Kiwifruit claim chairman John Cameron said it was "hugely significant" for the kiwifruit industry and other primary industries that the court also established that MPI owed a duty of care to kiwifruit growers when carrying out its biosecurity functions.
"We've waited a long time for this day and we are absolutely thrilled that the court has held that MPI owed a duty of care and breached that duty when it allowed PSA to enter New Zealand in 2009," he said in a statement.
"Biosecurity is critical to New Zealand, and our primary producers and economy are heavily reliant on MPI to protect our borders against known biosecurity risks such as Psa.
"MPI knew for many years that Psa was a significant risk to the kiwifruit industry, and if it had done its job properly and followed its own regulations and protocols under the Biosecurity Act, the PSA incursion would not have happened," Cameron said.
"Psa decimated the kiwifruit industry and its impact was far-reaching, not only on growers and their individual orchards, but on the New Zealand economy."
Judge Mallon said the Crown did not have any immunity from the claim under the Biosecurity Act, as it had claimed.
The court found that the then-MAF had responsibility for controlling what goods could be imported into New Zealand.
"MAF knew kiwifruit plant material was a risk good and that Psa was a disease associated with kiwifruit plant material," she said.
"It was, or should have been, obvious to MAF that if pollen was not free of plant material or other contaminants and was to be used commercially to artificially pollinate kiwifruit orchards, the vines and crops of those orchards were at risk of harm," Justice Mallon said.
MPI said it had not yet decided whether to appeal, adding that it was "carefully considering" the High Court's findings and its implications for current and future biosecurity measures.
The 500-page document traverses events dating back 12 years, pre-dating the establishment of MPI. "Once we have completed consideration of the judgment, a decision will be made on whether to appeal," it said.
The outbreak, which cost the industry an estimated $885 million, hit New Zealand's most productive growing areas on the North Island's east coast between 2010 and 2013.
LPF Litigation Funding, a New Zealand-owned company chaired by former Court of Appeal and Supreme Court Judge Bill Wilson QC, backed the claim.
The growers will be seeking about $500m in compensation from the Crown, an unspecified percentage of which will go to LPF.
The case, which took place in Wellington over 11 weeks last year, is one of New Zealand's largest ever class action suits. The trial was the first of two stages, with the original trial for the plaintiffs to prove the Crown breached its duty of care and establish a loss. The second stage will determine the level of costs incurred and compensation.
Psa swept through the kiwifruit heartland of the Bay of Plenty in 2010/11, hitting the gold variety known as Hort16a particularly hard.
The successful introduction of a new, Psa resistant cultivar, Gold3, has allowed the industry to bounce back strongly to well beyond pre-Psa production levels.
