The most important disease of clove trees in Zanzibar and Pemba is sudden-death disease. It has been known in Zanzibar for over a century and the periodical waves of incidence have culminated in losses which, since 1930, are said to have accounted for the destruction of about half the mature trees of Zanzibar Island and very numerous small outbreaks in Pemba.

Various die-backs have been described, including the sudden-death fungus, Valsa eugeniae, when entering the branches as a wound parasite. An extremely serious condition, however, is caused by the fungus Cryptosporella eugeniae Nutman & Roberts (syn. Endothia eugeniae (Nutman & Roberts) Reid & Booth). This is always associated with some form of injury to the tree, particularly when branches are broken during harvesting. The branch slowly dies back, the leaves turning brown, and the fungus proceeds downwards.

Finch (1973) considers a nutritional disorder as a possible cause and found that the leaves had a high level of manganese and aluminium and low levels of phosphorus and potassium. Waller and Sitepu (1975) suspect a pathological origin, but so far the organism responsible has not been discovered. The following fungi have been isolated, but none have been identified as the cause of Sumatra disease: Botryodiplodia theobromae Pat.; Botryosphaeria ribis Grossen. & Dugg.; Macrophoma eucalyptorum Tarconi – none of which are regarded as important pathogens – Fusarium oxysporum Schlect.; F. moniliforme Sheld.; F. dememcellulare Brick.; Cylindrocladium destructans (Zinssm.) Scholten; Rhizoctonia state of Thanatephorus cucumeris (Frank) Donk. and Macrophomina phaseoli (Matibl.)’ Ashby. The sudden death of Zanzibar, Valsa eugeniae Nutman & Roberts, has been found on one site and on an isolated tree elsewhere, but is unlikely to be the causal organism of Sumatra disease.

The whole process takes only a few clays. Examination in the earliest stages will show that the fine ramification of the root system has completely disappeared, and death is the direct result of water stress. The cambial areas of the collars of the trees are stained bright yellow, which later spreads up the trunk, and, after some months, the yellow stain becomes widespread throughout the tree.

Mutibudjang disease of cloves has been recognized in various parts of Indonesia for many years. The disease begins with a general decay of the fine feeder roots, which soon produces secondary leaf shedding and die-back, initially at the top of the crown and subsequently extending through the whole canopy. It produces a slow decline of the tree leading to complete death in two or three years from the onset of the symptoms.

Signs of debility may appear in such young trees when they are about eight years old and the symptoms of sudden death then follow, but spread out over many months or even years, the period of crisis occurring about the time that the young trees bear their first crop. It has been suggested that the slow decline of young trees may be at least postponed by keeping the plants in a vigorous vegetative condition by the use of shade, windbreaks, mulches, manuring, and even watering.