The death toll includes the banksia and a large mānuka. A second banksia appears to be dying along with the tallest tree on the property, while a number of smaller mānuka have been cut down.
Harris said they had planted the banksias 25 years ago, five years after moving to Sullivans Rd from Switzerland. At that time their house was one of only two in the immediate area; now they are surrounded by top-end homes, many of them built in the past few years.
"I am maybe silly, it is romantic, but the trees are our babies, we pamper them. They take 20 years to grow, the birds come and they give us oxygen," Harris said.
They planned to leave the dead trees standing.
"We could cut them down and plant new ones but then they have won, they will have the view."
Gonin said the ground in the area was unstable clay.
"Without the trees it [the soil] will be gone. They take a long time to grow. It's a crime," he said.
The poisonings and the resulting suspicions have sparked something of a feud in the neighbourhood with residents, including the Swiss couple, issuing trespass notices against each other.
It's not new either. In 2005 a 20m-tall totara in their backyard was poisoned and had to be cut down.
A council spokesman said a staff member had investigated a complaint lodged on February 22 that trees had been poisoned on Sullivans Rd.
The trees, which were on both private and council land, were found to have drill holes. Some were already dead.
An arborist was due to inspect the trees this week due to concerns that one could damage a house if it fell. The poisoning has also been reported to Mid North police.
Meanwhile, an investigation into the poisoning of four beachfront pohutukawa at Opito Bay, near Kerikeri, is continuing. In November residents discovered the ailing trees' roots were riddled with drill holes. The council called in police in December after being unable to identify the culprit.
