If your bonsai tree is turning brown, here's what you can do:
1. Water the tree more often if leaves are falling off.
2. Transfer your bonsai to a well-drained pot and trim withering roots.
3. Apply rubbing alcohol to molding leaves and spray with pesticide to remove insects.
4. Remove any dead foliage using sharp pruning shears.
5. Water the soil properly and cover the pot and plant with a polythene bag.