Despite being a damaging foliar disease of Pinus species, little research has characterized spatial variation in disease severity of Cyclaneusma needle cast at a macroscale. Using an extensive data set describing Cyclaneusma needle cast (Ssev) on plantation-grown Pinus radiata D. Don stands distributed widely across New Zealand, the objectives of this research were to (i) develop a regression model describing Ssev, (ii) use this model to identify key drivers of Ssev and their functional form and relative importance, and (iii) develop spatial predictions of Ssev for New Zealand P. radiata under current climate. Using an independent validation data set, the final model accounted for 73% of the variance in Ssev using four significant (P < 0.001) explanatory variables and an isotrophic exponential model to account for the spatial covariance in the data. Ssev was most sensitive to elevation followed by mean winter air temperature, mean relative humidity during July, and then stand age. Ssev increased to a maximum at mean winter air temperatures of between 7 and 9 °C before declining. Relationships between Ssev and all other variables were linear and positive. Spatial predictions of Ssev varied widely throughout New Zealand. Values of Ssev were highest in moderately warm, wet, and humid high-elevation environments located in the central North Island. In contrast, relatively low values of Ssev were predicted in drier eastern and southern regions of New Zealand.
Type specimens of Streptaxidae from Henry C. Burnup in the collection of the Museum of New Zealand Te Papa Tongarewa