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PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

The economic cost of dothistroma needle blight to the New Zealand forest industry

Scion is the leading provider of forest-related knowledge in New Zealand
Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

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

 

This information is intended for general interest only. It is not intended to be a substitute for specific specialist advice on any matter and should not be relied on for that purpose. Scion will not be liable for any direct, indirect, incidental, special, consequential or exemplary damages, loss of profits, or any other intangible losses that result from using the information provided on this site.
(Scion is the trading name of the New Zealand Forest Research Institute Limited.)

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