Inoculum sources for coffee berry disease *

SUMMARY Isolates of Colletotrichum spp. from coffee berries and bark in Kenya fell into four categories, distinguishable by their cultural characteristics on agar. Three of these proved non‐pathogenic; the fourth invariably infected both wounded and unwounded berries and caused coffee berry disease. The sporulating capacity on bark of the various Colletotrichum strains showed peaks in the periods before both the long and the short rains. The pathogenic strain made up only a very small proportion of the whole Colletotrichum complex on the bark and its sporulating capacity never exceeded twenty spores/cm 2 /h. By contrast, a green berry with an active coffee berry disease lesion produced 5×10 4 conidia/h and an infected ripe berry twice as many. It is concluded that in any year, regardless of cropping pattern, diseased berries are likely to play an important role in the development of coffee berry disease.