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In November 2010, kiwifruit growers discovered a highly contagious vine-killing canker that affects the vine of the kiwifruit but not the actual fruit. A number of kiwifruit orchards in Te Puke area were quarantined.

Situations like this are a major concern to the Ministry of Agriculture and Forestry (MAF), the ministry responsible for New Zealand’s biosecurity.

ZESPRI, New Zealand’s biggest exporter of kiwifruit, hopes New Zealand will be the first country to completely eradicate the airborne bacteria. MAF and researchers from Plant & Food Research are working closely with the orchards infected with the disease to reduce the risk of spreading the disease to other orchards. Orchardists have begun spraying the vines with copper and cutting them back.

Before November 2010, many of us had never heard of Psa and its threat to New Zealand’s biosecurity.

What is Psa?

Pseudomonas syringae pv actinidiae (known as Psa or batteriosi) is a bacterial disease that affects kiwifruit (Actinidia) vines. Psa poses no risks to human or animal health and does not affect plants other than kiwifruit vines. The disease impacts the health and viability of the plant, not the fruit directly. It is spread by airborne spores, meaning it is easily spread by heavy rain, strong winds, animals and humans.

What effect does it have on kiwifruit plants?

Early symptoms of the disease are brown, angular leaf spots, sometimes surrounded by a yellow halo, and leaf curl. In some cases in Italy, the bacteria has entered the cane of the vine causing visible cankers and can result in vine dieback or death of the plant.

What effects has it had on kiwifruit markets?

The disease was first seen on green kiwifruit vines in Japan about 25 years ago and on green kiwifruit vines in Italy in 1992. In recent years, outbreaks of Psa have devastated the industry in the northern Italian region of Lazio, including wiping out a New Zealand-owned gold kiwifruit orchard in the region. The disease is estimated to have cost Italy around 2 million euros. The disease has had different impacts in different environments – Psa is present in Japan and Korea, but the disease is controlled. New Zealand Plant & Food Research says the impact Psa has depends on the environment and also how it is managed.

What does it mean for New Zealand?

The discovery of Psa at a Te Puke orchard is the first time the disease has been found in New Zealand. The strain of the case found is yet to be determined, as is how it got into the country or what sort of effect it will have on the plants here. Kiwifruit exports are worth more than $1.5 billion to the New Zealand economy. New Zealand’s vines are coming into flower now and have yet to set fruit, which will not begin to be harvested until autumn 2011.

    Published 15 November 2010