Sooty mould
A black, sooty coating that follows a hopper or scale attack — the mould itself is harmless to attack directly; controlling the insect underneath clears it.
- Cause
- Fungus growing on insect honeydew
- Not a direct infection
- Follows hopper/scale/mealybug attack
- Main effect
- Blocks light; blackens fruit and leaf
- Fix
- Control the honeydew-producing insect
Overview
Sooty mould is a black, powdery fungal growth that appears on leaves, twigs and fruit — but unlike most diseases, it is not directly infecting the plant. It grows on honeydew, the sticky, sugary liquid that sap-sucking insects such as mango hopper, mealybugs and scale insects excrete as they feed. Wherever that honeydew lands, the mould can grow on top of it.
The black coating blocks sunlight from reaching the leaf surface, which can weaken the tree over time in a heavy, repeated attack, and it makes fruit and panicles look dirty and unsellable even though the mould itself does not rot the tissue underneath. Because the mould only grows where honeydew is present, the fix is always to control the insect producing the honeydew — once the insect is controlled and no fresh honeydew is produced, the old mould weathers off on its own with rain and time.
How to identify it
- A black, powdery or crusty coating on the upper surface of leaves, on panicles (flower clusters) and sometimes on fruit.
- It usually follows, and is found alongside, an attack of mango hopper, scale insects or mealybugs — check the shoots and leaf undersides for these insects.
- The coating can often be rubbed or scraped off, revealing a green (though light-starved) leaf underneath rather than a rotted one.
- Fruit coated in sooty mould looks dirty and unsellable even though the mould itself has not rotted the flesh.
What causes it and when
- A fungus growing on honeydew — the sticky, sugary liquid excreted by sap-sucking insects such as mango hopper, scale insects and mealybugs as they feed.
- It is most common and worst during and after a heavy hopper attack at flowering, since hoppers produce large amounts of honeydew right when the panicles are most exposed.
- Wherever honeydew drips or is left behind — leaves below an infested shoot, fruit hanging under a heavily infested panicle — mould can grow on it.
- It builds up over the season if the insect causing it is not controlled, since fresh honeydew keeps feeding fresh mould growth.
Cultural & organic control
- Control the sap-sucking insect responsible (mango hopper, scale or mealybug) — this stops fresh honeydew and is the real fix, not a direct spray on the mould.
- Conserve natural predators of hoppers and scale (ladybird beetles, lacewings, spiders) by avoiding unnecessary broad-spectrum spraying, since they help keep the insect numbers down on their own.
- A strong jet of water can physically wash off some of the mould and honeydew from reachable branches, though this is cosmetic, not a cure.
- Prune out and remove very heavily infested twigs where practical, since they carry both the insect and the worst mould buildup.
Chemical control
- There is no fungicide targeted at the mould itself that makes sense here — spraying a fungicide without controlling the insect leaves the honeydew supply untouched and the mould keeps regrowing.
- Spray a recommended insecticide against the specific sap-sucker involved (see the hopper, mealybug or scale guide for that insect’s dose and timing) at the stage it is most vulnerable — for hopper, that is around panicle emergence.
- Once the insect is controlled, the old sooty mould gradually weathers and washes off in rain over the following weeks without further treatment.
- Confirm the current recommended insecticide and dose for your area with your local Krishi Vigyan Kendra (KVK).
Prevent it coming back
- Scout for mango hopper, scale and mealybug regularly, especially from panicle emergence through fruit set, and treat them before honeydew and mould build up.
- Keep the canopy open with proper pruning so spray coverage is good and natural predators can move through the tree.
- Treat sooty mould as a warning sign, not the problem itself — a mango tree that keeps getting sooty mould has an ongoing sap-sucking insect problem that needs fixing at the source.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
Is sooty mould itself dangerous to my mango tree, or is it just the black colour?
The mould itself mostly just sits on the surface and does not rot the leaf or fruit underneath — its main direct harm is blocking sunlight from the leaf, which weakens the tree a little in a heavy, repeated attack, and making fruit look dirty and unsellable. The insect producing the honeydew underneath it is usually doing more real damage than the mould itself.
I sprayed a fungicide on the black coating but it keeps coming back — why?
A fungicide sprayed on the mould does not fix the real problem, because the mould keeps regrowing as long as the sap-sucking insect (hopper, scale or mealybug) keeps producing fresh honeydew. Control the insect with the right insecticide at the right stage, and the mould will stop being fed and weather off on its own.
How do I get rid of the black coating once the insect is controlled?
You usually do not need to do anything extra — once the honeydew supply stops because the insect is controlled, the old sooty mould gradually dries, flakes and washes off in rain over the following weeks. A strong jet of water on reachable branches can speed this up a little, but it is cosmetic, not a required treatment.
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.