Physiological disorders and leaf reddening problems of cotton
Harjeet Singh Brar and Paramjit Singh
PAU, Regional Research Station, Bathinda
Cotton is predominately cultivated in south western districts of the Punjab namely Bathinda, Mansa, Fazilka, Muktsar, Faridkot, Sangrur and Barnala. In addition to different factors like insect pest, diseases and weeds, physiological disorders and nutrient deficiencies/imbalances are also responsible for yield losses in cotton. Mostly the physiological disorders are taken lightly, but might cause huge yield loss in cotton. While, Parawilt and Tirak are physiological disorder having no association of any pathogen, but leaf reddening due to mostly nutrient deficiencies. Hence, knowing the causes, symptoms, extent of incidence and its management is a matter of serious concern for realizing the full yield potential of this crop.
Parawilt: Parawilt is a physiological disorder and is not caused by any pathogen. it was first reported in southern part of India in the year 1978.
Symptoms: Wilting occurs on scatted plants by sudden drooping of leaves in a sporadic manner. Prolonged drought conditions, bright sunlight, high temperature followed by heavy irrigation/ rainfall create environment for parawilt. Excess water create anaerobic condition resulted in high ethylene production in plant causes sudden wilting of plants and after 48 hours there sets a permanent wilting. Unlike pathogenic wilt, root systems of the affected plants remain intact and there is no rotting symptom on roots or browning of vascular bundle.
Timely diagnosis and treatment is most important to save crop from parawilt. Parawilting can be managed by foliar application of cobalt chloride (ethylene production inhibitor) @ 10 mg per litre of water (10 ppm) at initial stage of wilting. Plants will not recover after permanent wilting. Treatment is effectively only at initial stage of wilting. The affected plants will recover within a week of spray. The precautionary spray before irrigation/rainfall is not effective for parawilt.
Preparation of stock solution of cobalt chloride: The stock solution should be prepared by dissolving 2 grams of cobalt chloride in one litre of water. Then 75 ml of this solution should be dissolved in 15 litres of water and sprayed on the parawilt affected plants only.
Leaf reddening: It is most common problem of high yielding cotton hybrids sown on light soils.
Symptoms: High yielding cotton hybrids shows reddening of leaves at peak flower and fruit development stage. This is because of lack of sufficient quantity of nutrient in light soils to feed the crop plants having huge number of flower and boll retention. However, most of nutrients are applied through soil application of fertilizers and deficiencies of micronutrient especially magnesium deficiency in plants despite its sufficient quantity in soil is also reason for this problem.
Management: If cotton field showed symptoms of leaf reddening during previous year, then 2 sprays of magnesium sulphate @ 1 per cent (1 kg magnesium sulphate dissolved in 100 litres of water) at full bloom and boll development stage must be given at 15 days interval before appearance of red leaves on crop. Spray of 1% magnesium sulphate not only manage leaf reddening but also improve yield of crop. Secondly, timely and balanced use of recommended dose of fertilizers is also helpful to prevent leaf reddening in cotton.
Bad opening of bolls (Tirak) is also non-pathogenic physiological disorder particularly in dry belt of Rajasthan and Haryana and adjoining of Abohar areas of Punjab. Tirak is very common in hybrids, which start early boll formation at very high temperature in June.
Symptoms: Symptoms of Tirak are the yellowing and reddening of leaves followed by bad opening of bolls. Tirak appears where cotton suffers from persistent drought with high temperature, nutrient deficiency on light sandy soils, inadequate irrigation and too early sowing or lack of plant protection measures. These factors may operate singly or in different combinations. Spell of high temperature during flowering and fruiting stages aggravate the intensity of this malady. The seed cotton yield, fibre and seed quality affected much by occurrence of severe form of tirk.
Management: Judicious use of fertilizers and timely irrigation during flowering and fruiting stages and use of recommended plant protection schedule help to reduce the intensity of this physiological disorder. In addition to this, crop sown after heavy pre sowing irrigation and delayed first irrigation to possible extent lead to better root penetration and it improves ability of crop plant to withstand in drought stress.