Anticipating the unexpected – managing pasture pest outbreaks after large-scale land conversion

Abstract

Pasture pests are often held in check by natural enemies but we have observed that severe pest attack over a wide area can occur after large scale land use change. Data were reviewed from current projects and databases for pest density and damage records covering the past 30 years. The focus was on areas where large scale land change has been implemented, including new irrigation schemes, pasture development from tussock or scrub, and land moulding for drainage via “flipping” or “hump and hollow”. In these situations, pest outbreaks reached unprecedented levels, e.g. 2200 grass grub larvae/m² in the Amuri irrigation scheme, 770 porina larvae/m² on the East Otago Plateau and 3500 manuka beetle larvae/ m² at Cape Foulwind on the West Coast. With major land use change, a new environment is created where pest species are provided abundant resources and the initial invaders multiply rapidly, free from the pressure of natural enemies. Monitoring systems, to provide early warning of pest attack, and remediation strategies can be used to overcome damage by these pests.