Frequency of occurrence and ground cover of Cirsium arvense on pastoral farms in New Zealand: a farmer opinion survey

To determine the peak cover of Cirsium arvense (Californian thistle) on pastoral farms throughout New Zealand (NZ), a postal and telephone-based questionnaire survey of 600 pastoral farms using a stratified-random sampling procedure was conducted. Three key results emerged from the analysis of data received from 502 responding farms: (1) overall, 89% of NZ farms support C. arvense (79%, 87%, 85%, 97% and 94% for beef, dairy, deer, sheep and sheep/beef farms, respectively); (2) the weed is spread across the entire farm in 45% of cases (35%, 40%, 56%, 50% and 53% for beef, dairy, deer, sheep and sheep/beef farms, respectively); (3) the peak percentage grazed area covered by C. arvense is overall 6% (4%, 6%, 6%, 12% and 6% for beef, dairy, deer, sheep and sheep/beef farms, respectively). This analysis provides the first quantitative information on the occurrence and cover of C. arvense on pastoral farms throughout New Zealand.