A) Anthracnose of Guava

Pathogen: Colletotrichum gloeosporioides

Symptoms:

• Appears mainly on mature fruits while still on the tree.
• Sunken, dark-colored necrotic lesions develop on the fruit surface.
• Under humid conditions, lesions are covered with pinkish spore masses.
• As the disease progresses, the small sunken lesions merge, forming large necrotic patches that penetrate the fruit flesh, leading to fruit rot.
• In severe cases, it causes fruit drop and reduces fruit quality.

Pathogen Characteristics:

• Conidia: Hyaline (transparent), aseptate, oval to elliptical in shape.
• Conidiophore: Cylindrical in structure.
• Acervuli: Dark brown to black, appearing on necrotic lesions.

Mode of Spread and Survival:

• The pathogen overwinters on infected plant debris and diseased fruits.
• Conidia are primarily spread by wind and rain splashes.
• High humidity and wet conditions favor the germination and spread of spores.

Favorable Conditions:

• Warm and humid climates are highly conducive to disease development.
• Frequent rainfall and prolonged leaf wetness accelerate infection.

Management:

i) Cultural Practices:

• • Remove and destroy infected plant debris and fallen fruits.
  • Ensure proper pruning to improve air circulation and reduce humidity around the canopy.
  • Practice crop rotation to minimize pathogen build-up.

ii) Chemical Control:

• • Spray Mancozeb 0.25% or Copper oxychloride 0.3% at regular intervals during fruit development.
  • Begin fungicide sprays at the onset of flowering and continue at 10-15 day intervals.

iii) Integrated Disease Management (IDM):

• • Combine cultural practices and chemical control for effective management.
  • Use disease-resistant guava varieties, if available.

Preventive Measures:

• Avoid overhead irrigation to reduce leaf wetness.
• Maintain field hygiene by clearing plant debris and pruning residues.
• Monitor weather conditions to time fungicide applications effectively.

B) Wilt of Guava

Pathogen: Fusarium oxysporum f.sp. psidii and Cephalosporium spp.

Symptoms:

• Yellowing of leaves starting from the older leaves and gradually moving to younger ones.
• Wilting and drooping of leaves leading to premature leaf fall.
• Drying of twigs and branches, often starting from the tips.
• Dark brown discoloration of vascular tissues (when the bark is peeled off).
• Gradual decline of the entire plant leading to death within a few months.
• Affected plants show reduced fruit size and poor fruit quality.

Pathogen Characteristics:

• The pathogen enters through roots and colonizes the vascular system, blocking water and nutrient flow.
• It produces microsclerotia that can survive in soil for long periods, making the disease persistent.

Mode of Spread and Survival:

• The fungus persists in the soil as chlamydospores or microsclerotia.
• Infected plant debris and soil particles carry the pathogen to new areas.
• It spreads through irrigation water, tools, and human activities.

Favorable Conditions:

• Warm temperatures (25-30°C) and high soil moisture favor disease development.
• Poorly drained soils and over-irrigation increase disease incidence.

Management:

i) Cultural Practices:

• • Practice crop rotation with non-host crops to reduce pathogen load.
  • Remove and destroy infected plants to prevent the spread of the disease.
  • Improve soil drainage to avoid waterlogging.
  • Use disease-free planting material from certified nurseries.

ii) Soil Management:

• • Soil solarization: Covering soil with transparent polyethylene sheets during hot months to kill soil-borne pathogens.
  • Application of organic amendments like neem cake or mustard cake can help suppress the pathogen.

iii) Chemical Control:

• • Drenching soil with Carbendazim (0.1%) or Thiophanate-methyl (0.1%) around the root zone.
  • Pre-planting soil fumigation with formalin (1-2%) can reduce the pathogen load in the soil.

iv) Biological Control: Use of biocontrol agents like Trichoderma harzianum and Pseudomonas fluorescens to suppress the pathogen.

v) Integrated Disease Management (IDM): Combine cultural practices, soil management, chemical control, and biocontrol agents for effective disease management.

Preventive Measures:

• Avoid excessive irrigation to reduce soil moisture.
• Disinfect tools and equipment to prevent the spread of the pathogen.
• Monitor fields regularly for early detection and management.