Four poisoned pohutukawa trees which arborists believed would almost certainly die are showing promising signs of life after a new kind of treatment.

In November last year, Opito Bay residents were horrified to discover four beachfront pohutukawa were riddled with drill holes and appeared to be dying. The ground was littered with dead leaves and several large branches were bare.

The trees were not only valued for their shade and flowers but also for their history. Many residents at the picturesque bay near Kerikeri were descended from Ralph Rowsell, who was thought to have planted the trees 50 years ago.

An arborist confirmed the trees had been poisoned and were most likely doomed.

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However, a treatment applied over the past seven weeks by a soil and plant nutrition expert appeared to be working wonders.

Phil Walesby, who returned to New Zealand in 2015 and now lived in Kerikeri, used the drill holes to administer his own formula six times before sealing the holes with beeswax.

Phil Walesby inspects new growth on a poisoned pohutukawa at Opito Bay. Photo / Peter de Graaf
Phil Walesby inspects new growth on a poisoned pohutukawa at Opito Bay. Photo / Peter de Graaf

He also had the foliage sprayed with the same formula and applied a soil conditioner around the trees.

Walesby provided the formula without charge while the Far North District Council covered the costs of the arborist and the cherry picker to carry out the spraying. The trees were due to be sprayed once more this Friday.

When the Advocate visited the bay this week, all four trees were showing fresh growth from the branch tips and new shoots were sprouting from the trunks. That was not seen on trees which had not had the treatment.

Walesby said he was shocked when he read a newspaper report about the poisoning and then visited Opito Bay. He figured there was nothing to lose by trying his formula.

''Trees are a thing of beauty, and when I talked to locals I could sense these trees were like children to them.''

A new shoot springing from the trunk of a poisoned pohutukawa at Opito Bay. Photo / Peter de Graaf
A new shoot springing from the trunk of a poisoned pohutukawa at Opito Bay. Photo / Peter de Graaf

Walesby previously used a similar formula, which he called Biohumik, on a crop of cow peas in India which had been accidentally sprayed with glyphosate. The crop recovered within a fortnight.

He had also worked in Italy on grapevines affected by fungus Esca and olive trees attacked by a pathogen with similar effects to kauri dieback.

Walesby believed his formula worked by clearing metabolic pathways blocked by herbicides such as glyphosate.

While some branches on the Opito Bay pohutukawa had died he was confident the trees would recover fully.

Council infrastructure manager Andy Finch said the council was grateful to Walesby and thrilled his treatment had provided new hope for the trees. The council had since improved surveillance at the reserve and urged locals to be vigilant.

All trees on public reserves were protected by the Reserves Act and the Resource Management Act, and anyone caught damaging them would be prosecuted, he said.

Meanwhile, police are still investigating. Anyone with information who has not yet spoken to police should call Senior Constable Rhys Dempster at the Kerikeri station on (09) 407 9211 or Crimestoppers, anonymously, on 0800 555 111.