More virulent PSA strain a new worry for kiwifruit growers

PETER WATSON AND FAIRFAX
Last updated 09:57 25/01/2011

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Nelson kiwifruit orchards continue to be monitored for more cases of the canker disease PSA (Pseudomonas syringae pv actinidiae), but at this stage, they remain free of a newly identified virulent strain.

The new strain may lead to more Bay of Plenty orchards being destroyed to contain the outbreak, which has caused consternation in the $1 billion export industry.

Of 126 orchards, including six in Motueka and two in Golden Bay, around the country that have been confirmed as having PSA, 25 have been identified as having what is known as the "Italian isolate" or strain, which appears to be the more deadly of two strains pinpointed by biosecurity officials last month.

The Italian strain was concentrated in orchards east of Te Puke, said John Burke, general manager of Kiwifruit Vine Health (KVH), a joint industry-Government organisation formed last year to control PSA and find a long-term management strategy.

The other strain identified just before Christmas was an Asian one, Mr Burke said.

This strain has been found outside the Bay of Plenty, and in all eight Nelson cases, and its symptoms have so far been confined to leaf spotting.

Orchards with the Italian strain have been hit far harder, with the disease spreading quickly.

Half of Italy's kiwifruit orchards have been devastated by PSA outbreaks in the past two years, but it has been controlled and managed successfully in orchards in Asia for more than 20 years.

Mr Burke said 15 hectares of kiwifruit vines in Te Puke had been pulled out. One orchard had been destroyed and major parts of two others pulled out.

More Italian strain-affected orchards were expected to become casualties, he said.

The vine destruction was likely to reduce fruit production by only 1 to 2 per cent, he said, but the national crop this year might not drop at all, because the growing season had been so good.

With the kiwifruit harvest due to start in a few weeks, KVH was now working with orchardists whose properties had been confirmed with the Italian strain, he said. It would buy the crop on the vines from the orchardists, and provide finance to help reinstate vines. All the growers planned to stay in the industry.

The Government and the industry agreed last year to jointly fund a $40 million campaign to fight PSA. Eradication is not an option, as the disease is too widespread.

Mr Burke said KVH's focus now was trying to ring-fence and contain the Italian strain within Te Puke, using copper and biological sprays. Orchards with the Asian strain were not unduly concerning KVH at this time.

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Ministry of Agriculture and Forestry specialists were working "to get to the bottom of it", using material and data gathered during the first PSA outbreak in September, he said.

Wet and cold weather, which stresses vines, is the big enemy in KVH's battle against PSA spreading. Orchardists are nervously awaiting the arrival of autumn and winter, when more effects of the disease could become apparent.

Mainland Kiwi Growers Entity chairman Roy Fry said local growers were carefully monitoring their orchards for further signs of PSA, but no more tests had been done, because the focus was on identifying the boundaries and size of the Te Puke "hot spot" and stopping it from spreading.

Restrictions on the movement of pollen and grafting wood were likely to be introduced by winter to prevent PSA from spreading further, he said. "We're still on a learning curve."

- Nelson

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