Cotton Disease Management: The Key To Higher Yields And Bigger Profits

Cotton (Gossypium sp) is one of the most important fibre and cash crop in India. It is vulnerable to infections by pathogens like fungi, bacteria and viruses. All parts of the plants are infected and crop losses are common in the crop. Cotton diseases can significantly reduce crop yield and cotton quality leading to reduced profits for farmers.  

The severity of yield loss depends on the type of disease, the timing of infection, and the environmental conditions. The estimated average yield loss due to cotton diseases in India ranges from 10% to 15%. However, in severe outbreaks, yield losses can be as high as 50% or more. Effective disease management can help minimize crop losses and improve yield. 

The Major Diseases of Cotton having significant impact on cotton yield are as follows;

1. Fusarium wilt:

Scientific name of causal agent: Fusarium oxysporum f.sp. vasinfectum 

Stage of occurrence: Affects at all stages of the crop 

Symptoms of Fusarium wilt in cotton: 

• Initially the symptoms appear as yellowing and browning of cotyledons and the base of petiole shows brown ring 
• It is followed by wilting and drying of the affected seedlings 
• Affected plant’s leaves loses turgidity, gradually turns brown, droops and finally drops off 
• Tap roots are usually stunted with a smaller number of lateral roots. 

• Vascular tissues show browning or blackening symptom and black streaks or stripes may extend upwards to the branches and downwards to the roots 
• Affected plants become stunted with fewer bolls which are very small and opens before attaining maturity 

Favourable conditions for Fusarium wilt infection in cotton: 

Soil temperature of about 20 – 30°C, warm and dry weather followed by rain, high dosage of nitrogen and phosphatic fertilizers, black soils with high alkaline reactions, and wounds caused by nematode and grubs of ash weevil are favourable conditions for fusarium wilt infestation in cotton. 

2. Verticillium wilt

   

Scientific name of causal agent: Verticillium dahliae 

Stage of occurrence: Square and boll formation stage 

Symptoms of Verticillium wilt in cotton: 

• Early infection leads to stunted growth of the plant 
• ‘Bronzing of veins’ followed by yellowing of leaves and interveinal chlorosis 

• It is followed by yellowing of leaves and interveinal chlorosis 
• Affected leaves dry up giving scorched appearance 
• Drying of leaf margins and areas between the leaves gives “Tiger stripe” or “Tiger claw” appearance 
• Branches remain barren due to falling of affected leaves 
• When infected stems and roots are split open, pinkish appearance of woody tissue can be seen 

• Affected plants may produce smaller bolls with immature lint 

Favourable conditions for Verticillium wilt infection in cotton: 

High nitrogen fertilization, heavy soil with alkaline reaction, low soil temperature (15-20°C), excessive soil moisture or poor drainage in soils, lack of crop rotation and presence of host crops like tomato, brinjal, chilli, bhendi can create favourable conditions for verticillium wilt infection. 

Management of Fusarium wilt and Verticillium wilt disease in cotton: 

3. Root rot:

   

Scientific name of causal agent: Rhizoctonia bataticola 

Stage of occurrence: Seedling to vegetative stage 

Symptoms of root rot in cotton: 

3 types of symptoms caused by the pathogen – Seedling disease, sore shin and root rot   

Seedling stage:  

• Germinated seedling affected by the fungus shows black lesions on hypocotyl 
• Causes girdling of stem and death of affected seedling 

Sore shin stage: 

• Dark reddish-brown canker appears on stem near soil surface, later turning black 
• Drying of leaves and entire plant due to plant breakage at the collar region 

Root rot: 

• Bark of affected plant shreds and may extend above ground level 
• Dark brown sclerotia appears on the wood or on the shredded bark 
• Entire root system becomes rotted, plants dry and can be easily pulled out 

Favourable conditions for root rot infection in cotton: 

Heavy rainfall followed by dry weather, high soil temperature of about 35 – 39°C, presence of host crop like vegetables, growing cotton after cultivation of oilseeds and legumes, wound caused by nematodes and ash weevil grubs increases root rot disease incidence. 

Management of root rot disease in cotton: 

4. Grey / Areolate mildew:

Scientific name of causal agent: Ramularia areola  

Stage of occurrence: Seedling to Reproductive stage  

Symptoms of Grey or Areolate mildew in cotton: 

• Irregular to angular pale translucent lesions appear on the lower surface of affected leaf 
• Light green or yellow green specks appear on the upper leaf surface 
• Whitish grey powdery growth appears on the lower surface, later coalesce and cover the entire leaf surface 
• Under severe infection, white/grey powdery growth may occur on the upper leaf surface 
• Affected chilli leaves dry up from margin, curl inward, turn yellow and fall off prematurely. 

Favourable conditions for Grey / Areolate mildew infection in cotton: 

Wet humid conditions, Low temperature (20 – 30°C), close planting, very early or very late sowing of cotton, intermittent rains and excessive application of nitrogenous fertilizers may increase grey mildew infection in cotton field. 

Management of Grey mildew in cotton: 

5. Anthracnose:

   

Scientific name of causal agent: Colletotrichum gossypii 

Stage of occurrence: All growth stages 

Symptoms of Anthracnose in cotton: 

• This disease affects all parts of the cotton plant 
• Small reddish circular spots appear on the cotyledon and primary leaves of seedlings 
• Causes seedlings to wilt and dry 
• In affected mature plants, stem splitting and shredding of bark can be seen 
• “Boll spotting” is the most cotton symptom 
• Sunken, circular, reddish-brown spots appear on the bolls and the infected boll stops to grow, burst and dry up.  

Favourable conditions for Anthracnose infection in cotton: 

Prolonged rainfall during the boll formation stage, presence of crop debris, weed hosts and close planting may be favourable for anthracnose infection in cotton. 

Management of Anthracnose in cotton: 

6. Alternaria leaf blight:

Scientific name of causal agent: Alternaria macrospora 

Stage of occurrence: Vegetative and Reproductive stage 

Symptoms of Alternaria leaf blight in cotton: 

• Small, brown, irregular or round spots appear on the leaves 
• Central lesion of each spot may be surrounded by concentric rings 
• These spots coalesce together, and form blighted areas 
• Affected cotton leaves become brittle and fall 
• In case of severe infection, spots may appear on bracts and bolls. 

Favourable conditions for Alternaria leaf blight infection in cotton: 

High humidity, temperature of about 25 – 28°C, intermittent rainfall, wet foliage, dense planting and presence of crop residues due to lack of field sanitation create favourable conditions for Alternaria leaf blight infection in cotton. 

Management of Alternaria leaf blight in cotton: 

Method of Application of Chemicals – Spraying 

7. Bacterial blight: 

Scientific name of causal agent: Xanthomonas campestris pv.malvacearum 

Stage of occurrence: Seedling to harvest 

Symptoms of Bacterial blight in cotton: 5 common phases of symptoms are noticed. 

• Seedling blight: Water soaked, irregular or circular lesions appear on the cotyledons, which may spread to petiole and stem causing withering and death of seedlings 
• Angular leaf spot: Small, dark green, water-soaked lesions develop on the under surface of leaves and become angular when restricted by veinlets and veins. Later, the lesions turn to reddish brown colour and becomes visible on both sides of the leaf 
• Vein blight/Vein necrosis/Black vein: Blackening of veins and veinlets gives ‘blighting appearance’. The presence of bacterial oozes on the lower side of the leaf. Affected leaves show crinkling appearance, withering and are twisted inward. 
• Black arm: Black lesions are developed on stem and branches, causing premature drooping of leaves, cracking of stem and gummosis, leading to die back 
• Boll rot: Dark black, sunken and irregular spots appear on the bolls. It leads to premature bursting of bolls. The spread of bacterium inside the bolls causes yellow staining of lint. 

Favourable conditions for Bacterial blight infection in cotton: 

Optimum soil temperature of 28°C, relative humidity of 85%, early sowing, high atmospheric temperature of 30 – 40°C, delayed thinning, late irrigation, poor tillage, K-deficiency in soil and rains followed by bright sunshine are highly favourable parameters for bacterial blight infection. 

Management of Bacterial blight in cotton: 

8. Para wilt or Sudden wilt:

• Exact cause of this physiological disorder is still unknown 

Stage of occurrence: Flowering and fruit filling stage 

Symptoms of Para wilt or Sudden wilt disease in cotton: 

• Premature death of top leaves, followed by collapse of the plant 
• Within few hours of heavy rainfall or soil saturation, wilting of leaves can be seen 
• If sunshine is brighter and hot, leaves may immediately dry 
• Wilted plants shed all the leaves and are left only with small immature fruits 
• Under cloudy weather, leaves turn yellow and die with no or little wilting 

Favourable conditions for Para wilt infection in cotton: 

Excessive water or sudden rainfall, poor soil drainage, bright sunshine or hot air temperature may create conditions favourable for para wilt incidence 

Management of Para wilt or Sudden wilt in cotton:  

The exact cause of this disorder is still unknown. Preventive measures can be taken to minimize the para wilt incidence to some extent. Some of the measures include growing wilt tolerant varieties, accurate management of irrigation, reducing waterlogging conditions by providing adequate drainage and maintaining optimum vegetative growth by avoid using excessive of FYM and fertilizers. 

9. Leaf curl disease

Scientific name of causal agent: Cotton leaf curl virus 

Stage of occurrence: All stages 

Vector: Whitefly 

Symptoms of leaf curl disease in cotton: 

• ‘Upward and downward curling’ of leaves and thickening of veins 
• Enation can be noticed on the underside of the leaves 
• In severe cases, all the leaves curl and the plant growth is retarded 
• Leads to reduced boll bearing capacity 

Favourable conditions for Leaf curl virus infection in cotton: 

Primary source of spread is Whitefly (Bemisia tabaci). Presence of alternate hosts like chilli, bhendi, tomato, warm temperature, late planting can be favourable for leaf curl virus infection.  

Management of Leaf curl virus in cotton: 

Spread of leaf curl virus disease can be managed by controlling the vector whitefly, which spreads the virus. The following chemicals can be used to control whitefly in cotton. 

10. Tobacco streak virus

    

Scientific name of causal agent: Tobacco streak virus 

Stage of occurrence: All stages 

Vector: Thrips (Thrips tabaci) 

Symptoms of Tobacco streak virus in cotton: 

• Ring like purplish necrotic spots appear on the leaves 
• Chlorotic streaks develop on the leaves 
• Stunted growth  

Favourable conditions for Tobacco streak virus infection in cotton: 

Presence of weed hosts, high temperature (25 – 30°C), infected plant debris may create favourable conditions for tobacco streak virus disease spread in cotton crop. 

Management of Tobacco streak virus in cotton: 

Spread of Tobacco streak virus disease can be managed by controlling thrips, which spread the virus. The following chemicals can be used to control thrips in cotton. 

(Note: Refer to the product label to find the right time of Application and more details of the product)