African feather grass was spotted in Ngapara, after also being reported earlier this year in m Waianakarua, the Otago Regional Council said last week.
The new incursion was discovered after a landowner recognised the pest plant on a factsheet at an ORC drop-in session.
ORC biosecurity staff visited the site and collected a sample, which confirmed it was African feather grass.
The tussock-like grass forms thick clumps up to 2m high and produces large amounts of seeds that are easily spread by wind or carried on clothing.
It could spread quickly, crowding out other plant species and potentially affecting the rural economy, the council said.
Surrounding properties in Ngapara are being checked.
An "incursion response plan" will be put together by the council to make sure the pest plant does not return or spread to other areas.
ORC portfolio lead Cr Andrew Noone said he wanted to thank the landowners for their "amazing response".
"And also thank our biosecurity, engagement and communications teams — it turns out the landowners saw a factsheet with African feather grass on it at the Oamaru session of our regional pest management plan review drop-ins and identified it there."
Anyone who thinks they have found African feather grass can report it online at orc.govt.nz/reportpests, noting the location and taking a photo if possible.
The ORC can also be contacted on 0800 474-082.
