Reduced fungicide use in the nursery improves post-planting productivity of Pinus radiata for at least six years

Abstract

The fertilisers and fungicides used in tree nurseries to stimulate growth and provide disease protection are an important component of conventional nursery management. However, it has been demonstrated that the ectomycorrhizal (ECM) fungi associating with Pinus radiata D. Don seedlings in the nursery can be significantly affected by increasing exposure to these products, driving reductions in the relative proportion of the ECM species most positively correlated with seedling nutrient uptake. Increasing fungicide exposure was also shown to reduce seedling size. To determine the significance of these effects on post-nursery performance, 2592 P. radiata seedlings were randomly selected from within treatment plots in this nursery chemical exposure trial and established at a site in Kaingaroa Forest, New Zealand. Assessments of the ECM community present on the trees in the plantation determined that after two years there was no longer any effect of the nursery treatments, likely due to the homogenising effect of the site conditions. Over six years the performance of the trees in the plantation was not affected by the extent of fertiliser application during their time in the nursery, but decreased nursery fungicide use had slight positive legacy effects on both tree survival and diameter growth. These gains combined to produce a significant increase in plot level basal area with reduced nursery fungicide use. Further analysis incorporating the effect of thinning on stand dynamics reinforced the potential gains in the forest from reduced fungicide use in the nursery, and the lack of benefit from fertiliser use. Based on the data collected following trial establishment, it was concluded that the observed differences in tree performance were likely driven by the impact of the ECM communities initially associated with the seedlings at planting. While the authors strongly recommend any reductions in P. radiata nursery fungicide use be considered carefully due to ongoing issues with fungal pathogens in these monoculture systems, the potential for improved nursery and plantation performance is significant and should be explored more widely.