The Resilient Forests Programme has turned a poorly understood threat into something manageable, bridging the gap between research and on-the-ground decision-making for red needle cast, a relatively recent, high-impact needle disease of radiata pine. Through coordinated field trials, modelling and tool development, the programme has turned complex research on disease impacts, environmental drivers and control strategies into practical tools, giving foresters greater confidence in managing RNC.

The challenge

In the early 2000s, a new forest disease emerged in New Zealand – unseen anywhere in the world previously. The disease had no name, no known cause and no management strategy.

After its discovery, early research characterised the disease symptoms and identified the causal agent. We now know red needle cast (RNC) is caused by the aerial pathogen Phytophthora pluvialis. Although the pathogen has since been found in the USA and very recently in Europe, it is only in New Zealand that it impacts radiata pine. As a result, there is little relevant global information to inform management strategies. Early research with US collaborators confirmed that Phytophthora pluvialis was native to the Pacific Northwest of the US and identified potential pathways of introduction to NZ – which MPI have since tightened. Research then demonstrated that there was little risk of transporting the pathogen on exported logs – reassuring our international trading partners, protecting market access and addressing a major early concern from industry. RNC can develop rapidly but then seemingly disappear. Outbreaks can be localised. This unpredictability complicates both management strategies and the research required to develop them.

When the Resilient Forests Programme began in 2019, the industry had:

1. growth impact data from a single RNC disease outbreak in one forest, with no knowledge of cumulative impacts over a rotation
2. a framework for an epidemiological model to predict disease, but not the data required to parametrise, calibrate or validate it
3. evidence that low-volume copper fungicide could reduce RNC severity, but no efficacy data under high disease pressure, no cost-benefit analysis, and no way to recommend when or where preventative control was needed. This left the industry facing a potentially high-impact but poorly understood disease, without the knowledge required to guide its management.

What we did

We redefined industry’s understanding of RNC, moving from limited site-specific observations of the disease to comprehensive knowledge of impacts, drivers and control strategies.

We have quantified the growth impacts of RNC to enable cost benefit analysis of management activities, determined the environmental drivers of disease outbreaks to enable foresters to predict when and where they would occur and when intervention would be required, and identified effective controls to reduce disease severity and impact.

Development of tools for application to both research and operational disease management has been crucial. This includes remote sensing methodologies for disease monitoring, diagnostic tools for pathogen detection, and sensor networks for environmental monitoring that feed real-time data into risk models that allow disease prediction.

We have maintained and established long-term field trials and infrastructure enabling us to assess disease impacts across a full rotation, obtain data to calibrate and validate predictive epidemiological models underpinning RNC risk decision support tools for foresters, and evaluate the efficacy of copper fungicide for control of RNC under severe disease pressure.

Based on current models, and at the worst case, we now know:

• Each severe RNC outbreak can reduce radial growth by up to 31% over 3 to 4 years. Recurring disease outbreaks every three to four years reduced radial area growth by 20% over a rotation, equivalent to a loss of up to 215 m3 ha-1 (16 %) volume and $21,688.75 ha-1 (17.3 %) value.
• How environmental factors (temperature and moisture) impact each stage of the RNC disease cycle.
• Low volume applications of copper fungicides at the same rate used to control Dothistroma reduce RNC. But sprays must be timed right – as they are preventative rather than curative.

The RNC Regional Risk Forecasting tool can be accessed at the FGR website. This digital tool provides a regional scale indication of the likelihood of an RNC outbreak, based on recent weather conditions. It is designed to help foresters understand when environmental conditions are becoming favourable for disease development.

What has changed so far?

Foresters highly value the foundational research carried out within the Resilient Forests Programme.