The giant buttercup is far more widespread in Southland than earlier believed - and the regional council there says the dairy industry needs to step up to the plate and deal with the threat to their pasture.
Cows won't eat the pest plant, which has been estimated to reduce production by $1000 per hectare in areas like Taranaki and Nelson Bays, where it's also wide-spread.
Southland Regional Council recently conducted a survey of 900 kilometres of rural roadsides and found the invasive weed along 10% of them.
Biosecurity manager Richard Bowman is worried a lot of Southland farmers simply don't recognise the threat.
He said Taranaki farmers would recognise giant buttercup, but most people in Southland have not seen it before.
Mr Bowman said it can be distinguished from other buttercups by its deeply serrated leaves.
He said the council wants to alert farmers to this threat because the pest plant can generally be dealt with if it is not fully established, but if it has gone right through a farmer's property and is part of the pasture then it is very difficult to get rid of.