White Grub on Peanut
Both adults and larvae are damaging stage. The larvae feed on roots and damage pods. Grubs feed on fine rootlets and nodules. Affected plants are yellowish and wilted and die in patches. In annuals, sudden wilting is the earliest symptom. Plants that are attacked by adult beetles defoliate.
The adults are dark brown and about 20mm long and 8mm wide. Within three to four days after the onset of rain, they emerge from the soil, fly short distances and feed on the surrounding plants. After feeding, they reenter the soil to hide and lay their eggs. Female lays 20-80 white and roundish eggs singly at a depth of 5-8cm in the soil. The larvae are whitish yellow, translucent and about 5mm long.The fully grown grubs are stout with strong mandibles. Their head is yellowish and the white colored body is fleshy and 'C' shaped. They feed on organic matter for a few weeks and then feed on fine rootlets and pods. Besides groundnut, white grubs also feed on the roots of sugarcane, chillies, sorghum, maize, red gram or pearl millet.
Spray a liquid suspension of beneficial nematodes (Heterorhabditis sp. Mountain Tai 1) at 1.5 billion nematodes per hectare against grub larvae onto the soil in early season Use Solanum surattense extract as seed treatment. Treat the kernels with kerosene (one litre per 75 kg/seeds) before sowing. Conserve braconids, dragon flies, trichogrammatids. Bio-insecticides based on NPV and green muscardine fungus can also work.
Always consider an integrated approach with preventive measures together with biological treatment if available. On emergence from the soil, adults feed on foliage of certain nearby plants. Spraying these plants in the night with a persistent insecticide such as carbaryl or endosulfan reduces the population of adults before egg laying.