Airborne pest could be hard to eradicate

Photo / Steven McNicholl

The kiwifruit industry's struggle with a vine-killing disease could just be beginning, as biosecurity officials conceded that the option of eradication was slipping away.

A week after the Pseudomonas syringae pv actinidiae (Psa) bacterium was first detected in a Te Puke orchard, 116 growers suspect their vines have been affected. Some of these were outside of the Bay of Plenty, where the first infections were recorded.

The Ministry of Forestry and Agriculture said yesterday only three orchards were confirmed to have the disease, and another three were quarantined. The six restricted sites were 10km apart in Te Puke and all produced gold kiwifruit.

However, the full spread of the bacterium was not yet known. The disease was capable of spreading "silently", or without showing symptoms.

Agriculture Minister David Carter said the airborne nature of the disease meant ridding orchards of infection was becoming more difficult.

"We are not in a position ... to make a categoric decision as to the opportunity to successfully eradicate this disease, although it is fair to say that it is looking increasingly difficult to eradicate Psa from New Zealand."

A decision is likely to be made this weekend as to whether eradication is possible. This would require burying or burning whole blocks of kiwifruit crops.

Mr Carter said several more days would be needed to make a decision on eradication or containment, as test results from 70 orchards were expected by tomorrow. Growers had agreed to wait for more samples before decisive action was taken.

Zespri chief executive Lain Jager said the industry's mind was now turning managing Psa on a long-term basis. Authorities reported that there was anecdotal evidence that the disease had been detected in vines in previous seasons.

Mr Carter said, "If we could confirm that, it does suggest ... that the kiwifruit industry has learnt to work with that, and achieve good results, managing [the disease] almost inadvertently."

Historical cultures were being investigated for signs of Psa.

Plant pathologist John Young said it was likely the pathogen had been in the country for some time, possibly years.

"These diseases routinely lie low, even for five years. Nothing shows, nothing shows, then you get a worrying disease."

The pathogen thrives in cold conditions, usually below 20C. In Italy, an devastating epidemic in kiwifruit orchards occurred after a bitterly cold winter. The pathogen normally infects a vine in autumn conditions, before emerging in spring.

After a tense week in which crops and jobs hung in the balance, much of the initial anxiety among growers has subsided. NZ Kiwifruit Growers President Peter Ombler said it had been a "rollercoaster" of a week but orchardists had responded pragmatically to the threat.

Orchardists in Coromandel and Franklin had also suspected symptoms of Psa, but these cases were not confirmed.