Abstract

Cow pea (Vigna unguiculata L. Walp.) is one of the economically significant legume crops of India growing in an area of 0.5 million ha. The legume crop is also an important crop of Assam. In Assam 23 per cent of total cultivated area is legume and among this cow pea occupies a major area. The crop is highly prone to a wide range of pests and diseases, which can cause damage to the crop at all the growth stages. Amongst different viral diseases cow pea mosaic disease transmitted by Aphis craccivora Koch is one of the important disease, causing a yield loss of 40-60 per cent. In this study an effort was made to prevent the secondary spread of the disease by controlling its vector. The effort was to develop bioformulation of entomopathogenic fungi to manage the disease for sustainable growth of the crop. For that, efficacy of the liquid bioformulation and suspension concentrate of Metarhizium anisopliae was tested against cow pea aphid, Aphis craccivora in pot as well as field condition. Liquid formulation of M. anisopliae supplemented with Glycerol (10.0%) + Sunflower oil (0.5%) was found to significantly effective protecting leaf infestation up to 88.11 per cent and shoot infestation up to 95.65 per cent. Highest aphid mortality (80%) was recorded at 30 days after spraying with protection of secondary spread of cow pea mosaic disease up to 100 per cent and 96.03 per cent in pot and field condition respectively. Protection of cow pea mosaic disease by spraying liquid formulation of M. anisopliae amended with Glycerol (10.0%) + Sunflower oil (0.5%) at 15 days interval for twice proved to be the best treatment with highest yield of 24.03 q/ha and a cost benefit ratio of 1:7.95 as compared to control (11.20 q/ha). Study on the morphological changes of A. craccivora due to the infection of M. anisopliae with the help of Scanning Electron Microscope (SEM) revealed that ventral cuticle and abdomen of aphid have totally distorted with deformation of all the body parts resulting in its death.