An investigation into a biosecurity alert over a consignment of Bulgarian maize found it posed no threat, the Ministry for Primary Industries says.
New Zealand First MP Richard Prosser has been asking why the ministry allowed maize - which it said was riddled with a noxious weed - into the country.
Mr Prosser said 37,000 tonnes of cheap Bulgarian maize were infested with noogoora bur.
He said it was an offence under the Biosecurity Act to allow noogoora bur to be sold, released or distributed in certain parts of the country.
He said the weed had the potential to devastate grain growing in Canterbury and the ministry had been slack.
However, Associate Minister for Primary Industries Jo Goodhew told Parliament the maize was treated and the noogoora bur seeds would not have been viable.
The ministry said it cleared the maize as being any kind of threat and, moreover, that it was hammer-milled, which would have killed any weed seeds.
Noogoora bur is poisonous to livestock and poultry, and can cause dermatitis in people and animals.