📈 Diseases of Apple — Scab, Fire Blight, Canker

Apple (Malus domestica) is the most important temperate fruit crop in India, grown primarily in Jammu & Kashmir, Himachal Pradesh, and Uttarakhand. Apple orchards face several serious diseases that affect productivity and fruit quality.

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Apple Scab

Causal Organism: Venturia inaequalis (Cooke) Wint. (anamorph: Spilocaea pomi)

Apple scab is the most economically important disease of apple globally.

Symptoms

• Olive-green to dark brown, velvety lesions on the upper surface of leaves
• Lesions become corky and raised as they mature
• On fruits, dark, scabby, circular spots that crack upon fruit enlargement
• Severely affected fruits become misshapen and may drop prematurely
• Twig lesions appear as blistered, scab-like patches

Disease Cycle

The fungus overwinters as pseudothecia in fallen infected leaves on the orchard floor. In spring, ascospores are released during rain and initiate primary infections on emerging leaves and blossoms. Secondary spread occurs through conidia produced on lesions.

Management

Strategy	Details
Cultural	Rake and destroy fallen leaves; apply urea (5%) to leaf litter to hasten decomposition
Chemical	Spray Mancozeb (0.25%) or Dodine at green tip; follow with Myclobutanil during bloom
Resistant cultivars	Prima, Priscilla, Liberty, Florina
Spray schedule	Begin at green-tip stage and continue until 2-3 weeks after petal fall

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Fire Blight

Causal Organism: Erwinia amylovora (Burrill) Winslow et al. (Bacterium)

Fire blight is a highly destructive bacterial disease that can kill entire trees rapidly.

Symptoms

• Blossoms turn water-soaked, then brown-black, and wilt ("blossom blight")
• Infected shoot tips bend into a characteristic "shepherd's crook"
• Bark becomes sunken and dark at canker margins, often with bacterial ooze droplets
• Leaves turn brown-black but remain attached, giving a scorched or "fire-burnt" appearance
• Cankers on main branches and trunk can girdle and kill the tree

Spread

Bacterial ooze is spread by rain splash, insects (especially bees during bloom), and pruning tools. Warm, humid weather (24-28 degrees C) during flowering is highly conducive.

Management

• Prune infected branches at least 30 cm below the visible margin of infection
• Disinfect pruning tools with 70% alcohol or 10% bleach between cuts
• Spray Streptomycin (100 ppm) during bloom in high-risk orchards
• Avoid excessive nitrogen fertilisation that promotes succulent, susceptible growth
• Remove fire blight cankers during dormant-season pruning

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Apple Canker

Causal Organism: Neonectria ditissima (Tul. & C. Tul.) Samuels & Rossman (syn. Nectria galligena)

Symptoms

• Sunken, elliptical cankers on branches and trunk with concentric rings of callus tissue
• Bark cracks and peels away, exposing dead wood
• Bright red perithecia (fruiting bodies) develop on canker margins
• Girdled branches die back; young trees may be killed

Disease Cycle

The fungus enters through wounds (pruning cuts, leaf scars, insect damage). Ascospores and conidia are released during wet weather and infect wound sites.

Management

• Cut out cankers well beyond the diseased tissue and treat wounds with wound-sealing paint
• Spray Copper oxychloride (0.3%) after leaf fall and at bud break
• Avoid pruning during wet weather to reduce infection risk
• Select well-drained orchard sites and maintain tree vigour

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Summary Cheat Sheet

Disease	Causal Organism	Hallmark Symptom	Core Management
Apple scab	Venturia inaequalis	Olive-brown velvety lesions on foliage and fruit	Litter sanitation + fungicide schedule
Fire blight	Erwinia amylovora	Shepherd's crook and scorched shoots	Pruning, disinfection, and bloom protection
Apple canker	Neonectria ditissima	Sunken concentric cankers on wood	Canker removal + copper sprays

References

2 sources • [1] [2]

[1]

Indian Council of Agricultural Research (ICAR)

Official

[2]

CABI Crop Protection Compendium

Website