Response to clover root weevil outbreaks in South Canterbury, Otago and Southland: the agricultural sector and government working together

Background Clover root weevil (CRW) breached NZ biosecurity, was first detected in 1996 in Waikato and Auckland, and has since spread nationwide. Following a decade of research, the parasitic wasp Microctonus aethiopoides was introduced from Ireland for biocontrol in 2006. It was quick to suppress CRW in the North Island and northern South Island, but was slower in Otago and Southland where its natural dispersal rate is lower and conditions in 2013 and 2014 promoted high CRW populations; damage to white clover became severe and widespread. Approach A programme began in 2014 that aimed to distribute 1M wasps across Otago and Southland by winter 2015. It is funded by AgResearch, Dairy NZ and Beef+Lamb NZ, and receives in kind support from seed and fertiliser companies, farm consultants and farm discussion groups. Results To date, over 0.85M wasps have been distributed to 4000 sites across Otago and Southland, establishment has been confirmed at all 50 sites checked, and releases are ongoing. Parasitic wasps were collected from pastures where they were already abundant and either released directly on farms, or provided to farmers via 29 field days. Over 40 farmers collected an estimated 0.25M wasps themselves from AgResearch’s farm at Invermay. Conclusions Pasture damage was rapidly minimised by long term research, government’s strong commitment to farming, and effective collaboration between science and industry. Practical implications of conclusions The period that Otago and Southland pastures would have suffered severe damage from CRW was shortened by 7-9 years, saving over $3M per year.