Abstract: The role of weeds, soil and plant debris in the epidemiology of foliar diseases of yam was investigated at Ibadan Western Nigeria in the lowland humid tropics. Sclerotium rolfsii, Colletotrichum gloeosporioides, Colletotrichum graminicola, Pestalotia sp., Curvularia lunata, Curvularia eragrostidis, Drechslera sp. and Rhizoctonia solani, fungi that can be pathogenic on yam (Dioscorea alata) were isolated from weeds in the vicinity of the yam plots. Plant debris found with the yam plots also contained Sclerotium rolfsii, Colletotrichum gloeosporioides and Rhizoctonia solani. High inoculum densities of 4.61±0.36x105 cfu g-1 of S. rolfsii, 3.22±0.14x105 cfu g-1 of R. solani and 4.32±0.39x105 cfu g-1 of C. gloeosporioides were recorded in soil obtained from yam fields that were manually weeded 3 times during the experimental period. Soil samples in yam plots that were manually weeded 3 times and those yam plots prepared by clearing and burning the debris in situ, had varying inoculum densities of these pathogens. On yam fields with burnt debris, the incidence of Sclerotium leaf blight, Rhizoctonia leaf blight, Curvularia leaf spot and Pestalotia leaf spot were lower than those recorded after other treatments. In fields with burnt debris, the incidence of anthracnose from C. gloeosporioides was 26.9%, while in yam fields that were weed free and those that were manually weeded 3 times, the incidence of the anthracnose disease was 45.3 and 65.7%, respectively.