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ItemDiplodia pinea (Desm.) kickx, a parasite on Pinus radiata D. Don(University of Melbourne, 1957)Since 1911 foresters have associated a fungus* Diplodia pinea (Deem.) Kickx., with a disorder of introduced conifers in Australia (Birch, 1936), This disease has been variously described by foresters here as "die-back", "autumn brown-top", "dead-top", or "red-top". The upper part of the crown dies back at least three or four feet, and the needles assume a red-brown colour which contrasts sharply with the green tops of neighbouring healthy trees. Various species of Pinus show similar symptoms, which, however, may be traced to other causes. For example, in South Australia, Stoate (1950) applied the term "die-back" to the deficiency disease corrected by adding small quantities of sine. Stoate used the term "autumn brown top" for another disease which had been described as "dead�top" in Victoria and the Australian Capital Territory, and was attributed to summer drought (Waring, 1951; Millikan and Anderson, 1953). In New Zealand, Birch (1936) gave the name "red-top" to the effect of Diplodia on Pinus. As there has been so much confusion in the use of vernacular names to describe disorders of pines, it is proposed to use "Diplodia die-back" (Young, 1936) in connection with the disorder discussed in this thesis. In the Ovens Plantation of the Forests Commission of Victoria, in the north east of the State, Diplodia pinea is a suspected cause of die-back of mature pines. Although it has not yet been proved that Diplodia alone caused any deaths, the fungus is often associated with the die-back condition. It is, therefore, important to understand its relation to the health of Pinus radiata. Further, the possibility of a disastrous epidemic of the disease cannot he overlooked, because there have been outbreaks in other parts of the world which were far more severe than any yet seen in Victoria. For example, in 1932 In a sub-tropical part of South Africa, after three weeks of warm, humid weather following a severe hailstorm, 200 acres of 8 to 15 year old Pinus radiata died from Diplodia pinea infection, and the timber rapidly turned blue (Laughton, 1937), This is a severe loss when one considers that one acre of Pinus radiata in Victoria has a potential value of �500 to �1,000.