Divisi
Scale insects
· Insect
Photo: Toby Hudson · CC BY-SA 3.0
Scale insects are tiny sap-sucking bugs that clamp onto the twigs, leaf veins and fruit of trees and bushes — citrus, mango, coffee, guava and cassava among them — and sit there for life under a waxy shell or crust no bigger than a pinhead. Armoured scales wear a hard, separate shield; soft scales are dome-shaped and dribble sticky honeydew (sugary droppings) that blackens leaves and fruit with sooty mould. They breed fast in hot, dry, dusty weather, are herded and defended by ants, and once they encrust a tree they sap its strength, kill back its twigs and blemish the fruit.
Scot Nelson · CC0 
Scot Nelson · CC0
Why it matters
A heavy scale attack can strip up to 40% of your harvest — close to half the fruit on a badly hit tree — leaving fruit blackened and blemished so it won't sell, and shoots that yellow and die back. It creeps up on you: the insects sit dead still under a waxy armour that shrugs off most sprays, ants guard and spread them, and on a tree crop they carry over season after season — so by the time you spot the black sooty mould, the colony is already huge. That is why scale is far cheaper to stop early than to clear once it has crusted over your trees.
When to act
scale colonies encrusting shoots or fruit, sooty mould developing, or twig dieback appearing
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 scale insects field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to scale insects — 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 scale insects?
The first thing you'll notice is usually the mess, not the insect. Leaves and fruit turn sticky and shiny with sugary droppings (honeydew — the clear syrup the scales dribble out), then go black as if dusted with soot (sooty mould, a harmless mould that grows on the honeydew). Watch too for ants streaming up and down the trunk, yellowing leaves that drop early, bare dying twig-ends (dieback), and dull, blackened fruit that fetches a poor price.
When should I take action against scale insects?
scale colonies encrusting shoots or fruit, sooty mould developing, or twig dieback appearing
How do I control scale insects?
Prevent it — start clean and keep trees strong. Plant only clean, scale-free seedlings, cuttings and budwood — scale barely travels on its own, so it mostly arrives on infested plants, tools and clothes. Keep trees vigorous and unstressed: water them through dry spells, rinse road dust off the leaves, and go easy on nitrogen fertiliser (soft, lush growth pulls scale in). Prune out the worst-encrusted twigs and dead wood, then burn or bury the prunings — never leave them lying under the tree.
Which crops does scale insects affect?
Among the crops covered here: Cassava, Guava, Mango.
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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