Auckland water reservoirs could be in the firing line of an extended painted apple moth spraying programme, papers show.
The Government yesterday announced it would spend another $90 million trying to eradicate the painted apple moth, despite an expected success rate of only 60 to 80 per cent.
The three-year eradication programmewill involve extending the current aerial spaying programme to between 8000 and 12,000 hectares covering Auckland suburbs such as Henderson, Te Atatu, Glen Eden, New Lynn and Point Chevalier. Between 117,000 and 165,000 people live in the increased spray zone.
A previous $23.3m programme had failed to wipe out the pest, which was discovered in 2000 and could cost the nation $58m to $356m over 20 years.
Cabinet briefing papers warn the extended programme could result in the biological insecticide Foray 48B, or Btk, getting into water reservoirs.
"Btk is very sensitive to chlorination and is inactivated in a short time by standard water treatment practices," the papers said.
"However, there could still be problems relating to public perceptions of possible health risks arising from the spraying of drinking water sources.
"Should spraying near reservoirs be required, these perceptions could be partly managed through a post-spraying stand down time, as not all reservoirs would be sprayed in the same cycle."
Cabinet approved the programme despite Treasury advice which warned $90m over three years, plus the $23.3m already spent, could not be justified on economic grounds.
"Given the history of spread of the painted apple moth, the cost over-runs of significantly small eradication attempts, the estimated 20-40 per cent chance of failure attributed by the technical advisory group to any future, we remain doubtful about the feasibility of this programme," Treasury said in the briefing paper.
Treasury also believed the economic effects of the painted apple moth establishing were likely to be towards the lower end of predictions.
However, Biosecurity Minister Jim Sutton said it was a "beast" which posed an incalculable threat to indigenous forests.
"Technical advice is that eradication of the painted apple moth is still possible, despite larval finds outside the current zone," Mr Sutton said.
"Cabinet has decided to go ahead with another eradication attempt to try to achieve this."
Spraying will be done at three-week intervals and starts in October.
