Dieback of pine needles on a pine plantation near the top of the Pahiatua Track prompted Pahiatua resident Ross Cotter to ask why the trees are dying.
Pahiatua arborist Kevin Nicholson observed the dieback three years ago.
"It's affected both younger pine trees and old man pine and has spread south as far as Mangamaire," he said.
It is likely to be a disease called red needle cast caused by a micro-organism called Phytophthora pluvialis, according to Robert Taylor, senior scientist for Ministry for Primary Industries.
"It has been present in New Zealand for many years and is really common throughout the North Island. This area has been sampled many times for this disease."
Red needle cast:
Unexplained needle cast events in pine trees have been seen in planted forests in New Zealand since at least the 1950s, according to Scion, formerly New Zealand Forestry Research.
In May 2008, a routine forest surveillance check on the East Cape found green needles with unfamiliar dark bands or lesions. Researchers visited the site and named this potentially new disease red needle cast (RNC), based on the needles turning red and being easily detached.
An unknown species of Phytophthora was confirmed in needles collected from the affected trees. In 2012, DNA sequencing matched it with Phytophthora pluvialis, a newly-described species from Oregon, USA.
Managing red needle cast:
Phosphite fungicidescan control the disease. According to Farm Forestry New Zealand, in parts of New Zealand shelterbelts, woodlots and commercial plantations suffer from Dothistroma needle blight, Cyclaneusma needle cast, physiological needle blight (PNB), or red needle cast (RNC).
In some regions all four diseases are present. Many factors, some still to be confirmed, contribute to outbreaks - rainfall, temperature, tree age, silvicultural treatment.
Dothistroma needle blight can be controlled by applying a copper fungicide in October or November. Cyclaneusma is more difficult to control. Susceptible trees can be removed during thinning operations if thinning is done when the disease is showing.
Control of needle diseasedepends on correct identification.
"At this time of the year we do get many reports of pine trees experiencing dieback and previous samples taken from this area have not detected a new disease of biosecurity concern," Rob Taylor said.
"There are also many other physiological, nutritional and pest disorders that cause pine dieback."