A third Bay of Plenty kiwifruit orchard has been placed under "restricted place notice" after symptoms of a bacterial infection were found on its vines last night.

Yesterday a Te Puke orchard was confirmed to have around 70 vines infected with the bacterium Pseudomonas syringae pv actinidiae (Psa), while neighbouring orchard was placed under "restricted place notice".

The United States and Australia banned imports of cuttings and nursery plants from New Zealand following the discovery.

MAF's biosecurity deputy director general Dr Barry O'Neil this morning told Radio New Zealand a third orchard, about 10km from the other two, was placed on the quarantine list overnight after symptoms of Psa were found,

"At this stage I must emphasis there is only one orchard that we laboratory tested positive, the other two that we have under restricted place notice are being restricted on the basis of clinical signs that we are observing in the leaves and laboratory testing will be undertaken today."

The results of those tests should be expected later today, he said.

As many as 18 orchards could be affected by the disease, MAF has said.

"We are following up on any suspicious signs of the disease, both within the Bay of Plenty and also outside of the Bay of Plenty," Mr O'Neil said.

He expected other countries would follow Australia and the United States by banning imports of nursery plants and cuttings.

"I think this would be a normal reaction from most of our trading partners and it would be the reaction we ourselves would take," Mr O'Neil said.

Further tests are to be done to determine the strain of the disease, and MAF is still seeking to determine how widespread it is and how it got into the country.

MAF is asking the public to stay away from all kiwifruit orchards as it continues investigations into the possible outbreak.

Psa carries no risk for humans and affects only the health of vines, not the fruit, MAF says.

Growers' meetings

Carol Ward, director of corporate and grower services at kiwifruit exporter Zespri, said meetings were held in the Bay of Plenty yesterday involving growers, contractors, MAF Biosecurity and industry leaders.

Growers were told to implement strict hygiene practices - such as sterilising equipment that moved between orchards - and informed of the need to inspect their properties for symptoms of Psa, which include spotted leaves.

"We just don't have all the answers to how widespread [Psa] is and what the potential response mechanism is going to be. It's going to be a few more days until we get a better view of that," Ward said.

Psa has caused widespread damage to Italy's kiwifruit industry since it surfaced there in 1992.

The bacterial strain in New Zealand has not yet been identified, but the one that caused the worst damage in Italy particularly affected gold cultivars - including Zespri's lucrative Hort16A.

Gold kiwifruit are the most profitable cultivar in New Zealand, making up 77,000 tonnes or 21 per cent of Zespri's production last season, but about 34 per cent of the crop's earnings at $285.7 million.

A MAF spokeswoman said tests were continuing yesterday at the orchard with confirmed Psa but results were not expected for two to three weeks.

It remains unknown how the bacteria found their way into this country. Growers in other regions, such as the Far North, have been told to be vigilant.

Ward said 80 per cent of New Zealand's kiwifruit were grown in the Bay of Plenty, with the industry contributing 20 per cent of GDP.

Port of Tauranga chief executive Mark Cairns said the outbreak was a concern, with the business putting through 700,000 tonnes of kiwifruit a year. "It sounds very serious and we're offering Zespri our moral support."

New Zealand Kiwifruit Growers Inc president Peter Ombler said it was possible Psa had been present in New Zealand for up to 10 years. The next stage in addressing the outbreak would involve establishing whether it had been here for "10 years or 10 days".

If the disease had been here for a long time, but was causing only minimal damage, that would mean it could be dealt with, he said. That had been proven during Japan's Psa outbreak, about 25 years ago, when that country was able to control the bacteria.

The other scenario - that the disease had recently arrived - would mean it could probably be contained.

A Zespri spokeswoman said control strategies "may take into consideration the need to remove and destroy the infected vines".

But Lain Jager, Zespri's chief executive, was more blunt. "If it looks like this thing is containable, I imagine that MAF would take a leadership position," he said. "In this case, that would probably involve cutting and burning."

* Pseudomonas syringae pv actinidiae (PSA) was first described in Japan in the 1980s.
* A different form of the disease caused economic losses in Korean orchards.
* First noticed in northern Italy in 1992, it began causing big losses in the Lazio region in 2008.
* The Italian outbreak showed damage was more severe on gold kiwifruit such as Zespri's Hort16A.
* The most conspicuous symptom is the red-rusty exudation on trunks and twigs.
* Cool temperatures, persistent rains and high humidity encourage the disease.

- Additional reporting NZPA, NZHERALD STAFF