Regular inspections and removal of nassella tussock to prevent its spread will be continued by the Otago Regional Council.
The pest plant threatens nearly 44,000ha in Otago.
Nassella invades and smothers other grassland species, grows just about anywhere and is unpalatable to stock.
It is also very similar to native tussocks which made its identification difficult and its seed could travel by air up to 15km, a report to the council's compliance committee said last week.
In Otago, it was found in the Cardrona Valley, Alexandra, Roxburgh and in the Waitaki near Oamaru.
"Nearly 44,000ha of Otago is designated as being at risk to this plant," council environment services manager Martin King said in the report.
About 7700ha was being inspected regularly by the council's regional services staff, who removed 3543 tussocks in the 2008-09 year.
"While no new sites have been found outside these locations in the last 20 years, new sites at these locations have been found."
Three field days had been held in Roxburgh to educate and assist the community to identify and control nassella, he said.
Monitoring showed a continuing trend of declining numbers of plants in Roxburgh, Alexandra and Waitaki.
"The sites in Cardrona are still producing some high tallies," Mr King said.
