The Sudden-Death Disease of Cloves and Its Economic and Agricultural Significance

Abstract

I. As the result of epidemiological evidence on the rate of spread of the Sudden-death disease of cloves in Pemba, the situation was thought sufficiently serious to justify an attempt to control the disease in advance of scientific proof of its aetiology. Although this attempt was eventually abandoned, many data were collected in preparation for it. This article reviews the history of the abortive control scheme, and discusses the data acquired. 2. From the results of a partial survey made in 1948 and another in 1949-50, there is an estimated total of over 2,000 separate outbreaks of disease in Pemba. These vary in size but average 25 dead trees. New outbreaks are constantly arising and the present annual rate of increase in number of outbreaks would seem to be about 14 per cent. Outbreaks increase in size at a highly variable rate but, on the average, the radial rate of spread is approximately constant. An attempt has been made to forecast the probable future development of the disease. 3. The effects of the disease on the economy of the Protectorate is discussed, and on the assumption that direct control is a practical impossibility suggestions are made for rehabilitation in Zanzibar Island, where up to the present the disease has caused much greater destruction than in Pemba. These are based on elimination of residual sources of disease in already devastated areas, followed by planned replanting with cloves and with other crops in order to achieve diversity.