There could be several reasons why a young mango tree would lose its new leaves. Below we list the most common possibilities:

• Stress caused from transplanting a tree to the ground or to a bigger container
• Overwatering: Mango trees do not like to be waterlogged. Overwatering can cause the roots to rot, which can lead to leaf drop.
• Underwatering: On the other hand, if the tree is not getting enough water, it may drop its leaves to conserve moisture.
• Environmental stress: Mango trees are sensitive to environmental stress, such as temperature changes, wind, and humidity. Sudden changes in the environment can cause the tree to drop its leaves.

Lack of exposure to sun light for several days, may cause your young mango tree to lose its leaves also.

• Pests or disease: Insects or diseases can cause damage to the leaves, making them drop prematurely.
• Nutrient deficiencies: Mango trees need a balanced supply of nutrients to thrive. If the tree is lacking in any essential nutrients, it may drop its leaves.

If you suspect any of these factors are causing your mango tree to lose its new leaves, you may want to consult with a local horticulturist or agricultural extension office for advice on how to address the issue.