Anthracnose of Blackgram
The infection can occur at any growth stage and is visible on leaves, stems, petioles and pods. If the infection occurs after seed germination or if the seeds are infected, seedlings will show minute rust specks that slowly enlarge to form eye-spots and finally get blighted. On older plants, initial symptoms appear as small and irregular dark brown to black water-soaked spots, more commonly on the lower surface of leaves or petioles. Over time, the spots grow into sunken lesions with darker centers and yellow, orange or bright red margins, and also appear on the upper surface of leaves. Pods have rust-colored lesions and might shrivel and dry up. In case of heavy infection, affected parts might wilt and wither off. The development of cankers on stems and petioles is usually followed by defoliation.
The fungus Colletotrichum lindemuthianum survives in the soil and on infected seeds and plant debris. It also overwinters in alternative hosts. The spores are transferred to the growing seedlings via rain, dew or field work when foliage is wet. It is thus important to restrict the activity in the field (workers, treatments...etc) when the foliage is wet from rain or dew. Cool to moderate temperatures (13-21°C) and periods of frequent rainfall are also favorable to the fungus and its transmission, resulting in increased occurrence and severity of the infection.
Biological agents might help to control the infection. The fungus Trichoderma harzianum and the bacteria Pseudomonas fluorescens used as a seed treatment compete with Colletotrichum lindemuthianum.
Always consider an integrated approach with preventive measures together with biological treatments if available. Chemical treatment of the disease may be economically inviable depending on the given weather conditions. Seeds can be treated with carbendazim at 2 g/kg. If fungicides are needed, spray products containing folpet, carbendazim or mancozeb when the foliage is dry.