leaf spot  (Myrothecium roridum) 

Identification

Myrothecium leaf spot  appears in  severe  form causing even the defoliation. The first appears on the young plant leaves only (4 to 6 week), but later may cause pre-emergence and post-emergence damping-off of  seedlings. The leaf spots are initially circular with tan coloured with violet-brown margins. The diseased spots are often surrounded by translucent areas which are concentrically zoned bearing black pinhead sized sporodochia. In severe cases, the stem may also break. It does affect the bolls and boll lesions damage the lint by making them brittle and discoloured.

Management

• Crop residues should be removed and while preparing the fields, care must be taken to deeply  ploughing in order to bury and destroy the remaining  part of plant tissues. 

• Weeds which serve as the alternate host should be completely removed and destroyed by burning.

• Use acid-delinted seeds to avoid seedborne inoculum.

• Early sowing (in north India) reduces the disease incidence.

• Wider spacing reduces the build-up of humidity thus curtailing the disease intensity.

• On the first appearance of the disease in field, copper oxychloride @ 2-2.5% and carbendazim @ 0.1% must be sprayed to check and control the disease. However, the other fungicides reoprted to be effective are, captafol, maneb, zineb, thiram, blitox-50 and delsan.