Modelling the farm scale impacts of clover root weevil herbivory

Abstract

Clover root weevil (Sitona lepidus CRW) is a major New Zealand pasture pest This study used computer simulation and decision support modelling to simulate CRW herbivory estimate the longterm consequences on clover abundance pasture production and quality and financial implications to a typical sheep and beef farmer Three farm scenarios were explored the absence of CRW and the presence of CRW with and without additional nitrogen (N) For a hypothetical 325 ha Waikato sheep and beef farm CRW decreased mean clover abundance from 21 to 13 pasture production from 9200 to 7900 kg DM/ha/year pasture quality from 105 to 102 MJME/kg DM and N fixation from 60 to 42 kg N/ha/year This resulted in a 16 reduction in the annual gross margin However assuming current prices and costs and that an N response could be consistently achieved urea could be used to replace the reduction in N fixation without affecting profits