A) Scab

Host Plants:

• Apple (Venturia inaequalis)
• Pear (Venturia pirina)

Symptoms:

• On Leaves:
  • Circular, olive-green to black spots on upper surfaces, leading to puckering, twisting, and yellowing.
  • Severe infections cause premature leaf drop.
• On Flowers: Infected flower stems may cause flower drop.
• On Fruits: Dark, scabby lesions leading to cracking and distortion. Severe infections cause fruit drop and secondary infections.

Etiology:

• Causal Organism: Venturia inaequalis (Apple), Venturia pirina (Pear)
• Sub-division: Ascomycotina
• Primary Inoculum: Ascospores from Pseudothecia on fallen leaves.
• Secondary Inoculum: Windborne conidia.

Disease Cycle:

• Primary Infection: Ascospores released from Pseudothecia on fallen leaves in spring. Infection occurs on young leaves and fruits under wet, cool conditions.
• Secondary Infection: Conidia spread by wind, causing secondary infections throughout the growing season.

Favorable Conditions:

• Wet and cool weather with temperatures between 12°C to 24°C.
• Leaf wetness for at least 6 hours.

Management:

1. Cultural Practices: Clean cultivation and removal of fallen leaves Prune trees to improve air circulation.
2. Resistant Varieties: Apple: Emira, Red Free, Ambstraking, Ambroyal, Ambrich, Ambred. Pear: Resistant cultivars recommended.
3. Chemical Control:
   • Captan (0.2%) or Dodine (0.25%) at short intervals after petal fall.
   • Difolaton (0.3%) at green bud stage followed by Captan (0.2%) at petal fall.
4. Spray Schedule:
   • Silver Tip Stage: Captofol (0.2%) or Captan (0.3%).
   • Pink Bud Stage: Captan (0.2%) or Mancozeb (0.3%).
   • Petal Fall: Carbendazim (0.5%).
   • After 10 Days: Captan (0.2%).
   • After 15 Days: Mancozeb (0.3%).
   • Fruit Set Stage: Captofol (0.15%).

B) Powdery Mildew

Host Plants:

• Apple (Podosphaera leucotricha)
• Grapevine (Uncinula necator)
• Cucurbits (Erysiphe cichoracearum, Sphaerotheca fuliginea)

Symptoms:

• On Leaves:
  • White or grey powdery masses on the underside.
  • Twisting, curling, and narrowing of leaves.
  • In severe cases, leaves turn yellow and drop.
• On Twigs: White powdery coating leading to stunted growth. Twig dieback in severe infections.
• On Fruits: Deformation and cracking of young fruits. Rough, russeted surfaces in mature fruits.
• On Flowers: Flower shedding and poor fruit set.

Etiology:

• Causal Organism:
  • Podosphaera leucotricha (Apple)
  • Uncinula necator (Grapevine)
• Sub-division: Ascomycotina
• Primary Inoculum: Mycelium in dormant buds.
• Secondary Inoculum: Airborne conidia.

Disease Cycle:

• Primary Infection: Dormant mycelium in infected buds becomes active in spring. Infects new shoots, leaves, and flowers.
• Secondary Infection: Conidia produced on infected parts spread by wind, causing repeated cycles of infection.

Favorable Conditions:

• Cool, dry weather with temperatures of 27-31°C.
• Relative Humidity up to 91%.

Management:

1. Cultural Practices: Prune infected shoots and buds during dormancy. Ensure good ventilation and air circulation in orchards.
2. Resistant Varieties: Apple: Maharaja Chunth, Golden Chinese. Crab Apple: Yantarka Altaskya, Dolgoe.
3. Chemical Control:
   • Pre-bloom Spray: Lime Sulphur (1:60).
   • Post-bloom Sprays:
     • Dinocap (0.05%) or Wettable Sulphur for effective control.
     • Karathane (0.1%) or Calixin (0.1%) for grapevine powdery mildew.
4. Integrated Disease Management (IDM): Alternate fungicides to avoid resistance buildup. Combine chemical and cultural practices for effective control.

C) Fire Blight of Apple

Causal Organism: Erwinia amylovora

Symptoms:

• Affected Tissues: All above-ground parts, including blossoms, fruits, shoots, branches, and rootstock near the graft union.
• Blossom Clusters and Young Shoots: Floral receptacle, ovary, and peduncles become water-soaked and dull grayish-green. Later, they shrivel and turn brown to black.
• Shoot Symptoms:

Tips of shoots wilt rapidly, forming a “shepherd’s crook.”

• • Leaves on diseased shoots show blackening along the midrib and veins before becoming fully necrotic.
  • Numerous diseased shoots give the tree a burnt and blighted appearance.
• Ooze Production: Milky-colored, sticky ooze may appear on infected parts, turning brown upon exposure to air.

Disease Cycle:

• Primary Infection: Bacteria overwinter at the margins of cankers, in buds, and possibly in apparently healthy woody tissue.
• Secondary Infection: Spread by insects like bees, flies, and ants.

Favorable Conditions: Warm and humid climate promotes disease development.

Management:

1. Cultural Practices:
   • Prune blighted twigs, branches, cankers, and even entire trees during winter.
   • Cut about 30 cm below the visible infection point.
   • Disinfect pruning tools after each cut using 10% sodium hypochlorite.
2. Insect Control: Manage insect vectors to reduce bacterial spread.
3. Resistant Varieties: Plant resistant apple varieties to minimize disease impact.
4. Chemical Control:
   • Dormant Sprays: Copper sulfate or Bordeaux mixture.
   • Blossom Sprays: Bordeaux mixture or Streptomycin (most effective).

D) Crown Gall

Causal Organism: Agrobacterium tumefaciens

Symptoms:

• Outgrowths on Stem and Roots:
  • Occur near the soil line.
  • Galls are spherical, white, or flesh-colored when young.
  • Become hard, corky on woody stems, and appear knobby and knotty.
• Plant Growth: Infected plants are stunted with chlorotic (yellowed) leaves.

Management:

1. Regulatory Measures: Implement quarantine and sanitation practices to prevent disease spread.
2. Crop Rotation: Rotate with non-host crops like maize or other grain crops to reduce pathogen load.
3. Avoid Injuries: Minimize injuries to roots and lower stem parts, which act as entry points for bacteria.
4. Biological Control: Use Agrobacterium radiobacter (Strain K1026) on fresh wounds to prevent gall formation.
5. Chemical Control: Penicillin or Vancomycin offers partial control.