Purple loosetrife, pinus mugo and Darwin's barberry Photo: Commons
Environment Southland has warned against backyard nurseries selling pest plants on social media.
In the past three years the council has discovered individuals selling cotoneaster, buddleia and an invasive succulent known as pig's ear.
A commercial nursery was also found selling a variety of a wilding pine.
The regional council is fighting back against invasive plants and is asking Southlanders to check their ponds for parrot's feather and their gardens for purple loosestrife with the hope of eradication.
Purple loosestrife, an attractive purple plant, is a big problem, Environment Southland biosecurity pest plants team leader Jolie Hazley told RNZ's Nine to Noon.
"It was legally allowed to be a sold in nurseries 20 years' ago, and then it was discovered that it's actually one of the worst weeds in the world."
It's now on an eradication list, she said.
"It's mainly in people's gardens, as it hasn't escaped yet into the wild too much in Southland, whereas other parts of New Zealand are really struggling with this weed.
"We are literally having to go into people's gardens and remove this beautiful purple plant from their gardens to stop the spread into nature."
Boxthorn, field horsetail, smilax and German ivy are also on the hit list of pest plants Environment Southland is trying to get on top of, she said.
"Plants like smilax and German ivy, both creepers that, once again, are in really low numbers here in Southland, and we want to get rid of them.
"Because if you visit places up in Northland, German ivy is just everywhere, climbing over all the native plants and destroying the ecosystems that our precious natives are living in."
There is a national pest plant accord with about 150 plants that are banned from sale or distribution in New Zealand, she said.
"Then each regional council has a regional pest management plan that has different plant species on it that they want to keep out from their region because they've seen the devastating effects elsewhere."
In some cases, such as eradication plants, you can't even have them on your property, Hazley said.
Other pest plants such as cotonester and Darwin's Barberry are allowed but are a serios threat if they escape from gardens, she said.
"We would prefer that you remove them and definitely do not share them around."
There are any number of ways people might be selling or swapping these pest plants, she said.
"People are literally going into the garden going, Oh, this plant's popped up. I've got 10 extra plants. Oh, I'll pop them up and sell them.
"But often those ones that are growing really well and they're spreading really well are actually pest plants or weeds."
It's hard for regional councils to keep an handle private sales, she said, and more concerning was when a commercial nursery was found to be selling a wilding pine.
"Pinus mugo is in our Regional Pest Management Plan, you're not allowed to sell it and spread it, because it's very good at spreading itself.
"And unfortunately, a nursery was selling pinus mugo - in other areas in New Zealand, you can actually sell it, whereas in Southland, we're like, no, no, definitely not."
Home gardeners should first identify a plant before thinking of selling or sharing it, and pest plants in the garden should be disposed of carefully, she said.
"Be really careful about where those seeds go, sometimes the best thing is just getting a good old plastic bag and double bagging things and making it so that those seeds will never see the light of day."
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