years. The exception was Maru phalaris which was tolerant of grass grub. Yield of herbage from Maru in autumn was however lower than from more severelydamaged Matua pasture. Successful experience elsewhere with overdrilling Nui ryegrass into grass grubdamaged pasture is mentioned when such pasture was heavily stocked under wet soil conditions in early winter, then overdrilled in late winter. Keywords: Grassgrub, pasture renovation, renewal, overdrilling, tolerant grasses, biological control