A breeding population of wallabies may already be established in the Maniototo, and if so, the impact on farmers is likely to be ''devastating'', Maniototo Pest Management (MPM) manager Ossie Brown says.
In addition to frequent signs and sightings of single wallabies on farms, he had seen scat of large and small wallabies together in two areas.
''If that is not a breeding population, I don't know what is,'' he said.
''I've been doing this for more than 46 years and this [the wallaby incursion] is the most serious thing I've seen.''
However, Environment Canterbury (Ecan) biosecurity team leader Brent Glentworth said he was not aware of any proof there was a breeding population in Otago.
He said Ecan was targeting the population on the Waitaki River's south bank, including using cyanide, 1080 poisoning and hunting.
Mr Brown said the pests crossed the Waitaki River via the Benmore and Aviemore dams and the Kurow bridge.
''They then come over the Hawkduns and see the Maniototo and think it is the promised land.''
Former MPM chairman Charlie Hore said he would like to see more funding and better barriers put in place.
Three wallabies had been shot in the Maniototo in the past six months, including one close to Ranfurly two weeks ago.
Should wallabies become established, the impact on farmers would be devastating, Mr Brown said.
''They are totally destructive. ''Three can eat as much grass as a sheep and they foul and sour the land.''
Mr Glentworth said he did not think the few animals that had been shot got into the Maniototo on their own.
He said they were likely to have been released by humans, probably hunters who had shot females and were reluctant to kill the joeys.
They were then raised as pets and were released or escaped.
Neither Mr Brown nor Wedderburn farmer Peter Hore believed the animals had been deliberately released in the Maniototo.
''I think it has the potential to be a massive problem and if they got established, wallabies would be [a big] threat to farmers, second only to foot and mouth disease,'' Mr Hore said.
MPM worked closely with the Otago Regional Council and was happy with the council's pest management.
Mr Brown would like to see a ''Judas'' wallaby used, which involves the capture of one animal, which is then fitted with a radio collar. The Judas animal was then released and led hunters back to his mob.
Ministry for Primary Industries (MPI) recovery and pest management manager John Sanson said the ministry did not fund the operational control of wallabies — that was handled by regional councils and landowners, but it was aware of the problem.
''We are working with regional councils, Doc, Linz and Landcare Research to identify ways to improve wallaby management in [New Zealand]. Federated Farmers North Otago provincial president and High Country industry group chairman Simon Williamson said he was concerned as numbers increased on the southern side of the [Waitaki] river. ''They are progressively getting worse and worse,'' he said.
One of the problems was individual farmers carrying out pest control, while their neighbours were not. He said there were reports of the pest moving into the Maniototo and he had also heard stories of hunters releasing them.
''God help anyone found letting them go.
''Three wallabies eat as much as a sheep and like Canadian geese, they foul the country.
''They are full of worms and not a particularly nice animal to have around.'' He said Ecan was committed to keeping the pest out of Otago. ''That is the last thing they want there.''