Dothistroma needle blight: a brief review and estimation of the potential hazard in Victorian radiata pine plantations.  I. O. Cook.  December 1985.  12 pp. (unpubl.)

SUMMARY

Dothistroma septospora (Dorog.) Morelet a northern hemisphere, ascomycete infects pine foliage sometimes causing a disease referred to as Dothistroma needle blight. In the Southern Hemisphere it has caused serious defoliation in exotic pine plantations, and in some parts of East Africa, highly susceptible species, such as Pinus radiata D. Don. (radiata pine), have been replaced by more resistant, less productive pines. In New Zealand aerial spraying with copper fungicide is used to protect many susceptible plantations.

The fungus was first discovered in Australia in 1975 in northern New South Wales where it has caused serious defoliation in some P. radiata plantations. It was first observed in north-east Victoria in 1979, where damage has been confined to radiata pine growing in low lying gullies and flat depressions.

Warm wet weather promotes infection and, in Australasia, it is generally accepted that rainfall over 100 mm per month and mean monthly temperatures of 10-20°C encourage disease development. Disease symptoms are easily recognisable. The foliage turns reddish brown, needles of all ages are attacked and reddish coloured bands containing small, erumpent, black fruiting bodies are formed on the needles. Tree death is rare, but repeated defoliation of over 25% of the crown can reduce diameter increment. Defoliation at levels of about 50% halve diameter increment while height growth is reduced at higher levels of defoliation. In New Zealand, radiata pine generally becomes resistant to the disease at an age between 14 and 20 years, but this phenomenon has not yet been observed in Australia.

Calculation of Dothistroma hazard ratings, for major Victorian plantation regions, based on total monthly rainfall and mean monthly temperature, indicate that the potential importance of the disease in most Victorian plantations is likely to be much lower than in New Zealand. Highest hazard ratings are given to plantations located in parts of the Otways, north-eastern Victoria, and South Gippsland, and plantations in these regions may require regular surveillance and occasional control spraying to maintain productivity. However, within these regions, disease distribution is uneven, with worst damage being confined to low-lying areas where microclimate favours the disease.

Also published:

Marks, G.C., Smith, I.W. and Cook, I.O. (1989)  Spread of Dothistroma septospora in plantations of Pinus radiata in Victoria between 1979 and 1988.  Aust. For. 52: 10-20.