Black & Green Gram
Most of the damage to plant parts is inflicted during the larval stage. Larvae feed on the inner contents of the plant and on the seeds within the pods. Initial symptoms appear as boreholes on the floral buds, flowers and green pods soon after the larvae hatch. Damage on the pods is characterized by round holes and frass deposits at the entry point, usually close to the pod end. Honey dew secretions and movement of black ants around the secretion points can also be observed. Black discoloration indicates pod decay. Since the larvae directly attack the pods, the infestation leads to heavy yield loss.
The damage on plants is mainly caused by the larvae of Lampides boeticus. Adults are metallic to darkish blue and have a long bluish-gray body with blue hairs. Black spots are visible in the bottom of the hindwings, along with a elongated appendage. The underside is characterized by numerous irregular white and brown stripes and brown spots, usually near the edge of the wing. Females lay round pale blue or white eggs singly on floral buds, flowers, immature pods and on growing shoots and leaves. The larvae are pale green to brown, slightly round and look like slugs. The larval stage can last two to four weeks depending on the temperature.
The infestation can be controlled effectively through the release of natural enemies in the field. Egg and larvae parasitoids such as Trichogramma chilotraeae, Trichogrammatoidea bactrae, Cotesia specularis, Hyperencyrtus lucoenephila and Litrodromus crassipes may have a good effect. Biopesticides containing Paecilomyces lilacinus and Vetricillium lecani can be used as foliar application to control the infestation. Spray NSKE 5% twice followed by Neem oil @ 2% for the control of larvae.
Always consider an integrated approach with preventive measures and biological treatments if available. Chemical treatment may not be necessary if populations of natural enemies are preserved. If insecticides are needed, products containing lambda-cyhalothrin, deltamethrin can be sprayed and may give a level of control between 80 and 90 % in cowpea and mung bean. Other active ingredients include emamectin 5%SG (220 g/ha) and indoxacarb 15.8%SC (333 ml/ha). Keep in mind that the pea blue butterfly might develop resistance to these chemicals.