Black & Green Gram
The primary symptom of the disease is a mild chlorotic mottle on young leaflets, which later develop into chlorotic and necrotic ring spots and streaks. The necrosis later extends to petioles, and upward the stems to terminal buds, resulting in the decay of floral structures, hence the name bud necrosis disease. This scenario is favored by moderately high temperatures. Infected plants show stunted growth, general chlorosis, proliferation of new shoots and deformation of new leaves. Pegs can be mottled and discolored and contain small, shriveled seeds with spots on them. Yield losses are observed when plants are infected at early stages.
Peanut bud necrosis disease is caused by a virus. The infestation of plants is persistent and depends on a species of insects (Thrips palmi) that feeds on plant tissues and sap. In the absence of peanut plants, the thrips feed on and infest alternative hosts in or around the field, for example southern marigold (Tagetes minuta), and subterranean clover (Trifoleum subterraneum). Hence, the removal of these plants is particularly important to control the insect population. Planting densely also discourages thrips from landing on the groundnut crop.
Spraying with plant extracts of sorghum or coconut leaf 20 days after sowing is effective in controlling thrips populations.
Always consider a integrated approach with preventive measures and possible biological treatments. Chemical treatment of viral infections is not possible. However, some treatments are available for the control of the thrips vectors. Spraying insecticides like dimethoate or thiamethoxam 30-35 days after sowing as a preventive measure can significantly reduce the incidence of bud necrosis. Seed treatment with imidacloprid @ 2ml/kg seed is also effective against thrips.