Farmers are being asked to keep their eyes peeled for Chilean needle grass which is flowering and seeding at the moment.
They are also being asked to increase their on-farm biosecurity amid fears it could potentially infest 15 million hectares of land in the country.
Canterbury Regional Council principal biosecurity advisor Laurence Smith says 14 farms in the region are now affected.
He says it's unpalatable for stock and competes with preferred pasture species.
Mr Smith says it also has a long seed with a very sharp needle-like point which can attach itself easily to stock, machinery and people.
"So it causes stock health issues and can get into eyes and mouths and penetrate through skin and into the meat of the animals."
Mr Smith says for most of the year it's quite a difficult plant to detect and it's only at this time of year when it flowers that it is more easily identifiable.
He says there are practical steps farmers with the grass can take to stop its spread.
Mr Smith says it could be that they clean their vehicles before they leave the property and that they don't drive vehicles through areas which are infested with Chilean needle grass.
He says they could also have a dedicated vehicle which stays on the property, and another vehicle which goes off property.
Mr Smith says those farmers which don't have Chilean needle grass already could have signs to ensure anyone coming onto their property is aware of the problem.