The experiment has varied the seasons when baits are put out, to find out whether that makes a difference. And it has looked for places where baiting is not done often, to make sure the animals are not bait shy.
Single cyanide baits will also be put out, if necessary, to kill possums that survive the 9g poison baits - and make sure Landcare staff can retrieve the radio collars.
There will be about four staff putting out baits and watching how possums react around Trains Hut in the Waitotara Conservation Area in late June and early July. They do the same thing in the Mangapurua Valley from mid-August to early September.
Mr Latham said they have permission to work over a large area in each place, but will choose a convenient smaller area away from tracks and private land to lay the baits.
He has placed large warning notices in the Wanganui Chronicle and there will be others on site. The carcasses of poisoned possums will be highly hazardous for dogs for up to six months.
The trial will finish by December 20, at the latest, and the result will be published in a report next year.