THE EFFECT OF COFFEE LEAF RUST ON FOLIATION AND YIELD OF COFFEE IN PAPUA-NEW-GUINEA

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.