A) DOWNY MILDEW OF PEA

Causal organism: Peronospora pisi
Sub-division: Mastigomycotina

Symptoms

• Early Infection: Causes systemic infection in young plants, leading to:
  • Sickly yellowish-green coloration.
  • Severe stunting and distortion.
  • Chlorosis (yellowing) of leaves.
• Secondary Infection: Localized in upper leaves, stems, tendrils, and pods:
  • Greenish-yellow to brown blotches on the upper leaf surface.
  • Downy, whitish fungal growth on the lower leaf surface.

Etiology

• Pathogen: Peronospora pisi is an obligate parasite.
• Mode of Reproduction: Asexual reproduction through sporangia and zoospores.
• Survival and Spread:
  • Overwinters in plant debris or infected seeds.
  • Spreads through windborne sporangia and zoospores in water.

Disease Cycle

• Primary Infection: Initiated by infected seeds or oospores present in the soil. Systemic infection occurs when seedlings grow from infected seeds.
• Secondary Infection: Occurs through zoospores released from sporangia on the lower leaf surface. Zoospores are spread by wind or splashing rain.

Favourable Conditions

• Cool temperatures (5 – 15°C).
• High humidity (over 90%) for 4 – 5 days.
• Early vegetative stage of seedlings is most susceptible.

Management

• Cultural Practices: Remove and destroy infected plants from the field. Ensure proper spacing for air circulation to reduce humidity.
• Seed Treatment: Metalaxyl @ 6 g/kg of seeds to prevent primary infection.
• Chemical Control: Foliar spray with Metalaxyl + Mancozeb (Ridomil Gold) @ 0.2%. Repeat sprays at 10-15 day intervals during favorable conditions.

POWDERY MILDEW OF PEA

Causal organism: Erysiphe polygoni
Sub-division: Ascomycotina

Symptoms

• White, powdery patches on both surfaces of leaves, tendrils, stems, and pods.
• As the disease progresses:
  • Patches coalesce, covering large areas and turning greyish-brown.
  • Infected parts become distorted and brittle, giving a dirty appearance.
  • Premature defoliation of leaves is common.

Etiology

• Pathogen: Erysiphe polygoni is an obligate parasite.
• Mode of Reproduction:
  • Asexual reproduction through conidia (spores).
  • Sexual reproduction through cleistothecia (overwintering structures containing ascospores).
• Survival and Spread:
  • Overwinters as cleistothecia on plant debris.
  • Conidia are spread by wind.

Disease Cycle

• Primary Infection: Occurs through ascospores released from cleistothecia in spring. Germination occurs on leaf surfaces under dry conditions.
• Secondary Infection: By conidia produced on infected leaves. Spread by wind to healthy plants.

Favourable Conditions

• Warm days and cool nights.
• Low humidity favors conidia germination.
• Dry weather promotes rapid disease spread.

Management

• Cultural Practices: Clean cultivation by removing and destroying infected plant debris. Crop rotation to break the disease cycle.
• Chemical Control:
  • Sulphur Compounds: Wettable sulphur @ 0.3%.
  • Systemic Fungicides: Karathane or Calixin @ 0.2%.
  • Timing of Sprays: At the first appearance of symptoms, repeat at 10-15 day intervals.

RUST OF PEA

Causal organism: Uromyces viciae-fabae
Sub-division: Basidiomycotina

Symptoms

• Initial Symptoms: Small, white, raised spots (pycnia) on the upper leaf surface. Yellowish-green flecks on the lower surface of leaves.
• Pustule Formation: Pustules (uredosori) appear on the lower leaf surface, turning reddish-brown. Uredospores released from pustules spread the disease to healthy plants.
• Advanced Symptoms: Pustules coalesce, leading to leaf yellowing and premature defoliation. Later, black telia (teliospores) appear, which help the fungus survive the offseason.
• Affected Parts: Leaves, stems, and pods.

Etiology

• Pathogen: Uromyces viciae-fabae is an obligate parasite.
• Spore Types:
  • Uredospores: Reddish-brown, round, and one-celled, causing secondary spread.
  • Teliospores: Two-celled, dark brown or black, responsible for overwintering.
• Survival and Spread: Survives in plant debris and on volunteer hosts as teliospores. Uredospores are wind-dispersed, leading to rapid spread in moist conditions.

Disease Cycle

• Primary Infection:
  • Initiated by teliospores germinating in the spring to produce basidiospores.
  • Basidiospores infect leaves, forming pycnia and then aecia, releasing aeciospores.
• Secondary Infection: Aeciospores infect pea plants, producing uredosori and spreading uredospores. Multiple cycles of uredospores occur in a single growing season.
• Overwintering: As teliospores on plant debris or in soil.

Favourable Conditions

• Moderate temperatures (15 – 25°C).
• High humidity and leaf wetness.
• Dense plant canopy, which increases humidity.
• Windy conditions help disperse uredospores.

Management

• Cultural Practices:
  • Remove and destroy infected plant debris after harvest.
  • Practice crop rotation with non-host crops.
  • Ensure proper plant spacing for good air circulation.
• Resistant Varieties: Use rust-resistant pea cultivars, if available.
• Chemical Control:
  • Protective Fungicides: Mancozeb @ 0.2% or Chlorothalonil.
  • Systemic Fungicides: Propiconazole or Hexaconazole @ 0.1%.
  • Spray Schedule: Start at the first appearance of symptoms and repeat every 10-15 days during favorable conditions.