Black sooty mould coating my mango leaves and fruit, what is the reason (aam)?

The black coating is sooty mould, and it is almost always a secondary problem. The most likely cause is a sap-sucking pest, usually mango hopper or sometimes mealybug or scale, feeding on the panicles and tender leaves. These pests excrete a sticky sugary honeydew, the black fungus then grows on that honeydew, which is why you see it on leaves and fruit surfaces. The mould itself does not enter the plant, but it blocks sunlight and dirties the fruit, lowering market grade. Please confirm the actual pest by tapping a panicle over white paper at dawn or sending a clear photo to your KVK or horticulture officer, because the spray decision depends on which pest it is. Manage the pest first, not the mould. Open up the canopy with light pruning for air and light, remove water shoots, and clean badly affected leaves. For hopper or mealybug, KVK-recommended insecticides exist as typical actives such as imidacloprid, thiamethoxam or buprofezin, but you must follow the product label, the pre-harvest interval, and rotate modes of action so resistance does not build. If the fruit is close to harvest or meant for export, check residue and MRL limits before spraying. Once the pest stops, the sooty mould dries up and washes off in the rain over time.