Bollworm in Sorghum
The moth is large and, brown or gray with specks that form a V-shaped mark on the fore wings. The hind wings are dull-colored, with a black border
The female moth lays spherical yellowish eggs in singles on the young sorghum heads.
The young larvae are whitish-green. Fully-grown larvae vary from almost black, brown or green to pale yellow or pink with light and dark stripes. Fully-grown larvae are about 40 mm long
The larval period lasts from 18 to 25 days when the sorghum heads are damaged.
Bollworms infest both whorls of leaves and earheads of sorghum. Infestation of earheads is more serious than infestation of whorls. Larvae that hatch from eggs feed on tender, folded leaves in the whorl, before earheads are available for them to infest. Damage to leaves usually does not affect yield. Infestation of sorghum earheads is of concern because Bollworm larvae feed on developing seeds. Small larvae at first feed on florets, then hollow out developing seeds. About 80% damage is caused by grownup larvae. Larval excrement or frass is common in infested heads and may be seen on the tops of upper leaves or on the ground under plants. Under certain conditions, seeds of infested earheads may develop mold fungus. Natural mortality, predators, parasites, pathogens, and cannibalism among larvae suppress abundance of Bollworms in sorghum whorls and panicles.
Tactic is to use cultivars with loose or open panicles. Larvae on open panicles are exposed to predaceous insects and birds.
Submitted by bharati on Thu, 24/09/2009 - 14:12