Kiwifruit probe turns to length of Psa infection

A kiwifruit vine. File photo / Alan Gibson

The next stage in the containment of the Bay of Plenty kiwifruit disease outbreak will be establishing whether the bacteria has been in New Zealand for "10 years or 10 days", says an industry body head.

It was confirmed last night that the bacteria - Pseudomonas syringae pv actinidiae (Psa) - has infected New Zealand vines.

"If [Psa] has been here for 10 years and is quite widespread, but not having a big impact on vines and only presenting by leaf spot in a couple of orchards - that's a very different issue to if it's just been introduced and it's only present in a very small area," said Peter Ombler, president of New Zealand Kiwifruit Growers Incorporated (NZKGI).

Both situations had their advantages, he said.

Ombler said if the disease has been in New Zealand for many years, but was causing only minimal damage, that would mean it was something "we can live with".

That had been proven during a Psa outbreak in Japan, when that country was able to control the disease, he said.

Ombler said the other scenario - that the disease had recently arrived in this country - meant it could be contained and dealt with "quite quickly".

"We're just trying to come to grips with it," he said. "Containment is a smart option if we can get it quick enough."

Ombler said Kiwifruit growers were feeling "pretty anxious" about the outbreak.

"It's a very recent issue ... Our focus is now to communicate with growers to make sure they understand the risk and aren't inadvertently spreading this around the industry through bad practice [like] taking infected secateurs or tractors from one orchard to another."

Ombler said it was too early to say what the impact on New Zealand Kiwifruit growers would be if this country suffered a similar Psa outbreak to that seen in Italy, which had its industry was badly damaged by the bacteria.

"It's way too early to be saying that," he said. "The growing conditions here are completely different to Italy."

One option for containing the vine-killing bacteria may be to rip out the infected vines and burn them.

The strain of bacteria in New Zealand has not yet been identified, but the one which 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: $285.7 million.

Zespri is working closely with scientists and research partners to determine the most effective and appropriate control mechanism, which it says will partly be directed by the geographical location, proximity to other orchards and the site's risk profile.

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

But Zespri chief executive Lain Jager was more blunt when asked if the industry might seek to have the infected vines destroyed.

"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".

"I can't speak for MAF, but from an industry perspective, we would be working very closely with MAF to determine how that could be achieved".

Jager acknowledged a New Zealander with direct experience of the Italian disaster, Opotiki Packing and Coolstorage Ltd (Opac) managing director Craig Thompson, had said that the Italians had wrongly thought that normal measures such as removing and burning infected vines would get the outbreak under control.

"The severity of this outbreak is such that (that) hasn't been sufficient to control it," Thompson said in April after the disease gutted the company's million-tray 84ha Newgold orchard in Italy's Lazio region, and the company's directors warned that their $7 million investment should be written off.

Japanese efforts to use copper compounds and antibiotics against the disease led to the evolution of resistant bacteria, but Jager said experts said copper could be used in New Zealand to slow down the bacteria.

"Eventually this thing will settle down to where either we've eradicated it or there's a mature management regime, but in the meantime people will be thinking very hard about how to minimise their exposure," Jager said.

It was important to understand New Zealand conditions were not the same as in Italy, without a tremendously cold winter and there was no sign of cankers yet on the NZ vines.

"There are other strains of PSA in Japan and Korea and they manage it quite well," he said. "Where they have an infected vine, the orchardists cut it out and move on."

"We are at the beginning of an enormous learning curve".

Best-practice protocols yet to be developed for New Zealand might include copper foliar sprays, experimentation with antibiotics, and cutting and burning.

-WITH NZPA