Kiwifruit outlook defies disease

By Owen Hembry

Photo / Mark McKeown
Photo / Mark McKeown

The billion-dollar kiwifruit industry continues to battle a potentially devastating bacterial outbreak but the coming harvest is looking good.

In November New Zealand was found to have Pseudomonas syringae pv actinidiae (Psa) - a bacterial disease first identified in Japan about 25 years ago which in recent years has hit the Lazio region of Italy.

In New Zealand two types of Psa have been found - an Asian-like isolate and an Italian/French-like isolate.

John Burke, general manager of lead response organisation Kiwifruit Vine Health (KVH), said the Asian type had been found around the country and seemed to have been here for some time.

"But we also identified an Italian-like, French-like isolate which is very similar to the bacterium that has caused real devastation on kiwifruit, particularly gold, in Italy," he said.

"That really frightened the industry."

The Italian-like Psa was confined to quite a unique zone on the eastern side of Te Puke and could have arrived here within the past three years.

"So our spotlight has swung on to this infection because it appears that the Asian [type], while potentially damaging, is nowhere near as frightening as this other Italian-like [type]."

KVH has been working for the past three weeks on a battle plan under which, if the outbreak was confined and the perimeter could be determined, the host material could be cleaned out.

"Our biggest issue has been actually establishing where the perimeter of the zone is," Burke said.

"While we've got a reasonable picture [it's] not clear enough at this stage to go in holus-bolus and actually do large-scale removal of infected vines.

"We could spend a whole lot of money doing that and find that actually the infection is beyond where we thought it was."

KVH would introduce border and movement controls, and spray strategies within a wider zone, but in the meantime was trying to find the perimeter of the infection.

"We want to make sure our containment strategy covers where we're damn sure the infection is plus a bigger area - so putting a big circle around where we think the infection is."

But even if the perimeter could be determined the infection would not be eradicated.

"The idea is really to contain [it and] buy time until we can find a solution to deal with the problem."

Solutions could include protective sprays, on-orchard management, finding resistant varieties and understanding the life cycle.

"Already we have something like over 50 research and development projects under way."

The Asian-type Psa showed leaf spotting and seemed not to be progressing but the Italian type, particularly in gold kiwifruit, in some cases was showing a rapid movement to secondary dieback of shoots and in extreme cases cankers and weeping from vines.

Latest testing results show Psa confirmed on 147 sites, with about 29ha removed, equivalent to about 0.2 per cent of the total industry area.

Burke said it had been a brilliant growing season and from a big picture perspective the Psa incursion was relatively minor and would not affect production for overseas markets this year.

But he added: "It's something that if we leave it unchecked it can do some serious damage."

Melanie Palmer, of kiwifruit exporter Zespri, said the 2011 season was shaping well and the harvest would start in about a month.

"Last season we exported around 100 million trays and this season is looking fairly similar."

Zespri in its 2009/10 report said the volume of New Zealand-grown trays sold was 98.5 million.

Psa held no risks for human health and there was no evidence it could be transmitted on the fruit.

Psa outbreak

* 914 sites tested, 147 positive for Psa.

* 74pc of affected orchards in a 23km area south of Te Puke.

* 29ha removed, about 0.2pc of total industry area.

* Exporter Zespri says this season's harvest is shaping up well.

- NZ Herald

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