DISEASES OF CASTOR – Agricultural study materials

DISEASESCAUSAL ORGANISM
Seedling blightPhytophthora parasitica
RustMelampsora ricini
Leaf blightAlternaria ricini
Brown leaf spotCercospora ricinicola
Bacterial leaf blightXanthomonas campestris pv. ricini

1. SEDLING BLIGHT – Phytophthora parasitica

Symptoms

The disease appears as circular, dull green patch on both the surface of the cotyledonary leaves. Later it spreads and cause rotting. Infected stem show black discolouration and severe defoliation

Mode of spread and survival

The pathogen spreads through wind borne sporangia and survives in seeds and as oospores in soil

Epidemiology 

    Cool and moist conditions, continuous rains encourage the disease development.

Management

  • Diseased plants should be removed and burnt
  • Avoid low-lying and ill drained fields for sowing
  • Seed treatment with thiram @ 3 g/kg of seed



2. RUST – Melampsora ricini


Symptoms

Minute, orange-yellow coloured, raised pustules appear with powdery masses on the lower surface of the leaves. Pustules are grouped in concentric rings and drying of leaves results. The fungus produces only uredospores in caster plant

Mode of spread and survival

The pathogen spreads through air borne uredospores and survives in the self-sown caster crop

Epidemiology 

    Cloudy weather favour the disease

Management

  • Rogue out the self sown caster crop and other weed host
  • Sulphur dusting @ 25 kg/ha or spraying mancozeb @ 1 kg/ha


3. LEAF BLIGHT – Alternaria ricini

Symptoms

In leaves, irregular brown spots with concentric rings, variable in size appear which are usually surrounded by yellow halos. In severe cases, the stem, capsules, and inflorescence also show dark brown lesions and premature defoliation occurs.

Mode of spread 

Spreads through air borne conidia

Survival

The pathogen is externally and internally seed borne

Epidemiology 

High relative humidity, low temperature with moist condition favour the disease

Management 

  • Seed treatment with thiram or carbendazim @ 2 g/kg of seed
  • Three spray of mancozeb at 1 kg/ha at 15-90 days intervals


4. BROWN LEAF SPOT – Cercospora ricinicola

Symptoms

Minute brown spots surrounded by a pale yellow halo. Infected leaf tissue in the spot may break off leaving a shot hole symptom 

Mode of spread 

Spreads through air borne conidia

Survival

The pathogen survives as dormant mycelium in plant debris

Epidemiology 

Low temperature and cloudy weather encourage the disease

Management 

  • Remove the infected plant debris and destroy
  • Spraying with Bordeaux mixture @ 1 % or COC @ 0.25 %

5. BACTERIAL LEAF BLIGHT – Xanthomonas campestris pv. ricini

Symptoms

Water soaked lesions appear, which later become brown/black and angular to circular in shape. Later the affected leaves become brittle, dry up, drop prematurely and defoliate.

Mode of spread and survival

The pathogen spreads through rain splash and survives in the infested seeds

Epidemiology 

Poor drainage and heavy rain encourage the disease development

Management 

  • Use disease free seeds
  • Surface irrigation only during periods of low rainfall may serve to reduce losses.

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