Importes fodder beet seed contaminated with the seeds of the invasive crop weed velvetleaf entered New Zealand earlier than first thought, the Ministry for Primary Industries (MPI) has confirmed.
After velvetleaf plants began appearing in several parts of the country in February, MPI organised an intensive eight-week "search and destroy'' exercise.
Plants were recovered from 251 properties, including 55 in Southland and 45 in Otago.
MPI national incident controller David Yard said yesterday in a "very low number of properties'' the pattern of velvetleaf detection indicated second-generation growth.
"If the velvetleaf seeds had been planted with fodder beet seeds using a seed drill, we would have expected the velvetleaf plants to come up in straight lines, and we did see that.
"But on a few properties we found clusters of plants, which strongly suggests they were from plants which seeded the previous growing season.''
Mr Yard said that was not unexpected, as MPI inquiries found one line of fodder beet seeds which may have been contaminated had entered the country ahead of the 2015 growing season.
MPI did not know there was a problem with the seed until reports began emerging this year, he said.
Environment Southland (ES) led the search in Southland over almost eight weeks.
Hundreds of people were involved from organisations including local councils, agricultural and forestry companies, Fonterra, and some Southern Institute of Technology students.
ES biosecurity manager Richard Bowman said while velvetleaf may have seeded in Canterbury and possibly Otago last year, searching indicated it had not established in Southland.
"Here the most plants we found in one crop was 16 over several hectares ... so we really felt it was worth going the extra mile to stop the plants germinating.''
Mr Yard said MPI would meet all search costs.
That totalled more than $1million nationally, although regional breakdowns were not yet available.
Mr Bowman said it was "good to have clarity'' MPI would meet all costs, as a funding cap had been put in place after five weeks.
ES had already assembled all its invoices and sent them to MPI, Mr Bowman said.
He declined to give the total.
While the "search and destroy'' phase was over, there was still much work to do to ensure velvetleaf did not spread in future years, Mr Yard said.
A national co-ordinator was being appointed to look after velvetleaf management long-term, and a series of workshops would be held throughout the country next month.
As well as providing general information, there would be an opportunity at the workshops for farmers who had had velvetleaf discovered on their properties to meet "one on one'' with advisers to discuss future farm management, he said.
Mr Yard said farmers would need to be vigilant in future years.
Agricultural contractors also needed to improve machinery hygiene practices, after evidence velvetleaf seeds had been spread from farm to farm via dirty seed drills.
"Some seed spreading was promulgated by lax practices ... farmers need to be sure contractors use best-practice procedures.''
The fodder beet seed came from Italy and was certified by Danish authorities as meeting New Zealand's biosecurity regulations.
MPI plant germplasm imports manager Kathryn Hurr said the velvetleaf seeds were missed because the seeds were pelleted - coated with a material to make them round and uniform and easier to use in a mechanical seeder.
Interim measures were in place requiring seed merchants to send pelleted seed samples to a laboratory to be washed and tested, to ensure no rogue seeds were in the mix.
MPI officials would visit Europe soon to view the fodder beet seed supply chain, after which there would be consultation on possible changes to seed importing requirements.
Ms Hurr said that although New Zealand produced much of its own seed, it also relied on imported seed for crops such as lettuces, carrots and flowers and it was important seed was weed-free.
