Red needle cast (RNC) is shifting from an unknown threat to a disease New Zealand foresters can actively manage. The RNC Manual and RNC Regional Risk Forecasting Tool were released this month – marking an important stage in the management of this disease.

The RNC Manual provides an overview of the disease for foresters and guidance on how this knowledge may be integrated into disease management programmes.

The RNC Regional Risk Forecasting Tool and RNC Manual are outputs from the Resilient Forests Programme – co-funded by the Forest Growers Levy Trust and Bioeconomy Science Institute Maiangi Taiao. This research has combined long-term field monitoring, operational-scale field trials, controlled laboratory experiments, and modelling to quantify disease impacts, identify environmental drivers, and evaluate practical controls.

About the RNC Manual

Red needle cast (RNC), caused primarily by Phytophthora pluvialis, is a major foliar disease of radiata pine and Douglas-fir in Aotearoa New Zealand. Severe outbreaks can reduce annual radial growth by up to 50% and cause long-term productivity losses, particularly in high-risk regions, such as Gisborne. RNC severity varies strongly between regions and years, with wet, mild summer and autumn conditions often preceding major outbreaks. Stand structure also influences disease, with higher severity in dense stands and in cooler, wetter microclimates.

Over the past decade, research has clarified the disease biology, confirmed no trade risk from export logs, quantified growth and economic impacts, and identified the environmental drivers – especially temperature and needle wetness – that underpin outbreak dynamics. This work has enabled development of Aotearoa New Zealand’s first weather-based RNC infection risk model and an accompanying digital decision support tool that allows foresters to proactively track and manage risk.

Copper fungicide can reduce RNC severity when applied proactively at the right time, but reactive spraying is often ineffective due to logistic challenges and rapid disease development. Moderate heritability of resistance indicates genetic improvement is possible, though further field validation is needed. Remote sensing tools can support detection and monitoring at landscape scales.

This manual aims to provide the first comprehensive, end-to-end guide for understanding, predicting, and managing RNC using integrated monitoring, modelling, chemical control, breeding, and silvicultural strategies.

Read the RNC manual here.

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