In the closing days of the 11-week court case brought by kiwifruit growers against the Ministry for Primary Industries over the 2009 outbreak of Psa, the government's lawyers insist it doesn't have a duty of care for biosecurity while the grower's group argues leaky building case law shows it does.

The group of 212 growers led by Strathboss Kiwifruit and Seeka claim the Ministry of Agriculture and Forestry (MAF) - which became part of MPI when that ministry was formed in 2012 - was negligent under the Biosecurity Act.

Pseudomonas syringae pv actinidiae - better known as Psa - infected 80 per cent of kiwifruit orchards nationwide and is estimated to have cost the industry up to $930 million in lost exports. The hearing started in the High Court in Wellington on August 7.

Jack Hodder QC, the government's lawyer, has already presented the Crown's case, while grower group lawyer Davey Salmon's closing arguments are set to continue today.

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Summing up MPI's arguments on Thursday, Hodder said the lawyers had not been able to find other cases which involved breaches of duty of care in this context because it is not a classic negligence case, and biosecurity was a different matter. This is not the kind of area where the tort of negligence has gone before, he said.

"Trains don't collide, stones don't get found in bungholes, snails are not found in ginger beer bottles, [and if they do] something has gone wrong, you can make that assumption," Hodder said.

"Biosecurity is much harder. The whole reason we have various compensation and response provisions in the act is because biosecurity risks materialise without fault on anybody's part. You cannot infer from a biosecurity fault at the end that there must have been some kind of problem to which the tort of negligence has something to say."

The plaintiffs need to demonstrate there was a clear and substantial breach, and a lack of reasonable care taken, Hodder said.

He argued there was a risk that hindsight and "a handful of emails" used by the plaintiffs as evidence could distort what was really going on at the time, and most of the scientific knowledge about kiwifruit and Psa post-dates the events talked about in the trial.

Salmon said the government lawyers had used an "elegant mischaracterisation" in arguing that the government doesn't have a duty of care and that the claim would open a floodgate to other litigation.

The government's lawyers had relied on some UK cases and older New Zealand cases to support the notion that the courts shy away from attributing public body liability, Salmon said.

However, he said the duty of consent his side argued for is an "almost perfect analogue for the gatekeeper role a local authority has when granting a building consent. The proper analogy is with those sort of operational statutory decisions on matters where the body has complete control and a duty to safeguard the public against the risks."

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Case law from the leaky homes saga supports the growers' case, Salmon said, where the Supreme Court demonstrated it didn't believe in the floodgates argument.

"In the case of Carter Holt Harvey last year, the Supreme Court said we know you have contracted to protect yourselves, we know that a duty of care runs counter to that and undermines it, but nevertheless it's happening," Salmon said.

"In the Supreme Court's deliberations, we see a disregard for all of the arguments my learned friends have raised. You could call this a novel duty case, but it's not actually novel in any other sense than that the Biosecurity Act hasn't been considered before."

The plaintiffs argued that Kiwi Pollen was the source of the Psa outbreak, and while the government disputed this, none of its witnesses gave evidence that the epicentre was anywhere else, Salmon said.