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PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Swiss needle cast on Douglas Fir

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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 165, August 2006.

A considerable amount of research has been undertaken in the past on Swiss needle cast disease of Douglas fir (Pseudotsuga menziesii) caused by the foliage-infecting fungus Phaeocryptopus gaeumannii. We know much about its life cycle in New Zealand, its distribution, and that it causes an average national volume growth loss of the order of 20%. Its importance in this country is almost certainly a result of the substantial spring rainfall levels at a time when the fungus is sporulating and infecting new flushing needles. However, it is apparent that the impact of Swiss needle cast varies regionally, and it is noteworthy, for instance, that more Douglas fir is currently being planted in the South Island where in broad terms stands appear healthier.

Phaeocryptopus gaeumannii is native and comparatively innocuous in north-western North America. However, since 1996 disease severity has been increasing in plantations in western Oregon, associated with growth losses of 20–50%. Researchers there have developed a model to predict disease severity based on mean daily winter temperatures and spring moisture, which accounts for 77% and 78% of the variation in 1- and 2-year-old needles, respectively. A collaborative project is now under way between Dr Jeff K. Stone, Oregon State University, and Ensis FBP, to develop a similar model for New Zealand. If we can explain the distribution of the disease in this country using climatic variables it is very likely that we can use a predictive model to identify regions where Douglas fir can be grown with least risk from the disease and where stands will be healthier and more productive.

Dr. Stone visited New Zealand in 2005, and field sampling was undertaken over 7 weeks between October and December at 16 sites throughout the country covering a range of disease severity and climate differences. The potential effect of genetic variation was controlled by limiting the sampling to three seedlots included in two 1996-planted New Zealand Douglas fir Breeding Cooperative trials situated at eight South Island and two North Island locations. These were supplemented with additional stands to ensure a full range of latitudinal and altitudinal variation.

Defoliation was assessed on a sample of trees at each site and measurements of infection intensity were made from counts in the laboratory of pseudothecia (fungal fruitbodies) blocking stomata in the needle samples.

It has been presumed that spread of P. gaeumannii in New Zealand originated from a single introduction of the pathogen in the North Island in the early 1950s. This is being tested, as part of the project, using microsatellite markers developed for P. gaeumannii in North America. A preliminary comparison between fungal collections from two widely separated sites in the North and South Islands, and North American fungal populations indicates that the two New Zealand samples are related to widely separated populations in North America, and therefore may represent different introduction events. A more complete microsatellite analysis of the New Zealand P. gaeumannii population is being conducted using 1400 single spore isolates which were collected simultaneously from the 16 sites. At present there are no data to hand.

However, initial results from infection and foliage retention data are very exciting. Greater casting of older needles occurs at some of the North Island sites, but higher altitude Karioi Forest is more akin to some of the better South Island locations. The infection index shows a strong positive relationship with winter minimum temperature.

These preliminary results suggest that a disease prediction tool for identifying areas best suited for cultivation of Douglas fir is feasible. The project is still at an early stage, and further field sampling is planned at additional sites and in different years, in order to strengthen the data set. The infection data will be modelled using climate values derived for each location from available GIS-linked climate models. The observed New Zealand infection data will be compared to infection levels derived from the climate-based disease prediction model developed for western Oregon as an independent validation data set for this model. Stepwise regression analyses will also be undertaken to determine which climate variables are most highly correlated with infection in New Zealand, and will include seedlot as an additional explanatory variable. A GIS-linked disease prediction map for New Zealand will be attempted based on the goodness of fit of the Oregon climate model and New Zealand climate data. If successful, this model could form the basis of a more dynamic model that could be used to predict changes in disease severity in response to climate change.

Ian Hood, Ensis;
Jeff Stone, Oregon State University;
Tod Ramsfield, Darren Kriticos, Ensis.

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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