Sudden Decline of Cabbage Tree (cordyline Australis): Search for the Cause

Since the late 1980s widespread death of cabbage trees (Cordyline australis) throughout much of the North Island has caused concern to the general public, managers and users of parks and reserves, and researchers concerned with indigenous biota. We have been studying the nature of these deaths, in an effort to understand the causes and thus underpin future management and control of the problem (Beever, 1990). A number of other researchers have studied particular aspects, and there has been widespread speculation as to the cause (Rudman and Nixon, 1992; Simpson, 1993a). In this paper we distinguish two syndromes: Sudden Decline, the death of apparently healthy trees over a period of months (Rees-George, Robertson and Hawthorne, 1990); and Rural Decline, the general loss of branch and leaf vigour and occasional death of trees that is occurring over much of the rural landscape often in the presence of grazing stock (Beever and Forster, 1992). We conclude that Sudden Decline is a biotic disease caused by an as yet unidentified agent, and Rural Decline is a complex disease caused by various biotic and abiotic agents interacting with an ageing population. In many lowland North Island areas Sudden Decline is superimposed on Rural Decline. Some Definitions