Sudden decline of cabbage tree (Cordyline australis): Search for the cause

Many cabbage trees (Cordyline australis) are dying throughout much of the North Island and the northern South Island of New Zealand. The symptomatology 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. This disease, which has been named Sudden Decline, usually leads to almost total defoliation of affected trees within 2-12 months. Disease incidence has increased linearly at about 11% per annum since 1987/88. Cultivated trees of C. kaspar; C. obtecta and various Cordyline hybrids have also been observed dying with Sudden Decline symptoms. Investigations ai:med at identifying the causal agent are described, and the hypothesis is advanced that a phytoplasma (mycoplasma-like organism or MLO) is the cause. Sudden Decline is contrasted with the widespread ill- health apparent in many pastoral populations of cabbage tree throughout the country. This Rural Decline is characterised by a general loss of branch and leaf vigour and occasional tree death. It is suggested that Rural Decline is a complex disease (decline disease) caused by various biotic and abiotic agents interacting with an ageing population growing in situations where regeneration is prevented. In many pastoral situations Sudden Decline is superimposed on Rural Decline. The ecological implications of Sudden Decline are discussed.