PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
THE ECONOMIC COST OF DOTHISTROMA NEEDLE BLIGHT TO THE NEW ZEALAND FOREST INDUSTRY
Back to Dothistroma needle blight
From Forest Health News 215, May 2011
Forest growers in parts of New Zealand consider Dothistroma needle blight to be one of the most serious diseases affecting growth of radiata pine. Currently the disease is controlled by aerial spraying of copper oxides. Silvicultural practices that promote airflow and remove susceptible individuals will also reduce disease. Areas are usually treated if the severity exceeds a threshold of 15%, as assessed from the air, but this varies among forest companies.
Past attempts to place a value on the cost of this disease to the forest industry have varied widely. In 1989 Geoff Sweet assumed volume loss due to Dothistroma was nil because disease was kept in check by spraying whereas Bulman in 2004 estimated loss to be $23 million per year. A modelling project undertaken by Scion has enabled the economic effect of Dothistroma needle blight to be estimated with reasonable certainty.
The modelling exercise, based on data collected from the forest health surveillance scheme, confirmed that severity was highest in moderately warm wet environments in the North Island and on the west coast of the South Island. In contrast, disease severity was lowest in drier eastern and southern regions of New Zealand. Severity increased to a maximum at a stand age of 12 before declining.
The total cost to the industry was estimated at $19.8 million per year and made up of three components. The cost of spraying was estimated at $3.8 million per year while growth losses in sprayed areas were estimated at $3.0 million per year. However, the largest cost component was $13 million per year which resulted from potential growth loss from areas with a severity lower than the 15% threshold for spraying.
The analysis highlighted the general issue of the severity threshold at which Dothistroma needle blight is controlled. Although lowering this threshold will increase costs this decision would need to be weighed against the volume losses in stands with low levels of disease.
Further research is needed to investigate this trade-off more closely. As the disease does not have a marked effect on stands with low final crop stocking it would be useful to investigate the effect of low disease levels on growth across a final crop stocking range.
For more detailed information see Watt, M.; Bulman, L.; Palmer, D. 2011. New Zealand Journal of Forestry 56 (1): 20-22.
Michael Watt, Lindsay Bulman, David Palmer
