Canterbury farmers are still being encouraged to report sightings of saffron thistle.
Environment Canterbury (ECan) has asked farmers to watch out for the thistle, also called Carthamus lanatus, and report anything they thought looked like it.
The issue was raised late last year, but rural residents were asked to remain on alert.
Saffron thistle is a declared pest in Canterbury's Regional Pest Management Plan.
ECan's principal resource management adviser for biosecurity, Laurence Smith, said although it was not a widespread plant, there were isolated sites of it throughout Canterbury.
''We encourage landowners to report sightings, as this plant has significant potential distribution across our region,'' he said.
ECan works with landowners to eliminate plants at all known sites annually.
''This is to prevent seeding in an effort to reduce population density [and] plant numbers,'' Mr Smith said.
''Over time, we hope to reduce the number of sites. However, it is difficult to know the extent of the plants' seed bank in the soil. By doing this work, while the number of sites are low, we are preventing what could be a costly future impact on our agricultural industry.''
He said landowners should be vigilant on their properties and practise farm biosecurity measures to reduce the risk of potentially contaminated goods, vehicles and machinery bringing new pests, such as saffron thistle, on to their land.
''We ask anyone who suspects they have saffron thistle to let us know as soon as possible. It will be flowering and easily identifiable with its yellow flowers from December to April.''
-By Alexia Johnston