A series of studies are reported, including a survey of nurseries and plantations in Kerala before and during the monsoons of 1979-83, in vitro conidial germination, infection of 4-month-old E. grandis seedlings by spraying with a conidial suspension of C. [Calonectria] quinqueseptatum and screening of 8 provenances of E. grandis and 7 provenances of E. tereticornis for susceptibility to a conidial spray of C. quinqueseptatum. Nine species (including Cylindrocladium clavatum, C. scoparium, C. ilicicola, C. parvum, C. floridanum, C. camelliae, C. curvatum and C. [Calonectria] theae) were found to be associated with Eucalyptus spp., causing a complex of damping off, stem canker, leaf and shoot blight in nurseries. In plantations, only leaf spot, leaf blight and shoot dieback were common. Leaf diseases usually began to appear on lower branches indicating infection from the soil. In areas of high humidity, infection could be severe, producing complete defoliation. In younger plantations, where tapioca was cultivated as a taungya crop, infection of leaves and branches was very severe, probably because of the damp microclimate caused by the tapioca. Infection was usually spread by conidia in rain or dew drops. Leaf infection was generally through the epidermis, occasionally through the stomata.