Farmers in mid-Canterbury are angry seeds of a weed they say is the cropping industry equivalent of foot and mouth disease, were transported through the area and fell off the back of a truck.
The Ministry for Primary Industries has confirmed black grass seed spilled on State Highway 77 between Ashburton and Methven on 3 July. Farmers are asked to keep their eyes peeled for signs of the pest plant.
Black grass is notorious in Europe where it's highly resistant to herbicide, spreads rapidly, and reduces the yields of wheat, rapeseed, forage legumes and barley.
Federated Farmers grain and seed chair Ian MacKenzie of Ashburton says farmers are furious that MPI allowed PGG Wrightson's shipment of imported fescue seeds from Denmark to be driven though their region, when they knew it was contaminated with black grass seed.
About 20kg - 30kg of fescue seed is believed to have spilled. It's estimated to have contained 2,100 black grass seeds which MPI describes as about an "egg cup full".
Mr MacKenzie says the truck drove through the heart of some of the best cropping land in New Zealand.
He says black grass is one of the worst industry weeds that they contend with in Europe but New Zealand is free of black grass, which is a prohibited imported species.
Although farmers were impressed that MPI picked up the contamination at the border, Mr MacKenzie says they were disappointed that MPI allowed the seed to be shifted and with PGG Wrightson that protocols were not followed.
Farmers are now concerned that it may now lead to something like seven years of surveillance to ensure that black grass does not become established.
Mr MacKenzie says Federated Farmers is working with PGG Wrightson and MPI to try to ensure that black grass does not become established.
Other farmers in the area say MPI should have insisted the seed shipment was immediately destroyed.
Ministry spokesperson David Yard says the seeds are a low biosecurity risk and not many are likely to germinate because they are immature and most landed on barren ground.
"We anticipate that actually three to four seeds may germinate and grow along the roadside this year and maybe one to two next year - so it's quite a low number".
But Federated Farmers David Clark says black grass is a high risk.
"It's somewhat irrelevant as to how many of those seeds germinate, if 2,000 germinate or there's two of them - that's two too many and and it may actually make the job harder to find a very low number of seeds."
PGG Wrightson says it is working with the ministry following the biosecurity breach and it believes there is a relatively low chance that black grass seed will become established.
Labour Party primary production spokesperson Damien O'Connor says the incident smacks of lax biosecurity.
"To allow it into the country is just absurd and clearly the protocols need to be seriously reviewed."