New hope for kiwifruit against Psa

By Amy McGillivray of Bay of Plenty Times -
Aespri Symposium run by the New Zealand Plant Protection Society. Photo / Bay Of Plenty Times
Aespri Symposium run by the New Zealand Plant Protection Society. Photo / Bay Of Plenty Times

Scientists are hopeful they have found new ways of limiting the damage done by the kiwifruit vine disease Psa.

A glimmer of hope was presented to several hundred involved in the crisis at a Zespri Psa symposium yesterday.

The symposium "A snapshot of Psa" featured industry experts covering a range of topics relating to the disease.

Italian scientist Giorgio Balestra and Plant and Food Research scientist Phil Elmer both presented findings about new products being tested that were proving successful in preventing Psa infection and reducing the damage it causes.

The disease was first identified in a Te Puke orchard in 2010 and has now infected 2050 orchards throughout the country, 1710 of them in the Western Bay.

Keynote speaker Mr Balestra from the University of Tuscia in Viterbo, Italy, presented new findings from research which has been carried out in Italy over the past four years.

The disease sprang up in Italy in 2008 and research has been under way ever since. Field trials of the new bacterial control agent (AMY - CO - X) have proven successful in both preventing the disease taking hold and reducing the damage done, Mr Balestra said.

Initially the product was developed to protect the flower as the usual copper treatment damaged the buds, but the trial has since been expanded to treating the whole plant throughout the season.

"It was a good result. It reduced it," he said. "We remark that we are able to reduce the disease, not solve the problem. If you have the pathogen already you can't get a miracle."

The agent worked to prevent Psa by competing for the same food and taking up the same space on the plant, creating an "organic film" on the plant, he said. In the same way it was able to see some reduction in the damage, he said.

There had been limited testing of the product in New Zealand but Mr Balestra supported more independent testing.

Despite the findings he was careful to point out prevention would always be fundamental in dealing with Psa.

"Normally the growers wait for the magic bullet."

Much of his work was to stress the importance of cleaning tools during pruning and deal properly with debris.

Mr Balestra said it was not enough to cut diseased vines off near the bottom as the reinfection rate was 80 per cent.

To get rid of the disease it was necessary to pull the vines out from the roots and re-plant the following season, he said.

Plant and Food Research scientist Mr Elmer also presented promising findings closer to home.

A three-component treatment being trialled in a Te Puke field has produced one of the first significant reductions in the severity of Psa in infected plants, he said. The treatment, made of TriMix 1, Actigard and Yeast Mix 2, has been so successful Zespri has asked for the commercialisation of the product to be fast-tracked if field trials remain positive.

Mr Elmer said the fast tracking means Zespri was looking to go to large-scale field trials this spring.

Trials are now under way to determine the role of each component in the mix.

It may be positive news for orchardists but Kiwifruit Vine Health chief executive Barry O'Neil stressed it was not a cure. "A single cure as far as a product for Psa does not exist and will probably not exist in the foreseeable future," he said.

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