Anti-1080 protesters allegedly locked Auckland Council staff members in the Hunua Ranges Regional Park last night.
The council dropped 1080 in the ranges earlier today after an interim junction stopping the drop lapsed on Friday evening.
Auckland Council parks, sports and recreation manager, Mace Ward, said they were trapped in the park for more than an hour.
"We were able to remove those chains and exit the park safely and secure the park overnight. What also happened overnight we had graffiti on signage and some of our toilets and facilities."
Mr Ward said following today's drop, staff would now clear tracks and test water quality in the ranges.
The council was given the go ahead to drop the poison after the interim injunction lapsed on Friday evening.
The Friends of Sherwood Trust won a temporary injunction in the Environment Court halting the major pest control programme two weeks ago.
However, on Friday the court refused the Trust's bid to further halt the drop.
Mr Ward said the first block of the operation, which covers 16,000 hectares, was set to be completed today.
The pre-feed drop, which was completed before the drop was temporarily suspended, did not need to be repeated, Mr Ward said.
Following today's drop, staff will then work to clear tracks and test water quality in the ranges, he said.
On Friday, council staff phoned more than 100 households near the drop site to give them the required notice.
The action follows a recent spike in anti-1080 protests including one last week when dead birds were placed on the steps of Parliament, with activists claiming they were poisoned by the toxin.
However, after police were called in to investigate if the birds had in fact been bludgeoned, one of the protesters admitted some were actually road kill.
But a community board member said many residents in the Hunua Ranges did not oppose 1080 being dropped in the area.
Franklin Local Board member Malcolm Bell said no one wants to drop the toxin, but it needs to be done.
"We're in the situation where if we don't then wildlife, particularly the birds, are likely to be reduced drastically in numbers to the point actually where we probably won't have any native birds in the Hunua Ranges if we don't take action," he said.
There is a small minority of individuals in the area who oppose the drop, Mr Bell said.