Cercospora canescens (Cercospora leaf spot)

The symptoms of the disease are not particularly characteristic and are often similar to others caused by other species of Cercospora on the same crops. The leaf spots caused by C. canescens are subcircular to broadly irregular, sometimes confluent, generally brown, pale tan to grey centre surrounded by a dark brown or reddish margin. Characteristic lesions are round, brown and necrotic with dark, slightly depressed edges. C. canescens causes damage to fruits. The fungus grows radially on the surface of and inside the fruits, damaging them completely.

Spore suspensions sprayed on susceptible varieties of mungbean resulted in no differences in host response up to the flowering stage; but lesion severity increased sharply from this stage onward. Only 3 of 200 accessions were consistently resistant (Mew et al., 1975). The fungus has been studied in culture. The effects of cowpea leaf diffusates on conidial germination and germ tube growth were described by Schneider and Sinclair (1975). They found that both these processes were inhibited on the surfaces of young leaves but not on those of older leaves.

The disease is of relatively minor importance although it was described as a severe leaf spot of bambarra groundnut (Voandzeia subterranea) in Ghana.