Calonectria rigidiusculahas been found associated with an acute and a chronic form of dieback of cacao. It can also infect cankers caused primarily byPhytophthora palmivora, and the lesions following attack by the capsidsSahlbergella singidarisandDistantiella theobroma.The association with the capsid lesions is of great economic importance since it appears that capsids alone are capable of killing only green shoots, and that the severe damage caused to woody shoots followsC. rigidiusculainfection of the capsid lesions. Acute dieback occurs only in certain districts after exceptional drought and may be considered primarily the result of environmental conditions. The main importance of chronic dieback is that it prevents the recovery of cacao which has been seriously weakened from other causes.C. rigidiusculainfection retards the healing ofP. palmivoracankers and also produces a lesion in the xylem tissue which may be extensive.C. rigidiusculahas been established in wounded cacao stems of all ages without difficulty. The spread of the fungus is slow, but is more rapid in the xylem than in the cortical tissues. Spread is greatest in the unlignified tissues.