SUDDEN DECLINE OF CABBAGE TREE (CORDYLINE AUSTRALIS) - SEARCH FOR THECAUSE

Many cabbage trees (Cordyline australis) are dying throughout much of the North Island and the northern South Island of New Zealand. The sym ptomatology of those dying in urban environments is described, and is concluded to be consistent with the hypothesis that death is caused by a biotic agent entering through a leafy tuft of the branch system. Th is disease, which has been named Sudden Decline, usually leads to almo st total defoliation of affected trees within 2-12 months. Disease inc idence has increased linearly at about 11% per annum since 1987/88. Cu ltivated trees of C. kaspar; C. obtecta, and various Cordyline hybrids have also been observed dying with Sudden Decline symptoms. Investiga tions ai:med at identifying the causal agent are described, and the hy pothesis is advanced that a phytoplasma (mycoplasma-like organism or M LO) is the cause. Sudden Decline is contrasted with the widespread ill -health apparent in many pastoral populations of cabbage tree througho ut the country. This Rural Decline is characterised by a general loss of branch and leaf vigour and occasional tree death. It is suggested t hat Rural Decline is a complex disease (decline disease) caused by var ious biotic and abiotic agents interacting with an ageing population g rowing in situations where regeneration is prevented. In many pastoral situations Sudden Decline is superimposed on Rural Decline. The ecolo gical implications of Sudden Decline are discussed.