Spotted Stem Borer in Sorghum

The moth is medium sized and straw colored.

The Female lays nearly 500 eggs in masses of 10 to 80 on the undersurface of leaf, often near the midrib. The eggs are flattish and oval and tend to overlap like fish scales

The eggs hatch in 4 to 5 days and the larva attacks sorghum plants. The larval period lasts from 19 to 27 days and during this period the sorghum crop is damaged.

It infests the crop from second week till maturity.

Crop damage

The first indication that a sorghum plant is infested by the stem borer is the appearance of small elongated holes in young whorl leaves

Then the plant may become very ragged in appearance as the severity of attack increases.Subsequently larvae bore into the stem and shot-holes appear.

The larvae tunnels into the stem and eat the central portion.Consequent to eating the central stem portion, the growing point is killed and deadheart symptoms appear in whorl leaves.

Subsequently, the larvae bore into the stem resulting in extensive tunneling. The larvae also attacks earheads. Tunneling of earheads results either in its breakage , or complete or partial chaffy earheads affecting grain development.

Management

The stem borer survives during the off-season through the stubbles left in the field after harvest as well as in the stems kept for use as fodder. So, uprooting and burning of the stubbles and chopping of stems prevents its carry over to the next season. Select and grow varieties resistant to spotted stem borer.

A large number of predators attack this pest. Chemical control is required only when the infestation is very severe. The use of chemical sprays should be carried out after assessing the infestation levels from leaf damage symptoms. Need-based application at 20 and 35 days after crop emergence will be effective with either Carbofuran 3G or Carbaryl 4G at 8 and 12 kg/ha respectively.