Coffee leaf rust epidemics of varying severity were created by applica
tion of fungicide treatments, of varying concentration, to experimenta
l plots from 1989 to 1992. Detailed measurements of disease incidence
and leaf fall showed that yield and foliation (number of leaves per la
teral) in 1991 was affected by the disease incidence in the previous s
eason. Analysis showed a significantly greater influence of disease on
foliation, both within and between seasons, than on yield. This was c
onfirmed by data from 1992. It was concluded that the effect of the di
sease on yield is indirect through induction of defoliation.