Himachal Mtghare

India is the largest producer of groundnut in the world. But average yields are low at 745 kg/ha. One of the important factor contributing to low yield is disease attack. Groundnut crop is prone to attack by numerous diseases to a much larger extent than many other crops. More than 55 pathogens including viruses have been reported to affect groundnut. Some diseases are widely distributed and cause economic crop losses while others are restricted in distribution and are not considered to be economically important at present. Among those disease some important diseases with their nature, symptoms and controls are described here :-


1- Early leaf spot

Causal Organism :-Cercospora arachidicola

Nature :- Soil and Air-borne

Favourable condition :-

Monoculture of groundnut.
lower temp (25o C).
long periods of high relative humidity and rainfall.

Symptoms :-

  1. Infection starts about 1 month after sowing.Small chlorotic spots appear on leaflets, with time they enlarge, turn brown to black and assume sub circular shape on upper leaf surface
  2. On lower surface of leaves light brown colouration is seen.
  3. Lesions also appear on petioles, stems, stipules.
  4. In severe cases several lesions coalesce and result in premature senescence.

Possible yield loss :- 10-50%

Control :-

  • Spray carbendazim 0.1% or mancozeb 0.2% or chlorothalonil 0.2%.
  • Foliar application of aqueous neem leaf extract (2-5%) at 2 weeks interval 3 times starting from 4 weeks after planting.

2- Late leaf spot

Causal Organism :- Phaeoisariopsis personatum

Nature :- Soil and Air-borne

Favourable condition :-

Temperature of 18-30o C.
magnesium deficiency.
heavy application of nitrogen and phosphorus fertilizers.

Symptoms :-

  1. Infection starts around 55-57 DAS in Kharif and 42-46 DAS in Rabi.
  2. Black & nearly circular spots appear on the lower surface of the leaflets.
  3. Lesions are rough in appearance. In extreme cases many lesions coalesce resulting in premature senescence and shedding of the leaflets.

Possible yield loss :- 10-50%

Control :-

  • Spray carbendazim 0.1% or mancozeb 0.2% or chlorothalonil 0.2%.
  • Foliar application of aqueous neem leaf extract (2-5%) at 2 weeks interval 3 times starting from 4 weeks after planting.

3- Rust

Causal Organism :- Puccinia arachidis

Nature :- Air-borne

Favourable condition :- Wet weather coupled with a temp of 22-25o C.

Symptoms :-

  1. Rust can be readily recognized as orange coloured pustules that appear on the lower leaflet surface and rupture to expose masses of reddish brown urediniospores.
  2. Pustules appear first on the lower surface and in highly susceptible cultivars the original pustules may be surrounded by colonies of secondary pustules.
  3. Pustules may also appear on the upper surface of the leaflet.
  4. The pustules are usually circular and range from 0.5 to 1.4 mm in diameter.
  5. They may be formed on all aerial plant parts apart from flower and pegs.
  6. Severely infected leaves turn necrotic and desiccate but are attached to the plant.

Control :-

  • Spray chlorothaalonil 0.2%; or mancozeb 0.25% or Hexaconazole/propaconazole to reduce disease incidence
  • Foliar application of aqueous neem leaf extract @ 2-5% is useful and economical for the control of rust.

4- Stem rot

Causal Organism :- Sclerotium rolfsii  

Nature :- Seed and Soil born

Favourable condition :- Severe with alternate wet and dry periods.

Symptoms :-

  1. The first symptom is the sudden wilting of a branch which is completely or partially in contact with the soil.
  2. The leaves turn brown and wilt but remain attached to the plant.Seeds in the infected pods show a characteristic bluish-grey discolouration
  3. At the junction of the branch with the stem near soil a white coating of fungus mycelium is formed.


Possible yield loss :- 27 % and more

Control :-

  • Seed treatment with 3 g thiram + Carbendazim.
  • Seed treatment with Trichoderma viride/T.harizanum @ 4 g/kg seed and soil application of Trichoderma viride/T.harizanum @25-62.5kg/ha, preferably in conjunction with organic amendments such as castor cake or neem cake or mustard cake @ 500 kg/ ha.

5- Alternaria leaf disease

Causal Organism :-  Alternaria arachidis and A. tenuissima

Symptoms :-

  1. Lesions produced by A. arachidis are brown in colour and irregular in shape surrounded by yellowish halos.
  2. Symptoms produced by A. tenuissima are characterized by blighting of apical portions of leaflets which turn light to dark brown colour.
  3. In the later stages of infection, blighted leaves curl inward and become brittle.
  4. The lesions become necrotic and brown and are round to irregular in shape.
  5. Veins and veinlets adjacent to the lesions become necrotic. Lesions increase in area and their central portions become pale, rapidly dry out, and disintegrate.
  6. Lesions can coalesce, give the leaf a ragged and blighted appearance.

Control :-

  • Foliar application of Mancozeb (0.3%) or copper oxychloride (0.3%) or Carbendazim(0.1%)

6- Anthracnose

Causal Organism :- Colletotrichum dematium and C. capsici  

Nature :- seed, soil and air-borne.

Symptoms :-

  1. Small water-soaked yellowish spots appear on the lower leaves which later turn into circular brown lesions with yellow margin 1 to 3 mm in diameter.
  2. In some cases lesions enlarge rapidly become irregular and cover the entire leaflet, and extend to the stipules and stems..

Control :-

  • Seed treatment with copper oxychloride or Mancozeb (0.3%) or Carbendazim (0.7%) are effective in controlling the anthracnose disease of groundnut.

Authrs:

Himachal Mtghare

Rashmi guraha

/ Dy.Directr f Agriculture, Raipur

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