Californian thistle is probably the most invasive broadleaf weed in New Zealand pastures with reports estimating $700 million in lost pastoral farm revenue each year.
This perennial thistle limits farm productivity by reducing both pasture production and pasture utilisation. Trials show that 30% ground cover with Californian thistle (13 stems/m2) can cut ewe liveweight gains by 29% over a 12-month period. Californian thistle also triggers scabby mouth disease.