Bacterial pustule

The symptoms are much like those of bacterial blight. At first they appear as small, yellow-green spots with reddish-brown centres, more conspicuous on the upper surface of the leaf. A small, raised pustule usually develops at the centre of the lesion, especially on the lower leaf surface. This is the stage at which the disease is most readily distinguished from bacterial blight. The pustule and the absence of water soaking serve to distinguish bacterial pustule from bacterial blight. The latter shows water soaking at the centre or the margin of the dead area in the early stages of infection. In bacterial pustule, small infections may run together and cause large, irregular brown areas surrounded by a yellow margin. Parts of the brown dead areas may crack, giving the leaf a ragged appearance. The bacteria causing bacterial pustule over-season in diseased leaves and are seed-borne. Some strains infect common bean and cowpea.