Farm Forestry New Zealand

PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

The nectria research programme

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 147, December 2004.

A stem malformation problem has arisen following pruning in Pinus radiata plantations in Southland and Otago, associated with infection by a fungus named Nectria fuckeliana. Symptoms take the form of longitudinal depressions (fluting) or cankers extending above and below the pruned whorls. The Forest Health Group at Forest Research first became aware of this disorder when samples were received late in 1996, although stem malformation had been seen in southern forests since the mid-1980s. The canker symptoms are very similar to those of “Diplodia whorl canker”, and the fungus Sphaeropsis sapinea was isolated from damaged stems on several occasions (Forest Pathology in New Zealand 1: 1–4). However, although S. sapinea is known to invade through pruning wounds, further investigation revealed that it was present at only a low incidence in southern forests, and the majority of stub infections were by N. fuckeliana. Due to a confused taxonomy, the formal identification of this fungus was not confirmed until March 2003.

Forest Research has been conducting significant research on the Nectria-associated disorder since 2002. The research programme was initially funded by a Nectria Working Group (NWG) composed of a consortium of several forest companies (Blakely Pacific, City Forests, Ernslaw One, PF Olsen & Co., Rayonier, and Wenita), which continues to fund a significant portion of the research. Latterly, the New Zealand Forest Owners’ Association has contributed additional funding through the Forest Biosecurity Research Council, and the Forest Health Research Collaborative has part-financed a regional incidence survey. In addition, supplementary funding for the Nectria Research Programme has been secured from the Foundation for Research Science and Technology.

The stem canker symptoms are often associated with sapwood staining and wood decay. As part of the initial research programme trees were felled, dissected, and whorl sections were closely examined in order to clarify this relationship and to determine the extent of the internal damage. It is also important to resolve the current distribution and potential spread of the disorder and to this end a series of surveys are now under way. Individual trees are being assessed in a variety of stands throughout the affected area in order to ascertain the incidence and severity of damage, and to determine whether symptoms are related to various environmental and physical factors such as altitude, climate, aspect, slope, seedlot, and silviculture. A more focused delimiting survey is planned for early 2005, in order to define the present distribution of N. fuckeliana in P. radiata stands in North Otago and South Canterbury. This will provide a baseline so that later surveys can monitor its spread. A wider national survey is being extended into the remaining part of Canterbury, the upper South Island, and Buller. Parts of the central North Island will also be assessed where seedlings from the southern region have been planted.

More needs to be learned about the fungus, and epidemiological and related studies will soon commence to examine the infection process, development, mode of spread, virulence, and relationships with environmental factors. Dr Patricia Crane from Alberta, Canada, has been appointed to a 2-year post-doctoral position to take up this work. An examination of the anatomical effects of infection and the formation of pathological heartwood will also be undertaken. To assist forest managers, a trial was initiated in late 2002 to investigate the effects of different pruning regimes and fungicide applications on pruned stubs. The future of this trial will be reviewed in November 2005, but early results are promising and the NWG is confident that research will lead to an operational management solution. Other work has been started to compare the relative susceptibilities of seedlings and cuttings, and the susceptibilities of other conifers will be examined early in 2005. All research is backed by an extensive review of the published literature. We are confident that the broad research strategy now in place will provide a long-term management answer to minimise the impact of this disorder.

(Lindsay Bulman and Margaret Dick, Forest Research)

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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)