Rainfall increased the severity of leaf blight caused by Cylindrocladium quinqueseptatum [Calonectria quinqueseptata] on Eucalyptus tereticornis and the disease further intensified when an intercrop (taungya) of Manihot utilissima [M. esculenta] was cultivated in a 2-yr-old plantation in Kothamangalam Forest Division, Kerala, in 1982-83. Zingiber officinale had already been raised as a first year taungya crop in 1981-82. Severity of the disease was positively correlated with high rainfall pattern, while high relative humidity appeared to have little impact on disease severity.