My mango fruits are dropping early at marble size, what is the reason (aam)?

Some fruit drop after set is natural, but heavy drop at pea to marble stage usually has more than one cause. The most common reasons are moisture stress and irregular irrigation, lack of nutrients, hormonal imbalance, poor pollination, and pest or disease pressure such as hopper, fruit borer or anthracnose. Sudden hot dry winds and big swings in soil moisture make it worse. First fix the basics: keep soil moisture even with light frequent irrigation rather than long dry spells followed by flooding, and mulch the basin to hold moisture. Make sure the tree is not short of potassium and micronutrients, based on a soil or leaf test from your KVK. Control any hopper or anthracnose that is present, since both cause drop. Some growers use a recommended planned spray such as a low dose of a plant growth regulator like NAA at the proper stage to reduce drop, but the dose and timing must come from your horticulture department because wrong use can backfire. Please show a photo of the dropped fruit to your KVK so they can rule out borer or disease, and confirm the cause before acting. Mind residue and pre-harvest interval for any spray on a bearing tree.