A different variant of Psa has been detected on two kiwifruit orchards. Photo/Supplied.
A different variant of Psa has been detected on two kiwifruit orchards, but the industry's leading biosecurity organisation says it has been evolving since it was discovered more than a decade ago.
Growers spoken to by NZME say there is no doubt Psa is the biggest risk to the industry, and they just have to learn to live with it.
Psa was first found on a Te Puke orchard in 2010 in Hort 16A gold kiwifruit vines. Hundreds of hectares of vines were consequently slashed back to the trunks, and it decimated the industry. The majority of those vines were replaced with Zespri G3, which was more tolerant to Psa, and there was a remarkable multi-billion dollar comeback.
Psa was more prevalent this year due to wet weather.
Kiwi Vine Health chief executive Leanne Stewart said it routinely detects variant forms and ''this is not unusual''.
''Bacteria – such as Psa – replicate very quickly and evolve much quicker than other organisms.''
The locations of the two orchards had not been disclosed, but as a precautionary step the growers had been asked to manage movements of any risk items from these properties.
Stewart said recent analysis undertaken this year of samples taken over time (in 2018, 2020 and 2021) had indicated the presence of a variant on two properties.
Kiwifruit Vine Health and Zespri had commissioned research to understand what the new Psa variant meant for the kiwifruit industry, and would re-commence Psa surveillance in spring, providing more information when available.
''We are awaiting further analysis of samples to learn more about the significance of this detection and its virulence in comparison to the common form of Psa. While this analysis is under way and as a precautionary measure, we have the full cooperation of the properties in being aware of the need to manage any potential biosecurity risk by not moving plant material.''
She said while Kiwi Vine Health was taking ''this seriously... We are well prepared to address any potential risk that could come with a new or different variant''.
There were many forms of Psa around the world, and it was called a different variant as opposed to a new variant as it had evolved within New Zealand, as opposed to being a new variant from offshore, Stewart said.
''The industry invests in a surveillance and research programme so that we can understand the potential impacts of such variants and take proactive action to manage risk. There is no evidence to date of new forms that have a greater impact to our industry, however, this is something that we are on the lookout for.''
Over the past 12 years, a significant amount of resources and funding had gone into a research and development programme to better understand and manage the disease, she said.
"Psa is well managed by growers and orchardists, who are successfully and routinely undertaking biosecurity practices that manage the risk of potential increases in impacts from the disease, and limit spread."
Kiwifruit Vine Health said in its Grower News bulletin earlier this month that seasonal risk calculators show winter Psa infection risk was generally higher this year in comparison to previous seasons for many areas. This was due to ongoing wet periods.
In the Te Puke, Whakatane, and Te Teko areas, Psa weather risk through June was around 40 per cent higher than levels seen in the previous four years.
Pāpāmoa kiwifruit grower Rob Thode said he was concerned because, in his view, Psa was mutating.
''I think it is something to worry about as KVH mentioned it in their Growers News. A variety of Psa was found a few years ago that was more copper tolerant.
''And copper is one of the things growers have used to push back on Psa.''
However, Stewart said KVH and Zespri, along with science partners, had been focused on learning more about copper resistance over the years.
It has been found at levels of increased tolerance but not at levels resistant to in-field levels of copper.
''We know that copper spraying at recommended rates is still effective at killing Psa strains with resistance mechanisms; and timing of spray application and weather conditions can have a big impact on the efficacy of copper use.''
Te Puke kiwifruit grower John Cook said storm periods in November last year caused a lot of damage to some orchards in parts of the Bay of Plenty, which had a significant impact on this year's harvest.
''There has been some pretty sad stories about how those vines and flower buds coped.''
That affected pollination, and a lot of growers had to pull fruit off when they were small.
''Yields were down... predominantly due to Psa coming in when the female flowers weren't suited to pollination.''
Cook appreciated the work done by Kiwi Vine Health, and said it had good warning systems in place which growers needed to take note of.
He said Psa was controllable to a point, but ''once you've got open wounds in the vines, Psa can get in and you can't protect them.''
Welcome Bay kiwifruit grower Mike Smith said any variant was obviously concerning, but he was confident Kiwi Vine Health was ''all over it''.
However, Smith said monocultures were always a risk, and when Psa took hold in 2010 it spread very quickly.
"We have just got to live with it [Psa]... worrying will do you no favours.''
That was the view of Te Puke kiwifruit grower Don Heslop, who said Psa was here to stay.
''We have got to get on and deal with it, or else it can get you down.''
Psa had added a lot of costs to the industry because of the monitoring and hygiene practices required to keep it under control.
''Yes, there is probably a bit more Psa around, but it has been a very wet season. Psa loves the wet and it loves the cold.''
New Zealand Kiwifruit Growers Inc chief executive Colin Bond said KVH had informed them about the variant, and it was important that growers understood and appreciated the precautionary measures they have undertaken, and that the detection has come from routine surveillance.
''NZKGI is confident that KVH will continue to keep our growers updated as [...] further analysis is undertaken, and any required next steps.''
Zespri was approached for comment but referred NZME to Kiwi Vine Health.
A Ministry for Primary Industries spokesperson said Psa was managed by KVH. It only became involved if a pest or disease was a new exotic organism to New Zealand.
There is still only one strain of Psa in the country at the moment.
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