Divisi
Cashew stem and root borer
Plocaederus ferrugineus · Insect
Photo: Len Worthington · CC BY-SA 2.0
The cashew stem and root borer is the grub of a large reddish-brown longhorn beetle (Plocaederus ferrugineus). The beetle lays its eggs in bark cracks at the base of cashew trees; the grubs then tunnel into the collar (where the trunk meets the ground), the trunk base and the main roots, chewing through the living layer just under the bark that carries the tree's food and water. The damage stays hidden inside the wood until the leaves yellow and the branches die back — and a single grub can kill a full-grown, bearing tree. Stressed, neglected orchards, where dead trunks are left standing as beetle nurseries, suffer worst.
Len Worthington · CC BY-SA 2.0
Why it matters
The stem and root borer is a tree-killer, not just a leaf-nibbler. Its grubs eat hidden inside the base and roots of your cashew, ring-cutting the very pipes that carry the tree's food and water, and a single grub can kill a full-grown, bearing tree. In a bad outbreak it can take more than half your trees (up to 60%), and each tree it kills is gone for good, along with all the years of nuts it would have given. Worst of all, by the time the leaves yellow and the tree wilts the grub is deep in the wood where no spray can reach — so catching it early, at the first gum and sawdust, is your only real chance.
When to act
any tree with fresh frass, gum ooze or bore holes at the trunk base or collar
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full cashew stem and root borer field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to cashew stem and root borer — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify cashew stem and root borer?
The first sign is at the foot of the tree, not the leaves. Look at the collar — where the trunk meets the ground — for blobs of sticky gum (resin) oozing out and little piles of reddish-brown, sawdust-like frass (the chewed wood and droppings the grub pushes out as it tunnels). You will also see bore holes in the bark, often with frass spilling from them.
When should I take action against cashew stem and root borer?
any tree with fresh frass, gum ooze or bore holes at the trunk base or collar
How do I control cashew stem and root borer?
Prevent it — keep trees strong and the orchard clean. A vigorous, well-watered, well-fed tree shrugs the borer off; a stressed, neglected one invites it. Mulch and water in dry spells and feed your trees, and never leave a dead or dying tree standing — a dead trunk is a beetle nursery. Cut out and burn dead and badly-infested trees to wipe out the breeding sites (this is your strongest, highest-success control).
Which crops does cashew stem and root borer affect?
Among the crops covered here: Cashew.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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