Cotton Diseases and Control

Introduction to Cotton diseases

            Cotton is one of the major commercial crops grown for its fiber. The scientific name of Cotton is Gossypium sp. There are a lot of cotton varieties cultivated across the world. The demand for Cotton farming is rapidly increasing. As the demand increases, the area under cotton cultivation is also increasing. In the present times of agriculture farming, there is a huge scope for cotton farming in the future decades. The ultimate goal is to increase the crop of the yield of cotton per acre. However, the maximum yield in cotton farming is achieved only if we take proper care and management from sowing to harvesting. Even though there are some cotton diseases caused by various plant pathogen that is leading to huge crop losses in farming. However, the losses caused by diseases in the cotton crop is minimized if we take prophylactic diseases controlling measures.

            Below are the details of the major plant pathogenic diseases of cotton, their symptoms and control as well as management practices.

Bacterial Diseases of Cotton

Bacterial blight or Angular leaf spot or Black arm

Causal organism: Xanthomonas campestris pv. Malvacearum   

Symptoms of Bacterial blight diseases of Cotton

The bacterium Xanthomonas campestris pv. Malvacearum  attacks all the stages from seed to harvest. The five common phases of the disease symptoms are given below.

  • Seedling blight: Small, water-soaked, circular or irregular lesions develop on the cotyledons. Later, the infection spreads to stem through petiole and cause withering and death of seedlings.
  • Angular leaf spot: Small, dark green, water soaked areas develop on lower surface of leaves, enlarge gradually and become angular when restricted by veins and veinlets and spots are visible on both the surface of leaves. As the lesions become older, they turn to reddish brown colour and infection spreads to veins and veinlets.
  • Vein blight or vein necrosis or black vein: The infection of veins causes blackening of the veins and veinlets, gives a typical ‘blighting’ appearance. On the lower surface of the leaf, bacterial oozes are formed as crusts or scales. The affected leaves become crinkled and twisted inward and show withering. The infection also spreads from veins to petiole and cause blighting leading to defoliation.
  • Black arm: On the stem and fruiting branches, dark brown to black lesions are formed, which may girdle the stem and branches to cause premature drooping off of the leaves, cracking of stem and gummosis, resulting in breaking of the stem which hang typically as dry black twig to give a characteristic “black arm” symptom.
  • Square rot / Boll rot: On the bolls, water soaked lesions appear and turn into dark black and sunken irregular spots. The infection slowly spreads to entire boll and shedding occurs. The infections on mature bolls lead to premature bursting of bolls. The bacterium spreads inside the boll and lint gets stained yellow because of bacterial ooze and looses its appearance and market value. The pathogen also infects the seed and causes reduction in size and viability of the seeds.

 How to control Cotton Bacterial blight disease

  • Remove and destroy the infected plant debris.
  • Rogue out the volunteer cotton plants and weed hosts.
  • Follow crop rotation with non-host crops.
  • Early thinning, good tillage, early irrigation, early earthing up and addition of potash to the soil reduces disease incidence.
  • Grow resistant varieties like HG-9, BJA 592, G-27, Sujatha, 1412 and CRH 71. Suvin is tolerant.
  • Gossypium herbaceum and G. arboreum are almost immune. G. barbadense, G. hirsutum, G. herbaceum var typicum and G. herbaceum var acerifolium have considerable resistance.
  • Delint the cotton seeds with concentrated sulphuric acid at 125ml/kg of seed.
  • Treat the delinted seeds with Carboxin at 2 g/kg seed or soak the seeds in 1000 ppm Streptomycin sulphate overnight or treat the seed with hot water at 52-560C for 10-15 minutes.
  • Spray with bactericides like Streptomycin sulphate (Agrimycin 100), 500 ppm along with Copper oxychloride at 0.3%.

Fungal Diseases of Cotton

Fusarium wilt disease of Cotton

Causal organism of Fusarium wilt disease: Fusarium oxysporum f.sp. vasinfectum

Symptoms of Fusarium wilt disease of Cotton

  • The disease affects the crop at all stages.
  • The earliest symptoms appear on the seedlings in the cotyledons which turn yellow and then brown.
  • The base of petiole shows brown ring, followed by wilting and drying of the seedlings.
  • In young and grown up plants, the first symptom is yellowing of edges of leaves and area around the veins, i.e. discolouration starts from the margin and spreads towards the midrib.
  • The leaves loose their turgidity, gradually turn brown, droop and finally drop off.
  • Symptoms start from the older leaves at the base, followed by younger ones towards the top, finally involving the branches and the whole plant. T
  • The defoliation or wilting may be complete leaving the stem alone standing in the field. Sometimes partial wilting occurs; where in only one portion of the plant is affected, the other remaining free. The taproot is usually stunted with less abundant laterals. Browning or blackening of vascular tissues is the other important symptom, black streaks or stripes may be seen extending upwards to the branches and downwards to lateral roots. In severe cases, discolouration may extend throughout the plant starting from roots extending to stem, leaves and even bolls. In transverse section, discoloured ring is seen in the woody tissues of stem. The plants affected later in the season are stunted with fewer bolls which are very small and open prematurely.

 How to control Fusarium wilt disease in Cotton

  • Treat the acid-delinted seeds with Carboxin or Chlorothalonil at 4 g/kg or Carbendazim@2g/kg seed.
  • Remove and burn the infected plant debris in the soil after deep summer ploughing.
  • Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers.
  • Multiply Trichoderma viride (2kg) in 50 kg of Farm yard manure for 15 days and then apply to the soil.
  • Apply heavy doses of farm yard manure or other organic manures at 10 t/ha. Follow mixed cropping with non-host plants to lower the soil temperature below 200C by providing shade.
  • Soil amendment with zinc.
  • Grow disease resistant varieties of G. hirsutum and G. barbadense like Varalakshmi, Vijaya, Pratap, Jayadhar, Jarila, Jyothi, G 22 and Verum.

Verticillium wilt disease of Cotton

Causal organism of Verticillium wilt disease of Cotton:  Verticillium dahliae

Symptoms of Verticillium wilt disease of Cotton

  • The symptoms are seen when the crop is in squares and bolls. Plants infected at early stages are severely stunted.
  • The first symptoms can be seen as distinct mottling of leaves with pale yellowish irregular areas at the margins and between the principal veins.
  • In addition, the yellowish areas become pale, more whitish and extensively necrotic.
  • Furthermore, necrosis of the leaves spreads from lower to upper leaves and there is heavy defoliation.
  • Finally, the affected leaves fall off leaving the branches barren. Infected stem and roots, when split open, show a pinkish to pinkish brown discolouration of the woody tissue which may be continuous or interrupted.
  • Pinkish streaks alternating with healthy tissue (Tiger stripe) are seen on removing the bark of the roots, stem and petiole. The affected plants may bear a few smaller bolls with immature lint.

How to control Verticillium wilt disease of Cotton

  • Treat the delinted seeds with Carboxin@4g/kg or Carbendazim at 2 g/kg.
  • Remove and destroy the infected plant debris after deep ploughing in summer months.
  • Apply heavy doses of farm yard manure or compost at 10t/ha.
  • Follow crop rotation by growing paddy or Lucerne or chrysanthemum for 2-3 years.
  • Spot drench with 0.05% Benomyl or Carbendazim.
  • Grow disease resistant varieties like Sujatha, Suvin and CBS 156.

Root rot disease of Cotton

Causal organism of Root rot disease of Cotton: Rhizoctonia bataticola

 Symptoms of Root rot disease of Cotton

  • The fungus causes three types of symptoms, viz., seedling disease, sore-shin and root rot.
  • Germinating seedlings of one to two weeks old are attacked by the fungus at the hypocotyl and cause black lesions, girdling of stem and death of the seedling, causing large gaps in the field. In sore-shin stage (4 to 6 weeks old plants), dark reddish-brown cankers are formed on the stems near the soil surface which later turns dark brown or black and plant breaks at the collar region leading to drying of the leaves and subsequently the entire plant.
  • Typical root rot symptom appears normally at the time of maturity of the plants. The most prominent symptom is sudden and complete wilting of plants in patches in concentric circles. Initially, all the leaves droop suddenly and die within a day or two.
  • The affected plants when pulled reveal the rotting of entire root system except tap root and few laterals.
  • The bark of the affected plant shreds and even extends above ground level. In badly affected plants the woody portions may become black and brittle.
  • A large number of dark brown sclerotia are seen on the wood or on the shredded bark.

How to control Root rot disease of Cotton

  • Treat the seeds with Trichoderma viride @ 4g/kg or Pseudomonas fluorescens @ 10g/kg of seed.
  • In addition, treat the seeds with Carboxin or Thiram at 4 g or Carbendazim at 2g/kg.
  • Spot drench with 0.1% Carbendazim or 0.05% Benomyl.
  • Also apply farm yard manure at 100 t/ha or neem cake at 2.5t/ha.
  • Adjust the sowing time, early sowing (First Week of April) or late sowing (Last week of June) so that crop escapes the high soil temperature conditions.
  • Adopt intercropping with sorghum or moth bean (Phaseolus aconitifolius) to lower the soil temperature.
  • Grow resistant varieties like KH 33/1146, 15/KW-2 (MB).

Grey or Areolate mildew disease of Cotton

Causal organism of Grey or Areolate mildew disease of Cotton: Ramularia areola (Sexual stage: Mycosphaerella areola)

 Symptoms of Grey or Areolate mildew disease of Cotton

  • The disease usually appears on the under surface of the lower leaves when the crop is nearing maturity.
  • Irregular to angular pale translucent lesions which measure 1-10 mm (usually 3-4 mm) develop on the lower surface, usually bound by veinlets.
  • On the upper surface, the lesions appear as light green or yellow green specks.
  • In addition, whitish grey or frosty powdery growth, consisting of conidiophores of the fungus, appears on the lower surface.
  • Furthermore, when several spots coalesce, the entire leaf surface is covered by white to grey powdery growth.
  • Finally, the infection spreads to upper leaves and entire plant may be affected. The affected leaves dry up from margin, turn yellowish brown and fall off prematurely.

How to control Grey or Areolate mildew disease of Cotton

  • Remove and burn the infected crop residues.
  • Rogue out the self-sown cotton plants during summer months.
  • Avoid excessive application of nitrogenous fertilizers/manures.
  • Adopt the correct spacing based on soil conditions and varieties.
  • Spray the crop with Carbendazim@0.1% or BM@1% or Wettable sulphur at 1.25-2.0 kg/ha, repeat after a week.
  • Grow the resistant varieties like Sujatha and Varalakshmi.

Anthracnose disease of Cotton

Causal organism of Anthracnose disease of Cotton: Colletotrichum capsici

Symptoms of Anthracnose disease of Cotton

  • The fungus infects the seedlings and produces small reddish circular spots on the cotyledons and primary leaves.
  • The lesions develop on the collar region, stem may be girdled, causing seedling to wilt and die. In mature plants, the fungus attacks the stem, leading to stem splitting and shredding of bark.
  • The most common symptom is boll spotting. Small water soaked, circular, reddish brown depressed spots appear on the bolls.
  • The lint is stained to yellow or brown, becomes a solid brittle mass of fiber. The infected bolls cease to grow and burst and dry up prematurely.

How to control Anthracnose disease of Cotton

  • Treat the delinted seeds with Carbendazim or Carboxin@2g/kg or Thiram or Captan at 4g/kg.
  • Remove and burn the infected plant debris and bolls in the soil.
  • Rogue out the reservoir weed hosts.
  • Spray any of the following fungicide combinations
    • Azoxystrobin 8.3%  + Mancozeb 66.7% WG @ 3 gm/lt water.
    •  Tebuconazole 50%+ Trifloxystrobin 25% WG @ 500 gm/ acre.
    • Metiram 55% + Pyraclostrobin 5% WG @ 1gm/lt water.
    • At boll formation stage with Mancozeb@0.25% or Copper oxychloride@0.3% or Ziram@0.25% or Carbendazim@0.1%.

Leaf spots disease of Cotton

  • Alternaria,
  • Cercospora,
  • Helminthosporium and Myrothecium

Alternaria leaf spot disease of Cotton

Causal organism of Alternaria leaf spot disease of Cotton:  Alternaria macrospora

Symptoms of Alternaria leaf spot disease of Cotton

  • The disease may occur in all stages but more severe when plants are 45-60 days old.
  • Small brown, round spots surrounded by a purple margin appear on leaves.
  • On older leaves the necrotic center of the spots may be marked by a pattern of concentric zonation.
  • In addition, several spots coalesce together to form blighted areas.
  • Under humid weather conditions the spots appear as sooty black leading to premature defoliation. Sometimes stem lesions are also seen.
  • Finally, in severe cases, the leaf stalk and bolls become infected with spherical or elliptical purple spots.

How to Control Choenophora Blight Diseases in Paddy

How to control Alternaria leaf spot disease of Cotton

  • Remove and destroy the infected plant residues.
  • Deep summer ploughing.
  • Avoid seeds from infected crop
  • Spray Mancozeb@0.25% or Copper oxychloride@0.3% at the initiation of the disease. Four to five sprays may be given at 15 days interval.
  • Spray Azoxystrobin 8.3%  + Mancozeb 66.7% WG  @ 3gm/lt water.
  • Spray Metiram 55% + Pyraclostrobin 5% WG @ 1ml/lt water.

Cercospora Leaf spot disease of Cotton

Causal organism of Cercospora Leaf spot disease of Cotton: Cercospora gossypina

Symptoms of Cercospora Leaf spot disease of Cotton

  • Usually the symptoms appear on lower leaves.
  • Firstly, small water soaked lesions appear on upper surface of leaf.
  • Later, spots enlarge and develop into circular or irregular spots with grayish white centre surrounded by brown margin.
  • Furthermore, many such spots coalesce to form big irregular patches.
  • Finally, the centre of the spot may fall off leading to shot hole formation. The leaves may drop off.

How to control Cercospora Leaf spot disease of Cotton

  • Remove and destroy the infected plant residues.
  • Spray  Mancozeb@0.25%    or        Copper           oxychloride@0.3%   or zineb@0.2%          or vitavax @1ml/lt water at the initiatial stage of the disease.
  • Spray Azoxystrobin 8.3%  + Mancozeb 66.7% WG  @ 3gm/lt water.

Helminthosporium Leaf spot disease of Cotton

Causal organism of Helminthosporium Leaf spot disease of Cotton: Helminthosporium gossypii

Symptoms of Helminthosporium Leaf spot disease of Cotton

  • The spots are greyish white in colour with deep purple margin on leaves.
  • Usually circular spots may coalesce leading to the drying of leaves.

How to control Helminthosporium Leaf spot disease of Cotton

  • Remove and destroy the infected plant residues.
  • Spray fungicide such as Mancozeb@0.25% or Copper oxychloride@0.3% or BM@1% at the initiation of the disease.
  • Spray Azoxystrobin 8.3% + Mancozeb 66.7% WG  @ 3gm/lt water.
  • Grow resistant varieties like SRT-1, AC 738, PS 10 and JR 78.

Rust disease of Cotton

Causal organism of Rust disease of Cotton: Phakopsora gossypii (Tropical rust), Puccinia cacabata (South western rust), Puccinia schedonnardi (Cotton rust-USA)

Symptoms of Rust disease of Cotton

  • Most common symptom of Cotton rust disease is the appearance of bright yellow orange spots usually on under surface of the lower leaves of the plant.
  • These bright yellow orange spots also known as pustules are surrounded by purple borders.
  • Spots become brown colour with age. Spots may appear on any of the above ground parts including bracts and bolls.
  • Severe infections may cause defoliation and reduction in the size of the cotton bolls.
  • Finally, on the stems and petioles, these pustules are usually elongated and are not much raised.

How to control Rust disease of Cotton

  • Spray fungicides such as Mancozeb@0.25% prior to first spore showers from gramma grass.
  • Spray Picoxystrobin 6.78% + Tricyclazole 20.33% W/WSC @ 400ml/acre.

Conclusion of Diseases of Cotton

            This is all about major and minor diseases of cotton, their symptoms, and management practices from the seedling stage to the harvesting stage. For more details regarding the diseases of Cotton, comment below.

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