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Introduction
The
disease appears first on
the lower canopy of older leaves
when the plant attains maturity, usually after first boll set. It
appears in the form of irregular angular, pale translucent spots 1-10 mm in
diameter with a definite or irregular margin formed by the veins of leaves
(called ‘areolae’).
Symptoms
The dorsal surface of the leaves show profuse
sporulation (giving the lesions a white mildew-like appearance) causing light
green to yellowgreen coloration on the ventral (upper)
leaf surface which in due
course becomes necrotic
and dark brown in color at
this stage, they can be easily mistaken from the angular leaf spot phase of
bacterial blight. The severely affected leaves often defoliate and results in
premature boll opening with immature lint.
Management
-
Crop
residues should be removed and the fields must be deeply ploughed in order
to bury and destroy the remaining plant tissues.
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Crop
should be rotated with cereals, and preference should be given to tolerant
varieties such as Sujata, Suvin, ERB 4492 and SB 289 E(barbadense),
Laxmi and Sangam (hirsutum) and Varalaxmi (intraspecific) in
disease endemic areas.
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Foliar
application of sulphur dust/wettable sulphur @ 10 kg/ha or 2-3 gm/l
at 10 days interval from the day of first appearance, or sulphex 80 WP
(0.25%) or benomyl, carben
dazim @ of 200‑300 gm a.i. /ha is effective in controlling the
disease significantly.
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