I planted a mango tree bought from a nursery 8 month ago and after a while the tip of the tree started changing the colour from green to black and I 've noticed a whittish thick liquid around the growing tip. Then the leaves started changing the colour to brown and then they become crispy. I sprayed the tree with a sulphate but so far no result. I attached some pictures just to have a look. Could you please help me to save the tree.