Cotton

Crisis Management

Climatic Factors Other Factors Reddening Bud And Boll Shedding Drought Condition Growth Regulators Nutritional Imbalance

Other factors include

• Competition between vegetative and reproductive growth.
• Inadequate moisture absorption by plants and excessive transpiration due to high temperature and hot winds cause high shedding.
• Low ‘N’ supply during peak flowering encourages poor setting and heavy shedding.
• Injuries caused by insects cause shedding.

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Leaf Reddening

Introduction

• Leaf reddening is a special physiological disorder of cotton – not found in any other cultivated crop.
• Leaf reddening is often confused to symptoms of Magnesium deficiency or jassid attack. But, in Mg. Deficiency only the older leaves are affected and symptoms are seen from leaf margin. Further, Mg. Deficiency induces purplish red colour. Even in case of jassid attack, the leaves lost turgidity and leaves turn yellowish and later slightly reddish with a typical cup shaped turning of margins.
• But, in leaf reddening disorder, a normal young and old leaves suddenly turn to red without any symptoms of margin distortion. The attack starts from midrib rather than margin.
• It is more prevalent in hybrid cotton in Karnataka.

Reasons :

Number of reasons are ascribed to leaf reddening – which is essentially loss of chlorophyll in parasite tissue upsetting chlorophyll:

Anthocyamin balance

It is a disorder caused by shortage of supply of nitrogen and phosphorous or due to the failure in their translocation to leaves.

Such situation may arise due to any of the following reasons :

• Poor soils – with less capacity to supply N&P
• Repeated cultivation of cotton on same land without required manurial applications to build up organic C.
• Application of inadequate fertilizers.
• Droppage of night temperatures – which reduces the translocation
• Severe shortage in soil moisture – also reduce the translocation.
• Cultivation of hybrid cotton in sandy soils with poor water holding capacity and poor fertility.

Remedies :

• Assess the damage and if damage is more than 10-15% of the total crop, remedial measures can be taken up.
• Usual remedy for red leaf disorder include spraying 2% DAP or 2% urea at an interval of 8-10 days till the symptoms subside.
• If reddening is due to drought conditions, mulching may provide some relief.
• In irrigated conditions, soil application of DAP may help in reducing the leaf reddening @ 50 Kg./ha.

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Bud and boll shedding

Droppage Of Squares, Flowers, Bolls

Reasons

The droppage of squares, flowers and bolls is natural and inherent in cotton as a response to imbalance between sink (flowers, bolls and squares) to source (leaves) relation.

Besides genetic reasons, all the cotton varieties and hybrids will invariably drop their flowers, squares and buds due to –

• Reduced number of leaves, when insects attack them and force them to drop.
• Squares, flowers and bolls themselves are attacked by insects.
• Nutritional inadequacy – when the crop is not able to get adequate nutrients, either due to poor soil fertility or due to unbalanced/insufficient application of fertilizers.
• Climatic changes like prolonged cloudy weather, rains during peak flowering, sudden droppage in night temperature, prolonged drought.
• Any one of the above may be able to promote the droppage and reduce the yields.

Management

• Identification of reason for droppage is very important, as management differs for different reasons.
• Farmers can ignore natural droppage due to genetic characters without accelerated by any specific pre-disposing reason. Farmer can do nothing to manage such droppage.
• If the droppage is due to insects, all the dropped squares, flowers and bolls show some kind of attack. If such droppage is of higher order – immediate spray of suitable insecticide will reduce the droppage.
• If the droppage is due to leaf fall – identifying the reasons for leaf fall is necessary. Usually leaves do not fall unless they grow to maturity. In cotton, the normal age of leaf is not more than 60-80 days. Hence, when crop is beyond 60 days, the older leaves may naturally fall and process continues.
• If the leaf fall is due to insects and such leaves are abnormal or not fully-grown – then use of insecticides to reduce the sucking pests will not only reduce the leaf droppage but ultimately reduce the droppage of squares, flowers and bolls.
• In case the droppage is due to nutritional inadequacy, usually spray of 2% Urea or 2% DAP can take care of droppage temporarily. It will have to be supported by soil application of N-fertilizers.
• In dry land conditions, if the crop experiences N shortage and the soil is dry then 2% Urea or 2% DAP sprays will have to be continued once in 8-10 days till boll maturation is completed.
• Climatic changes like cloudy weather, rains during flowering, drop in night temperature promoting the droppage can not be tackled at all. One has to wait for improvement of weather foregoing the losses caused by them.
• In case of drought promoting the droppage, farmer can irrigate the land or he may provide mulch to reduce the evaporation from soil.
• Spraying NAA - 20 ppm may help in retaining the squares, flowers and bolls – which would have dropped as a variety character.

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Drought condition

Cotton crop can tolerate drought to some extent but not the water logged condition.

• Drought at early season is proved to be beneficial, but severe drought at early stages reduces the vegetative growth and finally the yield.
• Drought at reproductive stage results in square and boll drop

Remidies

• Thin out the population and maintain optimum plant stand.
• Opening of furrows which acts as conservation structure for moisture.
• Cultivation of drought resistant varieties.
• Conserve soil moisture by mulching.
• Use of anti transparent.
• By giving life saving irrigation.

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Growth regulating substances

• Like IAA, NA, GA plays important role in shedding of reproductive organs shedding mainly depends on auxins level in leaf petiole and stem. Cotton boll is not shed till auxin flow from the subtending leaf to the developing bolls or both maintained gradient across the pedicle to the branch.
• GA enhances fruit setting by stimulating growth and vigour of young plant. ABA enhances ethylene production which leads to the formation of abscission zone at higher concentration.
• GA/NA is applied through external source and gradient is maintained to prevent shedding.
• GA (planofix) which sprayed externally decreases the shedding of flowers and increases the number of flowers.

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Nutritional imbalance

• Developing bolls needs regular supply of Carbohydrates(CHO) and other nutrient which decides the fruiting potential of the crop.
• Shedding of bolls is also "cut out phenomenon" of the plant because of increased number of bolls and buds, plant retains certain number of bolls to maintain balance between vegetative growth and reproductive growth.
• Application of N results in more number of bolls/plant but percent of shedding was not affected.

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