Disease Management

Introduction Diseases at Different Crop Stages Detailed Study of Diseases Frog eye leaf spot/Cercospora leaf spot Bacterial leaf spot (Xanthomonas Vesicatoria) Damping off (Pythium aphanidermatum) Anthracnose / Die back and Fruit rot (Colletotrichum capsici) Powderymildew (Leveillula taurica) Fusarium wilt (Fusarium oxysporum f.sp.capsici) Viral diseases Mosaic Viruses


  • Plant Diseases are caused by Bacteria, Fungi, Virus and Other sources.
  • Disease can affect the yields through reduction of photosynthetic area in early stages and infestation on reproductive parts and economic produce at later stages.
  • Disease causes reduction on photosynthate flow in the plant (equivalent to blocking of pipes).

Disease Symptoms

  • A disease symptom in a plant is expressed in the form of a distinct localized structural change on the host tissue.
  • The changes are Cytological, Histological & Morphological in nature.
  • The following symptoms are important for our discussion.


  • Change in color of whole plant or parts and the intensity of Discoloration depends on intensity of disease. Ex:- Yellowing, browning, blackening, silvering and Chlorosis.
  • These symptoms are usually more in shoots, buds, and fruits, less in stem and roots.

Spots and short holes

  • Spots vary in size and color and margin of spots also vary in pattern and color.
  • Margins may be circular and irregular spots may be isolated and coalesce after development.
  • Spots generally occur in leaves but sometimes also on due to death and drying of tissue and finally fall off resulting in a shot hole. ·


  • Sometimes it misleads to toxic effects of foliar sprays of pesticides resulting death of tissue.

Factors Influencing Disease Symptoms

Host parasite relation: The intensity of the disease depends upon the susceptibility / Resistance of the host to the pathogen.

Environmental factors: can be grouped as Soil borne seed borne and Air borne

Soil borne: Soil pH, Structure, Texture Moisture, Organic matter, fertility, cultural operations, Irrigation.

Seed Borne: Seed Moisture, Storage environment

Air Borne: Temperature, RH, and Rainfall Wind.


Diseases at Different Crop Stages

Stage important
Factors favouring infection

Damping off

Seedling (nursery)

  • Seedlings killed before emergence
  • Water soaking and shrivelling of stem

Moist soils poordrainage 90-100% R.H soil temperature 20°C

Anthracnose /Dye back /Fruit rot

  •  Circular spots, water soaked sunken with black margins on fruits
  • Fruits with may spots drop off prematurely

Infected seed airborne wind – blown rains

Frog eye leaf spot


  • Brown and circular leaf lesions with light grey centres
  • Dark brown margins
  • Elliptical lesions on stem, petiole and peduncle

  • Prolonged period of wetness
  • Seed and infected crop residues

Powdery mildew

Any stage of growth in main field

  • Disease progresses from the older to younger leaves
  • Shedding of foliage

  • Warm climate both dry and humid
  • More leaf shedding at low humidity
Fusarium wilt Nursery & mainfield
  •  Wilting of plant
  • Upward and inward rolling of leaves

  • High temperatures
  • Wet soil conditions

Bacterial leaf spot

Main field all stages of crop

  • Leaves, stems and fruits are affected

  • young leaves – spots are yellowish green
  • On older leaves– dark water soaked spots
Cloudy weather

Leaf curl

Main field all stage of crop

  • Leaves curl towards midrib and become deformed
  • Flower buds absice before attaining full size
  • Anthers do not contain pollen grains
Virus generally transmitted by white-fly

Mosaic Viruses

Mainfield at all stages of crop

  • Light and dark green patches on leaves

  • Yellowing and chlorotic ring spots on leaves and fruits

Virus transmitted by insect vectors.

(Sucking pest)


Detailed Study of Diseases

Frog eye leaf spot / Cercospora leaf spot (Cercospora capsici)

Seasonal occurrence

  • Both in nursery and mainfield may be affected by this disease.


  • Extensive defoliation occurs under prolonged periods of wetness.
  • Fungus can survive on seed and infected crop residues.

Nature and symptoms of damage

  • Leaf lesions typically are brown and circular with small to large light grey centres and dark brown margins. The lesions may enlarge to 1cm or more in diameter and some times coalesce.
  • Stem, petiole and pod lesions also have light grey centres with dark borders, but they are typically elliptical.
  • Severely infected leaves drop off prematurely resulting in reduced yield.

Control measures

  • Spray twice at 10-15 days interval with 2.5g Mancozeb or 1g Carbendazim/lit of water.


Bacterial leaf spot (Xanthomonas Vesicatoria)

Seasonal Occurrence

  • Disease seen in post rainy season viz., October to December.

Nature and Symptoms of Damage

  • Leaves, stems and fruits are affected.
  • On young leaves the spots are yellowish green, on older leaves they are dark and water soaked. Lesions on leaf begin as circular, water soaked spots may develop straw coloured centres and dark margins.
  • Severely spotted leaves turn yellow and drop., defoliation is common.
  • On the fruits, small blister - like spots occur becoming warty in appearance later.
  • Narrow, elongated leisions or streaks may develop on stems.

Control measures

  • The bacteria is seed - borne and the seeds can be treated with corrosive sublimate. It is also soil-borne and hence crop rotation is essential.
  • The nurseries and plants in the mainfield may be sprayed with a copper fungicide such as Bordeaux mixture.
  • Spray 2 or 3gms of Plantomycin or Paushamycin mixed with 30gms of Copper Oxychloride (blitax or phytolon) per 10 litre of water twice or thrice at 15 days interval depending on the severity of the disease.


Damping off (Pythium aphanidermatum)

Seasonal occurrence

  • Damping off is very common disease in nurseries.


  • Disease is most damaging on moist soils with poor drainage.
  • Fungus is mainly soil - borne. It requires humidity in the range of 90-100 percent and a soil temperature nearer 20oC.
  • When there is sufficient moisture in the soil, it germinates and produce mycelium which later forms the asexual stage of reproduction. The fungus is capable of living for many years in soil.

Nature & symptoms of damage

  • Seed may rot or the seedlings may be killed before they emerge from the soil. Stem of young seedlings may also be attacked after emergence showing water soaking and shrivelling of stem which fall over and die.
  • In nursery the disease may appear in patches in 2-4 days, the entire lot of seedling may be destroyed.

Control measures

  • Partial sterilization of soil by burning trash in the surface helps in checking the disease.
  • Follow cultural practices such as thin planting (600 - 750g seed per cent) on raised seedbeds.
  • Use of light textured soils provides better drainage and aeration.
  • Use of well decomposed manure.
  • Soil sterilization by drenching the soil 4" deep with Formaldehyde diluted 50 times with water or with some other effective chemical soil sterilant.
  • Soil drenching with 1% Bordeaux mixture or 3g Copper Oxychloride like Blue copper per litre of water at 12 and 20 days after sowing is also useful.
  • Seed treatment with 3g Captan or Thiram per kg seed
  • Seed treatment with 4g Trichoderma viride formulation combined with 6g Metalaxyl is highly effective.


Anthracnose / Die back and Fruit rot (Colletotrichum capsici)

Seasonal occurrence

  • One of the worst diseases of chilli found in India and it occurs in severe form in all southern states.


  • Fungus is externally seed-borne and the secondary spread is through air-borne inoculum. The disease spreads rapidly with wind blown rains during rainy season. Fungus may not survive long in the soil but may survive on the dead twigs stored under dry conditions.

Nature and symptoms of damage

Disease symptoms appear mostly on ripened fruits and hence the disease is also called as ripe fruit rot.

  • The spots are usually circular, water-soaked and sunken with black margins. The sunken spots covered with a pinkish mass of fungal spores. As the disease advances the spots spread, forming concentric markings with dark fructifications representing the fungal acervuli.
  • The fruits with many spots drop off prematurely resulting in heavy loss of yield.
  • Fungus may also attack the fruit stalk and spread along the stem causing dieback symptoms.

Control Measures:

  • Use disease free seed. Seed - borne infection is controlled by seed treatment with 3g Captan or Mancozeb per kg seed.
  • The secondary spread causing fruit infections may be checked by spraying the plants with copper fungicides at fortnightly interval beginning from the time, the first bunch of fruits is almost mature.
  • Spraying with Captafol at 0.2% followed by Copper Oxychloride at 0.25% and Carbendazim at 0.1%.
  • On screening the cultivars for resistance to this disease, the cultivar pant C-1 recorded only less than 5% incidence of anthracnose and fruit rot and there by exhibited some degree of resistance.


Powderymildew (Leveillula taurica)

Seasonal occurrence

  • This disease very common from December to February


  • Disease occurs in warm climates both dry and humid.
  • Leaf shedding is more pronounced at low humidity.

Nature and symptoms of damage

  • Chlorotic blotches or spots appear on the upper leaf surface.
  • When lesions are numerous they may coalesce resulting in a general chlorosis of the leaves.
  • On the lower leaf surface, the lesions are covered with a white to gray powdery growth.
  • The disease progresses from the older to younger leaves and shedding of foliage is prominent symptom.

Control measures

  • Spray thrice at 10-15 days interval with 1ml Dinocap or 2g Wettable Sulphur per litre of water.
  • Before flowering, dusting 8-10 kg Sulphur per acre is also useful.


Fusarium wilt (Fusarium oxysporum f.sp.capsici)

Disease Cycle

  • Fungus causing this disease can live for several years in the soil.


  • High temperatures and wet soil conditions favour disease development. Disease is most likely occur in poorly drained soils. Hence, provision of drainage is necessary to control this disease to some extent.

Nature and Symptoms of damage

  •  Fusarium wilt is characterised by wilting of the plant and upward and inward rolling of the leaves. The leaves turn yellow and die.
  • Generally appear localised areas of the field where a high percentage of the plants wilt and die, although scattered wilted plants may also occur.

  • Disease symptoms are characterised by an initial slight yellowing of the foliage and wilting of the upper leaves that progress in a few days into a permanent wilt with the leaves still attached.
  • By the time above - ground symptoms are evident, the vascular system of the plant is discoloured, particularly in the lower stem and roots.

Control measures

  • Use of wilt resistant varieties.
  • Drenching with 1% Bordeaux mixture or Blue copper or Fytolan may give protection. Seed treatment with 4g Trichoderma viride formulation or 2g Carbendazim per kg seed is effective. Mix 2kg T.viride formulation mixed with 50kg FYM, sprinkle water and cover with a thin polythene sheet. When mycelia growth is visible on the heap after 15 days, apply the mixture in rows of chilli in an area of one acre.


Viral diseases

  • Among 18 naturally occurred viruses and 16 artificially transmitted viruses only the leaf curl virus and chilli mosaic virus were reported in India.
  • Among the viral diseases leaf curl is most serious.

Leaf curl

  • Leaves curl towards midrib and become deformed.
  • Stunted plant growth due to shortened internodes and leaves greatly reduced in size.
  • Flower buds abcise before attaining full size and anthers do not contain pollen grains.

  • The virus is generally transmitted by whitefly.
  • So control measures of whitefly in this regard would be helpful.


Mosaic Viruses

  • Light green and dark green patches on the leaves.
  • Stunted plant growth during early stages.
  • Yellowing, chlorotic ring spots on leaves and fruits.

Cucumber Mosaic Viruses

Tobacco Mosaic Virus

Tomato spotted wilt virus at different stages of crop growth

Mild mottle virus

Potato viruses

Management of viral diseases

  • Control measures are not known for majority of viral diseases.
  • Hence, mechanical, cultural methods are mostly recommended.
  • The infected plants should be uprooted and burnt or buried to avoid further infection.
  • Avoid monoculture of chilli crop.
  • Selection of healthy and disease - free seed.
  • Suitable insecticidal sprays reduce the incidence of viral diseases, since majority of viral diseases are transmitted by insect vectors.
  • Soaking seeds in a solution containing 150 g Trisodium orthriphosphate per litre of water for 30 minutes inhibits seed - borne inoculum.
  • Treated seed should be washed with fresh water and dried before sowing.
  • Nursery beds should be covered with nylon net or straw to protect the seedlings from viral infection.
  • Raise 2-3 rows of maize or sorghum as border crop to restrict the spread of aphid vectors.
  • Apply Carbofuran 3G @ 4-5 Kg/acre in the mainfield to control sucking complex and insect vectors selectively.
  • If it is not possible spray the crop with systemic insecticides like Monocrotophos 1.5 ml or Dimethoate 2ml of Acephate 1g per litre of water.
  • Collect and destroy infected virus plants as soon as they are noticed.


Andhra Pradesh