The Ministry for Primary Industries says a hefty fine handed out to a seed importer following a biosecurity breach is not the end of the matter.
PGG Wrightson has been fined $57,000 in Ashburton District Court for a 2013 biosecurity breach.
In July last year PGG Wrightson insecurely transported a delivery of contaminated seeds and during the trip black grass seeds spilled off its truck throughout Mid-Canterbury - prime cropping country.
Black grass is a highly invasive weed that can significantly reduce yields of crops like wheat.
MPI response manager David Yard said a surveillance programme looking for signs of black grass in mid-Canterbury has another two years to run.
"We're now approximately a year into the surveillance programme which will last approximately three years. So we've so far completed nine rounds of intensive surveillance of the grass verges and surrounding area and to date we've found no evidence of any establishment of black grass seed."
Mr Yard said PGG Wrightson had also contributed about $300,000 to the cost of the surveillance.