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The problems began soon after Bennett’s wallabies from Tasmania were taken to The Hunters Hills in the Waimate District in 1874 for recreational hunting.
Their population boom led to damaged farm pasture, crops and fencing, and native bush and forestry plantings.
A 2017 Ministry for Primary Industries report predicted the cost to the economy of not controlling wallabies in the South Island could be $67million within 10 years.
Anecdotal reports say the numbers are increasing again in the Waimate area. Many farmers are upset about it, but few would go on the record.
Walter Cameron had no such qualms. He has been dealing with wallabies at his family’s 3900ha Wainui Station, near Hakataramea, for most of his life and knows how to keep them in check.
"The family has been here for 110 years," he said.
"The wallabies turned up in about the 1950s."
The pests were known to be in the Waimate Gorge when he was a child, and had since spread into a much wider area.
A wallaby board used to be responsible for managing the marsupials and landowners were charged a specific wallaby rate.
But circumstances changed.
The board was disbanded in the 1990s, and once calicivirus arrived to control rabbits, use of the 1080 poison that was used to kill them diminished.
"That’s when the wallaby population started to explode," Mr Cameron said.
Wallaby numbers had been "way down" in the board’s days, and he was worried all the expertise its members had built up was lost. They had become experts on the wallabies’ habits and breeding patterns, and therefore on when and how to cull them.
About 3000 wallabies were shot on his land each year. He hired a professional shooter with heat-seeking technology to kill wallabies and rabbits.
"We started off using rig shooters. It wasn’t working.
"We used a chopper but it wasn’t making any hole in them."
Mr Cameron said he spent $15,000 to $20,000 a year on wallaby control.
A poisoning programme for his area was set up about five years ago, but the situation was "very tricky", he said.
One neighbour was not keen on the use of 1080 poison and did not want part of his farm taken out of use for several months as part of the programme.
"We tried Feratox [encapsulated cyanide] and other poisons, but the wallabies still increased. That’s why we went to 1080."
Mr Cameron said he and one neighbour went ahead, with consent from Environment Canterbury, the authority responsible for wallaby control.
The 1080 needed to kill wallabies was 10 times stronger than that used on rabbits.
When the rabbit poisoning was still in force, it used to kill the juvenile wallabies, Mr Cameron said.
"One of the biggest issues is the right development of the right-size pellet, so it could break down quicker.
"It’s like a big sheep nut.
"We’re getting 99.9 per cent kills. It’s blown them out."
He believed the neighbour who participated in the 1080 programme would continue to do so, having seen the benefits.
"1080 gets the resident population."
There was now "real danger" of wallaby numbers becoming uncontrollable, Mr Cameron said.
He had made repeated submissions to ECan saying a co-ordinated kill was needed for an effective drop in numbers.
"It is a futile exercise for one property to undertake a poison unless neighbouring/adjacent properties undertake the same."
He said ECan should encourage the formation of farmer cluster groups and punish those who did not control wallabies on their land.
"They’re not strong enough on compliance."
Mr Cameron estimated 3000 wallabies on the farm were the equivalent of about 1400 sheep.
"They foul it and take all the best stuff."
Wallabies were also prolific breeders — they could have a joey in their pouch and be pregnant with another. And when their population dropped to near extinction, they bred even more abundantly.
Getting rid of wallabies was an economic necessity for Wainui Station, he said.
"We had to do it. It was costing us money."
It was more economic in terms of return per hectare to pay for the poisoning than not to, he said.
"We can run more stock."
Mr Cameron wanted the wallaby board to be brought back as a specialist group that could act where populations were getting out of hand.
He appreciated the subsidy available from ECan and felt it was money well spent.
"It actually does affect everyone. There are environmental issues with tussocks and scrubs and there’s s... in the waterways."
ECan biosecurity regional leader Graham Sullivan said the status quo approach to managing wallabies had to change — "as identified by Walter Cameron".
"Wallaby are spreading across New Zealand at a greatly increased rate," Mr Sullivan said.
"If we don’t address the problem now, it is conservatively estimated that approximately a third of the North and South Islands will be populated with wallaby in the next 50 years.
"The current economic impact of wallaby is estimated to be approximately $28 million per annum. If they continue to spread at estimated rates, this could grow to nearly $84million p.a. over the next 10 years and continue to increase beyond this."
Mr Sullivan said representatives from farming, regional councils, Crown agencies, the Ministry for Primary Industries and others were developing a national plan for wallaby management. A business case for Crown funding help had been prepared.
"Regional councils have increased operational budgets significantly, but this alone will not fund the cost of operational activity at the scale required nor the research costs for new control and detection tools.
"Meanwhile, our effort at Environment Canterbury is focused on stopping the spread of wallaby from within the containment area and locating those that have escaped and established outside."
The Budget announced last week included $315 million earmarked for biosecurity including weed and pest control. That included $27 million for the Ministry for Primary Industries to get populations of wallabies in the Bay of Plenty, Waikato, Canterbury and Otago under control.
Agriculture Minister Damien O’Connor said wallabies posed a threat, economically and environmentally.
"They are a growing threat to farmers because they compete with livestock for food. Three Bennett’s wallabies can eat the equivalent of one 50kg sheep. They can also destroy agricultural crops and plantation forestry and damage fences."
The spread of wallaby populations was creating additional pressures for agriculture, forestry and conservation. The initiative would build on existing efforts to knock the population back, he said.