Apple scab
A fungal disease that spreads by airborne ascospores from overwintered leaf litter in spring, causing olive-black velvety lesions on leaves and scabby, cracked spots on fruit that make it unsellable. The spray programme from green-tip onward is the backbone of commercial apple production in India.
- Pathogen
- Venturia inaequalis (ascomycete fungus)
- Spreads via
- Airborne ascospores in spring, rain-splashed conidia later
- Worst period
- Green-tip through June (primary); continuing with rain through harvest
- Best defence
- Timed fungicide sprays + leaf-litter sanitation + resistant varieties
Overview
Apple scab, caused by the ascomycete fungus Venturia inaequalis, is the single most economically damaging disease of apple in India's north-western Himalayan growing belt — Jammu & Kashmir, Himachal Pradesh and Uttarakhand. Uncontrolled scab can destroy 70–100% of the marketable crop in a wet season. The fungus overwinters as pseudothecia (tiny fruiting bodies) in fallen, infected leaf litter on the orchard floor, and releases ascospores into the air from green-tip through petal-fall whenever rain wets the litter for a sufficient period — this primary infection window is the one the spray programme targets.
Once a primary infection establishes on a leaf or young fruit, it produces conidia (asexual spores) that are rain-splashed to nearby leaves and fruit throughout the growing season, causing secondary infections that build up the epidemic. Every fungicide spray after petal-fall is chasing these secondary cycles. The visible symptom is a velvety, olive-green to black spot on the upper leaf surface and a scabby, rough, cracked lesion on the fruit skin — even light infection downgrades fruit from A-grade to processing or cull, and heavy infection causes premature leaf drop, weakening the tree for the following season.
How to identify it
- Olive-green to dark-brown or black velvety spots appear on the upper surface of young leaves, often along veins — the velvety texture is spore production visible to the naked eye.
- Severely infected leaves curl, yellow and drop prematurely, thinning the canopy by mid-season.
- Fruit lesions start as small, dark, rough spots that enlarge into scabby, corky patches — the skin cracks open as the fruit grows, making it unsellable even if the flesh underneath is sound.
- Late-season or storage scab appears as tiny black pinpoint spots (pin-point scab) on fruit that looked clean at harvest — caused by conidia that landed just before picking and developed slowly in cold storage.
- On young shoots and twigs, small raised blisters or cankers may form, carrying the fungus into the next season.
Why it happens
- The fungus overwinters in fallen infected leaves on the orchard floor — every infected leaf left on the ground is a spore source for the following spring.
- Ascospores are released from the leaf litter whenever rain wets it for at least a few hours during the green-tip-through-petal-fall window, and are carried by wind to developing leaves and fruitlets.
- Cool, wet spring weather — exactly the conditions in India's apple belt during March–May — extends the infection period and drives primary infections.
- Dense, unpruned canopies trap moisture and slow leaf drying, giving conidia the prolonged wetness they need to germinate and infect during secondary cycles through the growing season.
- Susceptible varieties planted without a spray programme — particularly Red Delicious and its sports, which dominate Indian orchards and have no scab resistance — are a recipe for severe epidemics.
Organic and cultural control
- Collect and destroy fallen infected leaves after harvest — raking, composting, or flail-mowing leaf litter reduces the next spring's ascospore load by 80–90% if done thoroughly.
- Apply 5% urea spray to the fallen leaf litter on the orchard floor in late autumn (after the leaves have dropped) to accelerate decomposition and reduce pseudothecia formation.
- Prune to an open canopy that allows rapid air circulation and leaf drying after rain — a wet leaf is the infection event.
- Plant scab-resistant varieties (Firdous, Shireen, Akbar from SKUAST-Kashmir) where possible, especially in new plantings — resistance eliminates the need for most of the spray programme.
- Copper-based sprays (Bordeaux mixture) at green-tip provide some early-season protection and are organic-compatible, though alone they are weaker than synthetic fungicides.
Chemical control
- The spray programme begins at green-tip (when the first green leaf tissue is visible in the bud) and continues through petal-fall and into the cover-spray period — this is not a single spray but a season-long schedule of 8–12 fungicide applications.
- Pre-bloom sprays (green-tip, pink-bud, full-bloom, petal-fall) target primary ascospore infections — these are the most critical sprays of the season; missing the green-tip spray in a wet year is hard to recover from.
- Post-bloom cover sprays at 10–15 day intervals target secondary conidia infections on developing fruit.
- Rotate fungicide groups to delay resistance: alternate contact fungicides (mancozeb, captan) with systemic/translaminar ones (myclobutanil, penconazole, flusilazole + carbendazim, difenoconazole) rather than repeating the same active ingredient.
- Confirm the current recommended spray schedule and products with SKUAST-Kashmir, YSPUHF Nauni (Himachal Pradesh), or your local KVK — the schedule is adjusted each season based on weather.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Varieties to consider
Named seed varieties whose resistance or susceptibility to this problem is documented on their own variety page.
Frequently asked questions
Can apple scab be cured once it appears on the fruit?
No — once the scabby lesion has formed on the fruit skin, no spray will remove it. The fruit is permanently downgraded. The spray programme is preventive: it stops new infections from establishing, but cannot reverse existing ones.
Will removing fallen leaves really reduce scab?
Yes — thorough leaf-litter removal or destruction after harvest can reduce the next spring's ascospore load by 80–90%. It is the single most effective cultural practice against apple scab, because the fungus overwinters almost exclusively in fallen leaves.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.