Emily McLay and Dr Stuart Fraser next to a stand of pine trees affected by red needle cast. Photo / Stephen Parker Photography
Emily McLay and Dr Stuart Fraser next to a stand of pine trees affected by red needle cast. Photo / Stephen Parker Photography
New research and smart technologies are offering hope and solutions to foresters waging war against a silent enemy in our pine plantations.
Red needle cast (RNC), an unyielding fungal-like disease, has silently been wreaking havoc on pine trees in New Zealand since at least 2008.
Infections cause pine needles to lose their colour and fall to the ground, with research showing how defoliation can impact growth for three years after the trees show symptoms.
Scientists from Scion’s Resilient Forests Research Programme are at the forefront of the battle.
Dr Stuart Fraser, the leader of Scion’s Ecology and Environment research group, has been investigating the disease and potential control strategies for over six years.
Forest pathologist Emily McLay joined Fraser in 2021 to add depth to the understanding of the disease with research that aims to make it easier to predict when outbreaks will occur.
La Nina events affecting New Zealand in recent years have resulted in extreme wet conditions.
This increased moisture has created a favourable environment for needle diseases, making them more widespread and persistent.
“We used to believe in disease seasons, but recently, these seasons have become continuous due to the prolonged wet conditions.
McLay said that normally, drier and hotter weather would interrupt the disease cycle, but with the persistent moisture, RNC had continued to thrive, contributing to this year’s severity.
Satellite imagery of plantation forests on the East Coast, provided by Indufor, illustrates the extent of the disease this August, compared with the same time one year ago.
Dr Stuart Fraser, the leader of Scion’s Ecology and Environment research group, inspects pine needles for red needle cast under a magnifying glass. Photo / Stephen Parker Photography
Scientists say the key to combating RNC lies in deciphering the pathogen-host interaction and how the environment influences it.
RNC completes its life cycle on the needles of radiata pine trees, and very quickly responds to environmental stimuli.
McLay’s laboratory work is focused on understanding how temperature and moisture drive different processes in the disease cycle.
“It’s a targeted study that we can use to build epidemiological models, so we can predict when these big years might happen.”
Co-variation was one of the challenging aspects of field trials, she said.
“Winter is typically colder and wetter, whereas summer is warmer and drier.
“When it comes to building a model, it’s really hard to pull those apart.”
Forest pathologist Emily McLay’s research aims to develop a model to predict red needle cast disease outbreaks. Photo / Stephen Parker Photography
McLay’s research, therefore, focuses on teasing out the influence of temperature and wetness, shedding light on their distinct roles.
To help the forestry industry and Scion’s pathologists better understand the extent of RNC, Scion’s remote sensing and geospatial intelligence team provides monitoring support.
Scientists are mapping the presence of the disease and are keen to hear from industry professionals with suspected sightings of RNC to better inform their model.
Team lead Grant Pearse said they used free, coarser resolution satellite imagery to identify areas that might have disease expression.
“But it can generate some false positives for various reasons.”
He said RNC’s presence could only be confirmed through the purchase of very high-resolution satellite imagery, from a commercial provider, for more detailed mapping.
He said Scion “would love to hear more from industry” about areas where RNC could be impacting forests, as it would use the commercial imagery budget efficiently and make modelling more accurate.
“Having more accurate data means we’ll need to investigate fewer false positives long-term.
“Ideally, we are looking for larger areas of trees affected by RNC as satellites struggle to detect a few roadside trees, for example.”
As the RNC battle escalates, pragmatic solutions for industry are imperative, with copper emerging as a viable control treatment.
Already used in low doses to manage Dothistroma needle blight, a disease akin to RNC, copper’s efficacy has been validated for more than 60 years.
The Central North Island, considered a hotbed for Dothistroma, saw the first copper trials to control RNC in 2017, led by Fraser.
Significant RNC outbreaks in 2015 and 2016 spurred Manulife Forest Management (NZ) national forestry manager Mike Baker to collaborate with Scion on large-scale copper trials.
Satellite images from August 2022, before red needle cast affected East Coast forests. Photo / Supplied / Scion
Trials in Kinleith Forest demonstrated that copper significantly curbed RNC’s severity.
These trials explored optimal spray timings for RNC control. However, a consistent pattern wasn’t evident.
Despite this, disease severity decreased across all trial timings compared to unsprayed control.
It’s hoped copper trials on forests on the East Coast will shed more light on the effectiveness of copper under greater disease pressure.
With the Resilient Forests Research Programme developed to future-proof planted radiata pine forests from the impact of climate change, McLay’s research is building towards the development of a prototype model to predict RNC disease outbreaks.
Although a few years away from being commercially available, the tool’s aim is to give foresters information they can use to take pre-emptive action.
With satellite monitoring and copper research, a transformative disease management approach is emerging, McLay said.
Satellite images from August 2023 illustrate the impact of red needle cast on East Coast forests. Supplied / Scion
“We’re aiming to not just respond to outbreaks, but foresee and address potential concerns.”
Forest Growers’ Research chief executive Paul Adams said the research on the potential use of copper treatment was “promising”.
“Combined with the development of predictive models and satellite-based monitoring, these research efforts will help our future forests be more resilient in the face of climate change.”
