A Marlborough weed controller has been finding an increasing amount of wild grape and wild olive plants in the region.
Marlborough Plant and Food senior scientist Dion Mundy. Photo: Supplied / Stuff
Weed Solutions owner, and former Marlborough District Council biosecurity officer, Ben Minehan said because both plants were cultivated "on such a big scale" they could become a big weed problem.
"I am now starting to see wild grapes and wild olives that are starting to spread into the environment, that are in our reserve-type areas," Minehan said.
"Which is concerning because this has happened before with kiwifruit, they're spreading into the adjacent areas."
Wild kiwifruit vine on the North Island. Photo: Supplied / Kiwifruit Vine Health
He said he had spotted grape crops in Starborough Creek in Seddon, the Wairau River bed, Blind River, and on the Whangamoa Hill.
"Probably the one that concerns me the most is they were growing in the Grovetown Lagoon, on Māori Island," he said.
Every weed had a "lag phase"; the length of time it took for them to establish, Minehan said.
"I would be saying that we need to recognise this as an issue. They need to be controlled."
Anyone who spotted a wild plant should kill it before it could produce fruit, he said.
"The birds are picking the fruit up and moving it around.
"I found some olives when there was a crew of us spraying gorse for the Department of Conservation, and I found three olives growing up on the White Bluffs (on Marlborough's east coast). There are no olives growing out there, it must be birds.
"Because they're bird-spread plants, they'll end up being spread very quickly, to new areas.
"It would be nice to start recognising this early. The easiest thing you can do is kill a vine early before it spreads."
A wild olive tree Ben Minehan found on the Boulder Bank, Marlborough. Photo: Supplied / Ben Minehan
Marlborough District Council biosecurity manager Jono Underwood said most plants could self-propagate either by seed or discarded vegetative material - however not all self-propagating plants demonstrated invasive characteristics and became a biosecurity concern.
"It is more about how quickly and successfully they self-propagate, establish themselves and then dominate an ecosystem or productive system," Underwood said.
He said wild kiwifruit had shown it could do that, hence the "recent attention".
He said it was likely there were other species still to "show themselves". This was highlighted in the Parliamentary Commissioner for the Environment 'Space Invaders' Report, published in November last year.
"This is something the council's biosecurity team, with the help of the community, is always keeping an eye out for ... the new or unusual," he said.
Underwood did not think wild grapes, or olives, had "takeover, invasive" characteristics, so were not a concern for council.
Marlborough Plant and Food senior scientist Dion Mundy did not think wild grapes in New Zealand would be likely to "persist".
"But you can get vines growing from seed, grapes will do that. They will take quite a while to grow to a point where they produce fruit," Mundy said.
"They will, of course, be genetic recombinations of the parents who might be totally different varieties. They could be red, they could be white, they could be anything in between."
With the large number of grapes in Marlborough already, he did not think "one or two more" wild plants would make too much difference on disease pressure.
However, in the United States there were wild vines that were a reservoir for pests and diseases, but New Zealand did not have these particular pests here, he said.
"So I wouldn't be concerned about the odd grape growing and not being sprayed," he said.
"The only disease it might be a problem with is some of the virus diseases. If it got infected by virus and there was a lone vine outside someone's property, and it travelled on to an adjacent property," he said.
"But then someone's sauvignon blanc that doesn't show symptoms could spread to say a neighbouring pinot noir as well."
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