A possum control programme in the Silver Peaks, north of Dunedin, is dependent on the vagaries of the weather.
Animal Health Board Southern South Island programme manager Brent Rohloff said the control job was to reduce the spread of, and attempt to eliminate, bovine Tb in the area's possum population.
However, the contractor, the Otago Regional Council's regional services division, was waiting for a "reasonable weather window" which was a difficulty in the Silver Peaks, he said.
The two-stage programme involved a pre-feed being put out and the toxin 1080 about one week after that, spread by helicopters using "extremely sophisticated GPS".
The reserve would be closed on the day of the operation and the day after, with staff stationed at its entrances and signs in place advising of the closure.
The job had to be completed during winter as the board only had permission from Public Health South to carry out the programme until the end of August. However, it would not be compromised just for the sake of getting it done.
"The main reason we do it in winter is the feed is lower in the bush so the possums are more likely to take the bait and it's a high recreation area in summer," Mr Rohloff said.
The work would not be carried out at the weekend or on public holidays.
