Cashew stem and root borer
A long-horned beetle grub that tunnels through the trunk and root just below the collar, cutting off sap flow — the leading cause of standing tree death in Indian cashew plantations.
- Pest
- Plocaederus ferrugineus (long-horned beetle)
- Damages
- Trunk & root tissue at the collar region
- Peak activity
- April–May and October–November
- Main risk
- Girdled trunk; standing tree death
Overview
Cashew stem and root borer (CSRB), Plocaederus ferrugineus, is widely regarded as the single most destructive pest of cashew across India's growing belt. The adult beetle lays eggs in bark crevices and wounds near the collar region (where trunk meets root); the grub that hatches bores into the fresh tissue and feeds on the phloem and xylem of the trunk and root, cutting irregular tunnels as it grows. Because this tunnelling arrests the movement of sap and nutrients right at the base of the tree, a heavily infested tree first shows a yellowing, thinning canopy and then dies outright, often looking otherwise healthy from a distance until the damage is already extensive.
The clearest early warning signs are gum (resin) oozing from cracks in the bark near the base, and a fine, sawdust-like frass pushed out of bore holes at ground level or just above it — both worth checking for on a monthly walk through the plantation, particularly in April–May and October–November when adult activity peaks. Because a badly infested tree is very hard to save once tunnelling is extensive, management leans heavily on early detection, mechanical destruction of grubs in fresh bore holes, and preventive trunk treatment, rather than waiting for canopy symptoms to confirm the diagnosis.
How to identify it
- Gum (resin) oozing from cracks and holes in the bark near the base of the trunk.
- Fine, sawdust-like frass pushed out of bore holes at or just above ground level.
- A yellowing, progressively thinning canopy on an otherwise apparently healthy-looking tree.
- Irregular tunnels visible in the phloem and xylem if the bark near the collar is carefully peeled back for inspection.
What causes it and when
- The grub of the long-horned beetle Plocaederus ferrugineus, which the adult lays as eggs in bark crevices and wounds near the collar.
- The grub bores into fresh tissue and feeds on phloem and xylem of the trunk and root, extending irregular tunnels as it grows.
- Adult beetle activity, and therefore fresh egg-laying, peaks around April–May and again in October–November.
- Trees already weakened or wounded — by mechanical injury, other stress or poor vigour — are more attractive to egg-laying females.
Cultural & organic control
- Inspect the trunk base monthly during April–May and October–November for eggs, fresh gum and frass.
- Brush the basal trunk region up to about 2 m height with a hard nylon brush during peak activity to dislodge eggs before they hatch.
- Where a bore hole is found early, mechanically remove the grub, or insert a wire/clutch cable into the hole to kill it directly.
- Remove and destroy dead or beyond-recovery trees at least once every six months so they do not keep breeding fresh beetles.
- Apply neem seed kernel extract (5%) or neem oil to the trunk region as part of a preventive, low-toxicity routine.
Chemical control
- Swab the basal trunk region with a coal tar and kerosene mixture (roughly 1:2) twice a year, timed to March–April and November–December, as a preventive barrier against fresh egg-laying.
- Where infestation is confirmed, a recommended insecticide such as chlorpyrifos applied to the trunk region has shown good recovery in infested trees when used early.
- Chemical trunk treatment works best as prevention or on freshly detected infestation — it cannot recover a tree already girdled through.
- Confirm the current recommended product, concentration and safe-use precautions for cashew stem borer with your local KVK or the Directorate of Cashew Research, Puttur.
Prevent it coming back
- Keep a fixed monthly inspection routine through both peak activity windows every year, not just after damage is suspected.
- Maintain overall tree vigour and avoid mechanical wounds at the collar, since stressed and injured trees attract more egg-laying.
- Remove and destroy severely infested or dead trees promptly so they stop seeding the next generation of beetles.
- Repeat the preventive trunk swab/brush routine every year rather than only after an outbreak is already visible.
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
My cashew tree's canopy is yellowing and thinning even though I see no obvious damage. Could it be stem borer?
Yes, that is a classic pattern — cashew stem and root borer tunnels inside the trunk and root at the collar, cutting off sap flow before any dramatic external damage is visible. Check the base of the trunk closely for gum oozing from bark cracks and fine, sawdust-like frass near ground level; both are the earliest reliable warning signs, well before the canopy symptom becomes obvious.
Why is this pest so hard to control once it is established?
Because the grub feeds hidden inside the trunk and root, tunnelling through the phloem and xylem that carry the tree's sap and nutrients. By the time frass and gum are obvious at the base, tunnelling is often already extensive, and a badly girdled tree usually cannot recover. That is why management focuses on monthly inspection during the beetle's two peak activity windows (April–May and October–November), preventive trunk treatment, and destroying grubs the moment a fresh bore hole is found — waiting for canopy symptoms is usually too late.
Does removing one badly infested tree really help the rest of the plantation?
Yes — a dead or dying, heavily infested tree left standing keeps producing adult beetles that go on to lay eggs on neighbouring healthy trees. Removing and destroying severely infested or dead trees at least every six months is a standard recommendation specifically to cut this source of re-infestation for the rest of the plantation.
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.