San Jose Scale
Quadraspidiotus perniciosus
📖 Description
San Jose Scale (SJS) is one of the most destructive scale insect pests of apple and other fruit trees across the Indian subcontinent, particularly in Himachal Pradesh, Jammu & Kashmir, and Uttarakhand. The pest is exceptionally difficult to control because the waxy covering of settled nymphs and adults protects them from contact insecticides. The only vulnerable stage is the crawler (first instar nymph), which is mobile and unprotected for just 24-48 hours before settling. Dormant oil spray in winter suffocates overwintering scales and is the most effective single control measure. Monitoring crawler emergence with double-sided tape wrapped around branches is essential for timing crawler-stage insecticide applications. SJS has over 700 host plants and can kill mature trees within 2-3 years if unmanaged. Quarantine of nursery material is critical because the pest spreads primarily through infested planting stock.
⚠️ Symptoms to watch for
- Reddening of tissue around scales on fruits and leaves
- grey crusty patches on bark and fruits
- deformed and stunted fruits
- reduced fruit size and quality
- dieback of branches
- tree decline in heavy infestation
- complete crop loss possible in severe cases
🩹 Treatment
- Apply dormant spray of horticultural oil 2% in winter
- spray neem oil 5ml/L during crawler stage
- apply systemic insecticides at crawler emergence
- conserve parasitic wasps
- prune and destroy infested branches
🌿 Organic treatments
- Apply dormant spray of horticultural oil 2% in winter before bud break
- spray neem oil 5 ml/L with sticker during crawler stage (monitor with double-sided tape)
- apply Lecanicillium lecanii @ 5 g/L
- release Encarsia perniciosi and Aphytis spp. parasitoids
- prune and burn heavily infested branches
- scrub bark with stiff brush to remove scales
🧪 Chemical treatments
- Dormant spray with Horticultural mineral oil 2%
- Chlorpyrifos 20 EC @ 2 ml/L at dormant stage
- Buprofezin 25 SC @ 2 ml/L during crawler emergence
- Imidacloprid 17.8 SL @ 0.3 ml/L
- Spirotetramat 240 SC @ 0.5 ml/L (systemic — effective against settled nymphs)
🛡️ Prevention
- Use certified scale-free nursery material
- apply dormant oil spray in winter before bud break
- monitor crawler emergence with double-sided tape wrapped around branches
- prune and destroy heavily infested branches
- inspect orchards weekly during spring
- conserve parasitic wasps (Encarsia, Aphytis) by avoiding broad-spectrum insecticides
- paint pruning wounds with Bordeaux paste
- quarantine new plant material for one season
🪴 Affected plants
- Apple (Primary)
- Pear
- Peach
- Plum
- Cherry
- Apricot
- Many Ornamental Trees and Shrubs (over 700 host plants)
🦋 Natural predators
- Encarsia perniciosi
- Aphytis spp.
- Ladybird Beetles
- Green Lacewings
- Predatory Bugs
🌱 Host plants
- Malus domestica
- Pyrus communis
- Prunus persica
- Prunus domestica
- Prunus avium
🔄 Lifecycle
- Female lays 100-400 eggs under her protective scale.
- Eggs hatch in 7-14 days.
- Crawlers disperse and settle within 24-48 hours, then secrete their waxy covering.
- Nymphs pass through 2 instars over 20-40 days.
- Adult females live 30-60 days; males are tiny, winged, and short-lived.
- Total life cycle 35-50 days; 3-4 generations per year in temperate conditions.
📅 Season
- Year-round, crawler emergence peaks Apr-May, Jun-Jul, and Aug-Sep
🔎 Appearance
- Tiny, circular, greyish-black scale insects with a yellowish central spot (nipple).
- They appear as small bumps on bark, leaves, and fruits.
- Crawlers (first instar nymphs) are tiny, yellow, and mobile.
- They secrete a waxy covering that protects them from contact insecticides.
💥 Damage level
- High
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian Subcontinent
- Worldwide Fruit-Growing Regions
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