‘Hellish’ spread of wild kiwifruit prompts ‘pest’ call from lobby group

Kiwifruit growers in New Zealand have long enjoyed some of the “best growing conditions in the world”, but those conditions look set to bite back.

Outbreaks of wild kiwifruit are threatening to run amok through the country’s native bush, carrying with them diseases and potentially harmful insects.

The “hellish” spread of the wild strain has prompted calls for it to be recognised as a pest, so that landowners, growers and regional councils can fight back.

Kiwifruit Vine Health analyst and compliance officer John Mather said his “pest” call was probably a first for an industry group – asking that the plant on which the industry was based be named a pest.

Mather took his case to a pest management meeting in Marlborough this week, saying wild kiwifruit in the top of the south could have far reaching implications, especially for Marlborough’s celebrated wine industry.

“Not only does wild kiwifruit impact indigenous biodiversity and production of forestry, it’s also a reservoir for disease organisms such as PSA and pests such as fruit flies and stink bugs,” Mather said.

“If these pests or disease got into Marlborough vineyards, it could have a detrimental effect on their growth.”

New Zealand Winegrowers biosecurity manager Ed Massey said the brown marmorated stink bug, a known kiwifruit hitchhiker, was a “high-risk” threat to the wine industry.

“Not only do they eat the grapes, but they taint the red wine,” Massey said.

“The defensive chemicals the bugs release when crushed affect the red wine juice and its quality.

“Should a population establish thanks to wild kiwifruit, Marlborough vineyards would have a lack of surveillance and control tools available to combat the threat they’d prevent.”

​Motueka’s Golden Bay Fruit owner Kerry Wilkins said vigilance in the orchard was key to preventing wild kiwifruit growth in the South Island.

“Kiwifruit that does fall to the ground gets blended up in the mower to prevent it from spreading elsewhere,” Wilkins said.

“Good hygiene in the orchard, like washing your hands, and being vigilant are two crucial aspects to preventing wild kiwifruit spread.

“While it’s a plant that sometimes grows in the area, it’s not a big problem right now.”

But on the other side of New Zealand, in the Bay of Plenty, wild kiwifruit was a much larger issue.

“In these areas, wild kiwifruit rapidly forms a heavy blanket of growth which kills, or topples, native trees and shrubs beneath,” Mather said.

Contractors had destroyed 14,600 wild kiwifruit vines in 2017.

New Zealand Kiwifruit Growers Inc. chief executive Nikki Johnson said kiwifruit grew well in New Zealand because it boasted some of the “best growing conditions in the world”.

“Clean air, fertile soils, a cool ocean, generous climate, and fewer pests and diseases all contribute to the unique quality and taste of New Zealand-grown kiwifruit,” Johnson said.

Mather said this meant the fruit would find it “easy to naturalise” in the South Island.

“There are around 900 to 1100 seeds per fruit and these have a high likelihood of germination,” he said.

Mather said wild kiwifruit outbreaks were “exacerbated” by unpicked fruit.

“Any fruiting vines that aren’t managed properly are targeted by birds who eat the wild kiwifruit and then spread the seeds into areas of native bush, forestry blocks and near orchards or farms,” he said.

Dumped kiwifruit were also said to be a major cause of wild kiwifruit flare-ups.

Mather said kiwifruit stickers near wild kiwifruit vines showed dumped kiwifruit were to blame.

“What’s interesting is that because kiwifruit stickers are changed each year, we’re able to find out in which year the scraps were originally dumped.”

Wilkins said South Island kiwifruit farmers were concerned about a wild kiwifruit outbreak because the fruit often harboured vine-killing disease PSA.

“At the moment, our district is PSA free,” Wilkins said. “We spray farmed kiwifruit for disease control purposes, but wild kiwifruit doesn’t receive this treatment.

“Everyone is concerned about wild kiwifruit because the PSA it could harbour would be quite detrimental to the industry.”

How to prevent wild kiwifruit:

Growers – Remove unpicked fruit from vines and mulch as soon as possible. This prevents mass feeding by birds and allows the fruit to compost as quickly as possible.

Post-harvest operators – Cover bins of rejected fruit to prevent birds feeding on ripening fruit.

Farmers – Cover stockpiles of fruit with shade cloth, windbreak netting or something similar, to prevent birds from getting to any fruit. Feed out only what will be eaten by stock at one time to prevent birds from eating leftovers.

The public – Be careful with the disposal of kiwifruit, particularly while out in the bush.

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