Decision tools for managing insect pest outbreaks in pastures

Abstract

Outbreaks of insect pests can cause major losses in pasture productivity, but farmers are often poorly equipped to evaluate risk factors, predict pest impacts and determine appropriate control actions. Decision tools are described for pasture pest management using three case studies. For grass grub, "at risk" paddocks are identified based on factors such as time since sowing, soil type and larval damage the previous autumn/ winter. Targeted populations measurements can then be taken and a decision to control grass grub made using this objective measurement and/or an assessment of the pasture value, termed the insurance approach. For manuka beetle, pesticide application decisions are based on damage scores of individual paddocks and the correlation between these scores and larval densities. With porina, information on moth flight times, larval populations and pasture damage are used to make key control decisions. For all pests, decisions to control should be made in conjunction with other farm systems information, including the costs of lost forage production and long-term impacts on pasture persistence. Keywords: grass grub (Costelytra zealandica), porina (Wiseana spp.), manuka beetle (Pyronota spp.), farmer decision-making