Black-grass may not be as invasive and hard to control in New Zealand as in other countries, the Ministry for Primary Industries says.
Alopecurus myosuroides, known as black-grass or twitch grass. Photo: Wikicommons
The weed has proved damaging to wheat crops in the United Kingdom and Europe, where it has also become resistant to certain herbicides.
The ministry has been working with farmers to clear an outbreak in mid-Canterbury.
The ministry's response manager, David Yard, said it came from a consignment of ryegrass imported in 2007.
Seed from that consignment had been planted on 24 farms.
"We've actively surveyed all 24 of them, but black-grass was only found on three, which tends to suggest that whilst black-grass is very invasive in Europe, and can spread very quickly, given these plants may have been there since 2007, the levels of plants we found we actually found was quite low.
"That suggests, with the herbicides sprayed by farmers and the different climate of New Zealand, that black-grass may not be as big a problem as we feared in the past."
Mr Yard said the weed had been removed from the three properties and MPI would keep monitoring the area for it.
"What we're actually doing is working with the farms that are under surveillance, and in particular we have seven, who we believe are of higher concern.
"So we're introducing what we call a management plan, so each farmer will be visited, and they'll be given advice about what herbicides to use, what crops to grow and what to look for."
