Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Defoliation of Eucalyptus regnans: Barron Road Syndrome (BRS)
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 101, October 2000.
Barron Road syndrome (named after the first study site), affects some of the ash eucalypts and is characterised by the abscission of new foliage, with the upper crown of badly affected trees gradually becoming totally devoid of leaves. Emerging leaves exhibit small necrotic spots with shoots, stems, and petioles often roughened with small galls. Older leaves may also be distorted and exhibit extensive leaf spotting and galling. A suite of fungi have been found associated with the affected tissues of young trees - these include Aulographina eucalypti, Elsinoe eucalypti, Mycosphaerella cryptica, M. swartii, Pseudocercospora eucalyptorum, and Colletotrichum sp. As the trees age, the variety of fungi on leaves and shoots declines with A. eucalypti becoming dominant. Badly defoliated trees cease to grow and, in locations where the disease has been most severe, many trees have died.
Barron Road syndrome particularly affects Eucalyptus regnans - other species (E. fastigata, E. delegatensis in particular) may exhibit, some of these symptoms but generally retain most of their foliage. Plantations in the central North Island where rainfall can exceed 2000 mm p.a. have been most severely affected, with the humid gully plantings and north facing slopes exhibiting the highest disease levels. An extremely wet spring in 1989-90 led to massive defoliation of several thousand hectares of E. regnans , whilst adjacent stands of E. fastigata , although spotty, retained most of their foliage. Decline of E. regnans and E. delegatensis , characterised by poor growth, crown dieback, and some mortality, in the larger plantations in the central North Island has been ongoing since the early 1980s. Both species originate from areas in Australia with a distinct winter rainfall pattern. Seasonal distribution of rainfall is an important aspect of site adaptation for many of the eucalypt species. Although rainfall data for the affected New Zealand locations show that from 1971 through to summer 1979 there were consistent winter rainfall maxima, subsequent uniform rainfall distribution patterns have occurred with some summer peaks. Transfer of eucalypt species from winter to summer rainfall areas is usually unsuccessful but this lack of adaptability may have been disguised in the 1970s. Eucalyptus fastigata , planted alongside the BRS-affected E. regnans and generally unaffected (extensive leaf spotting but little foliage loss), comes from an area with a more uniform rainfall pattern. Consequently E. fastigata is better adapted to withstand the onslaught of fungal attack that occurs when temperatures are moderate to warm and there is plenty of moisture available. Biocide trials carried out on young E. regnans showed that regular (3- to 4- weekly) applications of a broad-spectrum fungicide gave reasonable control of the condition. Because such frequent spray schedules are not a practical option for control of diseases in plantation forestry, the immediate strategy has been to make a shift in species/site matching with E. regnans no longer planted in locations where this species was badly affected.
(Margaret Dick, Forest Research)
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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