Cashew Stem and Root Borer
Plocaederus ferrugineus
📖 Description
Cashew Stem and Root Borer is the most destructive pest of cashew in the Indian subcontinent, causing annual losses of 10-20% of trees in endemic zones of Kerala, Karnataka, Goa, Maharashtra, Andhra Pradesh, Odisha and West Bengal. The grub tunnels through the bark and wood at the collar region, girdling the tree and causing slow decline and eventual death. Once a tree is infested, saving it is difficult — prevention is the only sustainable strategy. Regular trunk swabbing with insecticide paste, prompt removal of infested trees, and avoidance of mechanical injuries are essential. The pest prefers stressed trees (drought, waterlogging, nutrient deficiency), so maintaining vigorous crop growth is critical. Metarhizium anisopliae paste application is emerging as a promising organic alternative.
⚠️ Symptoms to watch for
- Bark drying and cracking at collar region, extrusion of frass and wood powder from holes at base of trunk, yellowing and wilting of canopy, gum exudation from trunk, sudden death of tree in 6-12 months, mortality 5-20% in neglected gardens
🩹 Treatment
- Locate and kill grubs by inserting wire through bore holes, swab trunk with Carbaryl paste (1:1 with water) up to 1 m height, apply Chlorpyriphos 2 ml/L as collar drench, prune and destroy infested branches, remove completely dead trees
🌿 Organic treatments
- Locate and mechanically kill grubs with hooked wire, apply Metarhizium anisopliae paste (50 g/L) on collar region, swab with neem oil + 5% Beauveria bassiana paste, apply entomopathogenic nematodes (Steinernema) @ 1 billion/ha to root zone, paint collar with cow dung + neem oil paste
🧪 Chemical treatments
- Chlorpyriphos 20 EC @ 2 ml/L (collar drench), Carbaryl 50 WP paste @ 50 g/L water (trunk swab), Monocrotophos 36 SL @ 1 ml/L (swab), Imidacloprid 17.8 SL @ 0.5 ml/L (soil drench)
🛡️ Prevention
- Avoid injuries to trunk and roots during cultivation, maintain proper drainage, swab trunks with Carbaryl paste twice a year (pre-monsoon and post-monsoon), remove and burn dead and dying trees before adult emergence, regular monitoring of trunk for frass, plant at recommended spacing to avoid stress
🪴 Affected plants
- Cashew, Mango (occasionally), Rubber (occasionally)
🦋 Natural predators
- Woodpeckers, Predatory Ants, Carabid Beetles, Entomopathogenic Fungi, Spiders
🌱 Host plants
- Anacardium occidentale, Mangifera indica, Hevea brasiliensis
🔄 Lifecycle
- Female lays 200-400 eggs in bark crevices and collar region.
- Eggs hatch in 6-10 days.
- Grubs tunnel and feed inside bark and wood for 4-7 months through 5-6 instars.
- Pupation inside cocoon in stem, lasting 15-25 days.
- Adult lifespan 30-60 days.
- Total life cycle 6-9 months; 1-2 generations per year.
📅 Season
- Year-round, adult emergence peaks Apr-Jun and Sep-Nov
🔎 Appearance
- Adult is a large, reddish-brown to dark brown longicorn beetle with long antennae (longer than body in males).
- Grubs are large, creamy-white, elongate, legless with a brown head.
- Pupae are pale yellow inside a cocoon of frass and wood fibers inside the stem.
💥 Damage level
- Severe
🔁 Reproduction rate
- Slow
🗺️ Geographic regions
- Indian Subcontinent
- South Asia
- Southeast Asia
- Africa
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