Victoria’s wet mountain forests are the native habitat of the destructive spur legged phasmid, or stick insect, Didymuria violescens which can cause severe defoliation over large areas and often results in premature tree death.
From the late 1950s the Forests Commission had become concerned about a build-up of large populations of the stick insect.
The major infestations first appeared in summer 1960-61 and were most severe in the Upper Yarra Forest District near Powelltown, though stands in the Neerim, Erica, Marysville and Broadford districts were also infested. The potential loss of wood production because of premature tree death was significant.
The Forests Commission commenced aerial spraying with maldison in the Tarago and Tin Creek areas, south of Powelltown, in the summer of 1964-65.
The chemical had been successfully field-tested by the New South Wales Forestry Commission. Considerable research into the effect of spraying maldison on non-target insects showed that the overall impact was minor.
Spraying was undertaken between January and early February when the less destructive immature stages of the insect were present in the tree crowns.
Between 1968 and 1973, a major study of the biology of the native insect was carried out in even-aged stands of 1939 Eucalyptus regnans in the Central Highlands.
Survey results indicated that although aerial spraying prevented significant defoliation and crown dieback and tree death, the plague potential of subsequent generations had not been reduced. It was found that many stands required respraying in alternate years, and about twice the area of forest needed protection within four years of commencement of spraying.
Between 1964 and 1983, over 21,000 ha of high-quality ash forests in the Central Highlands and northeast Victoria in the Kiewa Valley was successfully treated by aerial spraying with maldison.
Ref: Fred Neumann, John Harris, Conrad Wood (1977) The phasmatid problem in mountain ash forests of the Central Highlands of Victoria, FCV Bulletin No. 25. https://drive.google.com/file/d/1q5SBbcZhmuWhWqrPYqKaX2rMmoakvTvx/view
Victoria’s Forests & Bushfire Heritage 