Lesson 2: Spotted Stem Borer

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Lesson 2 Spotted Stem Borer
The moth is medium sized and straw colored (Fig.).
Stem Borer moth and pupa
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 (Fig.).
Masses of eggs of Stem Borer
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Lesson 2 Spotted Stem Borer
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.
Stem borer larvae
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Lesson 2 Spotted Stem Borer
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 (Left Fig.).
Windows due to stem borer attack.
Then the plant may become very ragged in
appearance as the severity of attack increases
(Right Fig.).
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Lesson 2 Spotted Stem Borer
Crop damage Subsequently larvae bore into the
stem and shot-holes appear (Top Fig.). The
larvae tunnels into the stem and eat the central
portion (bottom Fig.)
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Lesson 2 Spotted Stem Borer
Crop damage Consequent to eating the central
stem portion, the growing point is killed and
deadheart symptoms appear in whorl leaves (bottom
Fig.)
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Lesson 2 Spotted Stem Borer
Subsequently, the larvae bore into the stem
resulting in extensive tunneling. The larvae
also attacks earheads. Tunneling of earheads
results either in its breakage (Fig.), or
complete or partial chaffy earheads affecting
grain development.
Breakage of earheads due to stem borer attack.
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Lesson 2 Spotted Stem Borer
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.
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Lesson 2 Spotted Stem Borer
Management Select and grow varieties resistant
to spotted stem borer.
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Lesson 2 Spotted Stem Borer
Management 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.