A month-long poisoning operation will cover more than 23,000ha in the Teviot Valley.
The possum control programme is directed by Ospri New Zealand and carried out by Leith Contractors.
The ground-based programme was being carried out as part of the national TBfree programme and sought to eradicate tuberculosis from the Teviot River area, Leith Contractors owner Tony Leith said.
It would cover 23,183ha from Roxburgh East northeast to Pinelheugh, east to the western shore of Lake Onslow, south to Mt Teviot and west to the Teviot River; then follow the east bank of the Clutha River back to Roxburgh, he said.
Pre-feed pellets were laid last week and poison - Feratox (potassium cyanide) capsules and cyanide paste - would now be laid for about three weeks, hand-laid on to the ground or attached to trees. No poison would be laid within 20m of waterways.
Traps would be used in forestry areas, and other non-kill traps would be placed up trees near residential areas, Mr Leith said.
Residents are being advised not to touch baits or poisoned carcasses, and to keep pets and children supervised.
