Dieback bug kills pōhutukawa at Waiheke’s Matiatia Bay

A row of mature coastal pōhutukawa along the southern side of Matiatia Bay is slowly dying from a cousin of kauri dieback disease that is commonly known as root-rot.

Auckland Council biosecurity advisor Deryn Dromgoole says soil testing on the protected trees revealed several years ago thatPhytophthora multivora was present and likely to be involved in the dieback.

The deaths of the trees are now clearly visible along the shoreline.

Dieback is a symptom of Phytophthora infection that contributes to the decline of trees world-wide.

In a wet summer, species of Phytophthora living in soil and root tissue can produce millions of spores that affect a tree’s root systems.

Testing prompted by other dieback on the island ruled out Ohia dieback as the cause in May this year, Ms Dromgoole says.

It remains most likely that Phytophthora multivora is the culprit.

Tests have shown a cousin of kauri dieback, known as Phytophthora multivora or root-rot, is likely to be the cause of the deaths.

Auckland Council biosecurity team manager Ron Matthews says root-rot, which can be present in the ground for 30 years, has thrived in water-logged soil over the past couple of years.

“This is a fungal disease that takes off in the right conditions . . . it will kill the trees and there’s not a lot you can do.”

Mr Matthews says root-rot is endemic and is present across New Zealand.

“It’s well and truly established. It’s a very common disease in a lot of plants and is prevalent in certain areas.”

Root-rot affects more pōhutukawa every year, he says. “We’ve had an incredibly wet winter, as you know. It is just going to be more prevalent in some years than others.”

Mr Matthews says root-rot would have been exacerbated on Waiheke by extra ground water produced from increasing urban development.

Unfortunately for the trees, there is no known cure. “Generally speaking, it has been in New Zealand a long time, and that’s just the way it is.”

The dying trees are at Matiatia Bay where most visitors to Waiheke arrive by ferry. Photo: supplied