Grey mildew disease management in cotton

Grey mildew is an important fungal disease, which has been affecting cotton yield in India.

The disease increased by 10-30 per cent this year when compared to the prevalence in last four years.

It has become a major disease and needs effective control during early days only. Low temperature and humidity prevailing during the winter season also contribute to the disease intensity.

Symptoms

Initial infection appears as triangular, square or irregularly circular whitish spots of 3 to 4 mm size on leaves.

As the disease severity increases, the smaller spots merge together and form bigger spots.

The disease usually first appears on the lower canopy of older leaves when bolls set.

Profuse sporulation gives them a white mildew like appearance.

Irregular or angular translucent spots (areola) are formed by the veins of leaves. Disease severity is more spread in upper leaves, flowers and bolls.

Leaves become yellow, turn to brown colour. Severe intensity of grey mildew disease leads to leaf curling and eventually the defoliation of green leaves and both surfaces of the leaves get uniformly covered by white powdery growth of the fungus.

High humidity, low temperature help in the spread of this disease.

This pathogen survives mainly on plant debris and volunteer plants.

Control measures

— First foliar spray of 3 gm wettable sulphur per one litre of water in the initial stages of the disease to be done.

— Dusting of 8-10 kg of Sulphur powder effectively controls the disease.

— Also about one gram of Carbendazim or Benomyl per litre of water is effective.

— If the disease intensity is more, new fungicides like one litre Hexaconazole or 300 gm Nativo-75 WG per hectare is required to control the grey mildew disease.

— Deep ploughing, rotation crops like cereals, growing regional tolerant varieties, are recommended.

— Crop residues should be removed and burnt.

(Dr.A Vijaya Bhaskar Rao is Scientist (Plant Pathology), e-mail:av-bhaskar12@yahoo.co.in;Cell no:098498 17896 ,Regional Agricultural Research Station, Warangal, Jayasankar is professor, Telengana State Agricultural University (PJTSAU),Rajendranagar, Hyderabad.)