A) Stem Rot / Foot Rot of Banana

Pathogen: Pythium aphanidermatum

Economic Importance:

• A serious fungal disease affecting banana plants, leading to significant yield losses.
• Most common in 2-3 year-old banana trees.
• Severe in areas with poor drainage and waterlogged conditions.

Symptoms:

i) Stem Symptoms:

• • Water-soaked spots at the ground level of the stem.
  • Spots enlarge and girdle the stem, leading to brown or black rot.
  • The affected area becomes soft and mushy, causing the plant to topple over and die.

ii) Leaf Symptoms:

• • Terminal leaves turn yellow, droop, and eventually fall off.
  • Rapid wilting and drying of leaves as the disease progresses.

iii) Plant Death:

• • Complete plant death occurs when the infection disrupts water and nutrient flow.
  • Stunted growth and poor bunch development are observed in affected plants.

Pathogen Characteristics:

• Pythium aphanidermatum is a soil-borne oomycete pathogen.
• It produces hyaline (transparent), coenocytic (non-septate), and highly branched mycelium.
• The pathogen forms sporangia, which release zoospores that spread in waterlogged soils.
• Oospores act as resting structures, allowing the fungus to survive in soil for long periods.

Favorable Conditions for Disease Development:

• High soil moisture and waterlogged conditions.
• Poorly drained soils and excessive irrigation.
• Warm and humid weather conditions enhance disease severity.

Mode of Spread and Survival:

• Primary Spread: Through infected soil, contaminated planting material, and irrigation water. Zoospores are water-borne and spread rapidly in wet conditions.
• Secondary Spread: Splashing rainwater disseminates the pathogen to nearby plants. Contaminated tools and farm equipment can also spread the disease.
• Survival: Oospores enable the pathogen to survive in soil for extended periods. It persists in infected plant debris and can withstand harsh environmental conditions.

Management Strategies:

i) Cultural Practices:

• • Ensure good drainage to avoid waterlogging.
  • Avoid excessive irrigation and maintain optimum soil moisture.
  • Use disease-free planting material from certified sources.
  • Remove and destroy infected plants and debris to reduce inoculum load.
  • Practice crop rotation with non-host crops to lower pathogen survival.

ii) Chemical Control:

• • Seed treatment with Thiram or Captan (4 g/kg) before planting.
  • Soil drenching with:
    • Copper oxychloride (0.25%)
    • Bordeaux mixture (1%)
    • Metalaxyl (0.1%)

iii) Biological Control:

• • Application of Trichoderma spp. as a biocontrol agent to suppress the pathogen.
  • Mycorrhizal fungi can enhance plant resistance and reduce disease severity.

iv) Resistant Varieties:

• • Planting resistant or tolerant banana cultivars can minimize disease impact.
  • Local adaptability of cultivars should be considered for resistance.

v) Integrated Disease Management (IDM):

• • Combine cultural, chemical, and biological control methods for effective management.
  • Regular monitoring and early detection to control the spread of disease.
  • Sanitation practices, such as disinfecting tools and equipment, help prevent contamination.

B) Papaya Leaf Curl Disease

Pathogen: Papaya Leaf Curl Virus (PaLCV)
Vector: Whitefly (Bemisia tabaci)

Economic Importance:

• Causes significant yield losses due to stunted growth and failure to produce flowers and fruits.
• Affected plants have poor market value due to distorted leaves and unproductive growth.

Symptoms:

i) Leaf Symptoms:

• • Curling, crinkling, and distortion of leaves.
  • Reduction in leaf lamina size.
  • Rolling of leaf margins inward and downward.
  • Thickening of veins on the underside of leaves.
  • Leaves become leathery, brittle, and distorted.

ii) Plant Symptoms:

• • Stunted growth with shortened internodes, giving a bushy appearance.
  • Crowded and smaller leaves due to reduced petiole length.
  • Failure to produce flowers and fruits, leading to yield loss.

Mode of Spread:

• Vector Transmission: Spread by Whitefly (Bemisia tabaci), which acts as the vector.
• Primary Infection: Occurs through feeding of viruliferous whiteflies on healthy plants.
• Secondary Spread: Whiteflies move from infected to healthy plants, causing rapid disease transmission.

Favorable Conditions:

• High temperature (25-35°C) and low humidity favor whitefly population buildup.
• Presence of alternate host plants like tomato, tobacco, and other solanaceous crops nearby.

Management Strategies:

i) Cultural Practices:

• • Uproot and destroy affected plants to reduce the source of infection.
  • Avoid growing tomato, tobacco, and other host crops near papaya fields.
  • Maintain field sanitation by removing weeds that can host whiteflies.
  • Use reflective mulches to repel whiteflies.
  • Plant virus-resistant varieties if available.

ii) Chemical Control:

• • Spray systemic insecticides to control whitefly vectors.
    • Imidacloprid (0.3 ml/l)
    • Thiamethoxam (0.25 g/l)
    • Dimethoate (0.05%)
  • Rotate insecticides to prevent resistance buildup.

iii) Biological Control:

• • Introduce natural enemies like Encarsia formosa (parasitic wasp) to control whitefly populations.
  • Neem oil sprays (2-3%) can be used for eco-friendly vector control.

iv) Physical Control:

• • Use yellow sticky traps to monitor and reduce whitefly populations.
  • Install insect-proof nets in nurseries to prevent vector entry.

Preventive Measures:

• Inspect seedlings for virus symptoms before transplanting.
• Avoid overlapping crops of papaya to minimize whitefly migration.
• Educate farmers on early detection and effective vector management strategies.
• Practice crop rotation with non-host crops to break the virus cycle.

C) Mosaic of Papaya

Pathogen: Papaya Mosaic Virus (PapMV)
Vector: Aphids (e.g., Aphis gossypii, Myzus persicae)

Economic Importance:

• Causes significant yield loss due to reduced photosynthesis and stunted growth.
• Infected plants produce deformed and unmarketable fruits, affecting profitability.

Symptoms:

i) Leaf Symptoms:

• • Mosaic pattern: Alternating patches of light and dark green areas on leaves.
  • Distortion and curling of leaves, especially at the margins.
  • Blistering and crinkling of leaf lamina.
  • Reduction in leaf size, giving a shrunken appearance.

ii) Plant Symptoms:

• • Stunted growth and shortened internodes.
  • Chlorosis (yellowing) of leaves, especially near the veins.
  • Shoots and branches become bushy due to shortened petioles.
  • Reduced flowering and fruiting, leading to lower yield.

iii) Fruit Symptoms:

• • Malformed fruits with irregular shapes.
  • Mosaic mottling on the fruit surface.
  • Hardening of fruit skin, leading to poor quality.
  • Poor flavor and texture in affected fruits.

Mode of Spread:

• Vector Transmission: Spread by Aphids in a non-persistent manner.
• Primary Infection: Occurs when aphids feed on infected plants and transmit the virus to healthy plants.
• Secondary Spread: Aphids migrate to nearby plants, spreading the virus rapidly.

Favorable Conditions:

• Warm temperatures (25-30°C) and high humidity favor aphid multiplication.
• Presence of alternate host plants like cucurbits and solanaceous crops.

Management Strategies:

i) Cultural Practices:

• • Uproot and destroy infected plants to prevent further spread.
  • Maintain field sanitation by removing weeds that host aphids.
  • Isolate papaya fields from susceptible crops like cucurbits.
  • Avoid overlapping crops to minimize aphid migration.
  • Plant resistant varieties if available.

ii) Chemical Control:

• • Spray systemic insecticides to control aphid vectors:
    • Imidacloprid (0.3 ml/l)
    • Thiamethoxam (0.25 g/l)
    • Dimethoate (0.05%)
  • Repeat sprays at 15-day intervals during peak aphid activity.

iii) Biological Control:

• • Release natural enemies like ladybird beetles (Coccinellidae) and parasitic wasps to control aphid populations.
  • Spray neem oil (2-3%) as an eco-friendly insecticide.

iv) Physical Control:

• • Use yellow sticky traps to monitor and control aphid populations.
  • Install insect-proof nets in nurseries to prevent vector entry.

Preventive Measures:

• Inspect seedlings for mosaic symptoms before transplanting.
• Avoid planting near aphid-host crops like cucurbits and solanaceous crops.
• Rogue out infected plants as soon as symptoms appear.
• Educate farmers on early detection and integrated pest management strategies