Mount Maunganui's iconic Norfolk pine trees are sick and may be dying.

Two of the trees on Marine Parade have been struck with a mystery illness and will have to be felled if they do not recover, reports Tauranga City Council.

Norfolk pine trees along Marine Parade are sick.

A mystery pathogen is attacking the pine trees with this tree outside No.10 Marine Parade likely to go. Photo: TCC.

Other Norfolk pines along Marine Parade and along The Mall are showing similar signs of infection.

The mystery ailment comes on the heels of the summer drought, which hit the trees hard. Most of the pines recovered by April, but some are still showing signs of stress and may have succumbed to a mystery pathogen in their weakened state.

City arborist Richard Conning has called in Rotorua-based Scion Research, whose scientists have been investigating the state of the trees for the last couple of months.

Scion are currently analysing samples of foliage, roots and soil, and is putting together an extended sampling programme from both healthy and affected trees.

He believes the mystery pathogen has not been purposely injected into the trees.

'I haven't seen anything that would indicate there is poisoning like drill holes or dead grass round the base of the trees.

'I think it's pretty unlikely that it's poisoning, and the pathogen is showing itself in a number of trees spread out round The Mall and Pilot Bay area to varying degrees of severity.”

The affected trees on The Mall are not as affected as the Marine Parade trees, and most people might not notice anything wrong with them, says Richard.

It's hoped the sample analysis will identify whether a bug, fungus of virus is affecting the trees and how to treat it.

'They suggested doing some nutrient inoculations into the tree as well,” says Richard.

'It's just like a bit of dowelling, we drill a little hole in the tree and tap this dowelling in, and the tree can take it up from there. We are just sorting out exactly what composition we need and we will be getting that underway as soon as we can.”

Council staff say one of the Marine Parade pines is in critical condition and arborists are fearful that it won't pull through.

The trees along the beachfront are estimated to be 50-60 years old and expected to live another 60 years.

'The drought that we had was pretty severe,” says Richard.

'When a person gets run down they are subject to ailments, it's the same thing with a trees. They got run down by the drought and that has let the pathogen, or whatever it is, have more of an effect on the tree.

'They are pretty iconic, and we work hard not to lose them because they are such a landscape feature for the area.”