High incidence of pathogen blight in cotton crop in Punjab

Ludhiana, June 23: Leaf spots on cotton due to different fungal and bacterial pathogens have been noticed in Punjab with the cultivation of Bt cotton.

According to Punjab Agricultural University (PAU) plant pathologists Dr H S Rewal and Dr Chander Mohan high incidence of pathogen-alternaria blight was reported in many fields in Bathinda, Mansa and Faridkot districts last year.

Because of the attack of different fungal and bacterial pathogens cotton leaves develop pale green leaf spots with irregular margins. These spots enlarge, turn brown and are recognised easily due to the presence of concentric zones.

According to the pathologists severe infection causes shedding of leaves specially where soil is light in texture. The disease is more serious on plants having low vigour or those which are raised in fields having low potash.

According to the scientists another type of leaf spot is also gaining prominence in the region. The pathogen attacks both leaves as well as bolls. Circular to semi-circular brown coloured spots with broad violet margins appear on leaves, bracts as well as bolls.

Later on, small dark dot like structures are formed inside these spots.

The agri scientists said that fungus is seed borne and also survives on dead leaves. The disease is favoured by high humidity and rains. Dense growth in Bt cotton is favourable for the development of this pathogens.

As per the scientists, bacterial leaf blight, also known as angular leaf spot, is characterised by black arm and boll rot depending upon the portion of the plant affected. The disease appears on leaves in the form of minute, water soaked, angular spots which later on turn brown and it extends upto veins and veinlets which also turn black.

Spot on bolls appear as round water soaked areas which later turn dark brown or black and are slightly depressed. Spotted bolls may fail to open and lint may be discoloured with a yellow stain, they added.

Seed treatment before sowing is the best remedy against the leaf spot, the two scientists said. However, the infection at later stage can be controlled by spraying with Blitox and Streptocycline.

The sprays should be started just after the rains and depending upon the frequency of rains, two to three sprays should be given, the scientists added.

Meanwhile according to Dr N S Malhi, PAU's Director of Extension Education, farmers should use only recommended dose of DAP fertiliser in cotton crop. He said the plant clinic at PAU had witnessed some farmers coming with dying plants of cotton. The stem skin of such plants was rotten and had turned black in colour.

Explaining the reasons for this problem in cotton, Dr Malhi said that misuse of DAP in the fields had caused the cotton crop to die.

If the concentration of phosphorous in the soil was medium and recommended dose of phosphatic fertiliser was used for wheat in that soil, then there was no need to apply DAP or superphosphate for cotton in the same field.

However, in case of deficiency of phosphorous in soil, 27 kg of DAP can be used while sowing, he suggested.

He informed that phosphorous was such a nutrient that gets accumulated in top soil and cannot percolate deeper in the fields.

He advised the farmers against the use of non-scientific practices which harm the crop.

UNI