CITRUS GUMMOSIS

Causal Organism:

• Phytophthora nicotianae var. parasitica, P. palmivora, P. citrophthora
• Sub-division: Mastigomycotina

Symptoms:

• Water-soaked patches on the basal portion of the stem near the ground level.
• Dark staining of bark, progressing into the wood.
• Bark dries, shrinks, cracks, and shreds in lengthwise vertical strips.
• Exudation of gum from the bark of the trunk.
• Base bark destruction leads to tree death.
• Infected plants may blossom heavily but die before fruit maturity.

Etiology:

• Pathogen Type: Fungus-like organism (Oomycete).
• Survival and Spread: Survives as oospores in infected plant debris or soil. Spreads via waterborne zoospores.
• Entry and Infection:
  • Pathogen enters through wounds or natural openings at the tree base.
  • Infection favored by prolonged contact with water and waterlogged soil conditions.

Disease Cycle:

• Primary Infection: Initiated by oospores present in soil or infected plant debris.
• Secondary Infection: Zoospores dispersed by irrigation water or rain splash.

Favourable Conditions:

• Prolonged trunk contact with water (e.g., flood irrigation).
• Waterlogged areas and heavy soils enhance disease development.

Management:

• Cultural Practices:
  • Select planting sites with good drainage.
  • High budding (30-46 cm above ground) to prevent trunk contact with soil.
  • Use a double ring method for irrigation to avoid wetting the trunk.
• Chemical Control:
  • Soil drenching with 0.2% Metalaxyl.
  • Application of 0.5% Trichoderma viride formulation.

CITRUS CANKER

Causal Organism:

• Xanthomonas axonopodis pv. citri
• Type: Bacterium

Symptoms:

• Minute, water-soaked round yellow spots on leaves, twigs, and fruits.
• Spots enlarge, becoming brown, eruptive, and corky.
• Lesions on leaves are surrounded by a yellow halo.
• Canker lesions on fruits are corky but lack the yellow halo.
• Multiple lesions may coalesce to form patches.

Etiology:

• Pathogen Type: Bacterium.
• Survival and Spread:
  • Survives in infected plant debris, cankers, and nursery stock.
  • Spread through rain splash, irrigation water, and insects (e.g., Citrus leaf miners).
• Entry and Infection:
  • Pathogen enters through stomata or wounds on leaves, twigs, and fruits.
  • Rainy and humid conditions favor bacterial multiplication and spread.

Disease Cycle:

• Primary Infection: From infected plant parts or cankers on twigs.
• Secondary Infection: Spread by splashing rainwater, irrigation water, and leaf miners (Phyllocnistis citrella).

Favourable Conditions:

• Free moisture on plant surfaces for 20 minutes.
• Temperature range of 20-30°C promotes disease initiation and spread.

Management:

• Cultural Practices: Prune and burn all infected twigs before the monsoon season.
• Chemical Control:
  • Spray Streptocycline @ 0.01% + Copper oxychloride @ 0.3% at 10-day intervals.
  • Monthly sprays of Copper oxychloride (0.3%) are effective in disease control.