DISEASES OF BLACK GRAM / GREEN GRAM, SOYBEANS, COW PEA

Agri Diseases

1. LEAF CURL – Tomato spotted wilt virus [TSWV]

Symptoms

The infection starts as chlorosis of lateral veins near the leaf margins and margins slowly curl downwards. The infected leaves are brittle and plants produce a few small and malformed pods.

Vector 

The disease is transmitted by Thrips viz., – Frankliniella schultzi, Thrips tabaci and Scirtothrips dorsalis

Epidemiology

Rainy days during kharif season favour high incidence of disease.

Management

  • Rogue out infected plants up to 30 DAS and remove the weed host.
  • Spray monocrotophos or methyl demeton @ 500 ml/ha on 30-45 DAS

DISEASES OF SOYBEAN

1. Downy mildew – Peronospora manshrica

Symptoms:

Downy mildew of soybean is characterized in its early stages by indefinite yellowish green areas on the upper surface of the leaves. As the disease progresses, those areas become grayish brown or dark brown and have yellowish green margins. Severely infected leaves fall prematurely. A grayish and mould like growth develop on the under of the lesions. 

Mode of spread and survival: 

    The spores produced on the mould growth on the leaves spread the disease from plant to plant. The fungus over seasons as oospores in infected leaves and on seeds. Secondary spread is through air borne sporangia formed on infected leaves.

Epidemiology:

    Downy mildew in favoured by high humidity and a temperature of 20-22°C.

Management: 

    Seeds from heavily infected fields should not be saved for planting. Seed treatment with fungicide improves emergence and may eliminate the occurrence of systemically infected seedlings. 

2. Soybean mosaic – Soybean mosaic virus or Soja virus I 

Symptoms:

    Plants infected early are stunted with shortened petioles and internodes. Leaves are small, misshaped, puckered and occasionally with dark green enations along the veins. Affected leaflets are generally asymmetric and curl downward at the margin. Seedlings from infected seeds are spindly with unifoliate leaves, curled longitudinally downward and rugose or crinkled. The leaves become pre maturely chlorotic and subsequent trifoliate leaves are more severely stunted, mottled and show rugosity. Diseased parts are small and flattened with less pubescence and are more acutely curved than pods on healthy plants.

Mode of transmission:

SMV – sap transmissible and aphids.

Management

  • Rogue out infected plants up to 30 DAS and remove the weed host.
  •  Spray monocrotophos or methyl demeton @500 ml/ha on 30-45 DAS.

DISEASES OF COW PEA

1. COWPEA APHID BORNE MOSAIC – Cow pea aphid borne mosaic virus

Symptoms

The disease affected plants are stunted and the leaves show variable amounts of dark green vein banding, leaf distortion and blistering. The infected plants produce few pods, which are small and distorted.

Transmission 

The disease is transmitted by insect vector aphid’s viz., Aphis craccivora, A. fabae, A. gossypii, and Myzus persicae. The virus is also seed borne and seed borne infection up to 3 per cent may be noticed. 

Management

  • Rogue out infected plant up to 30 DAS and remove the weed host.
  • Spray monocrotophos / methyl demeton @ 500 ml/ha to control the insect vectors.
  • Grow resistant varieties like CO 6.

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