Mango Fungal Infection

Scott 10 starts with ...
Hi all,
I have around 10 young mango plants and all of a sudden several of them have developed a fungal infection which has caused them to drop leaves and killed 2 plants. I have been applying Liquid Copper every 3-4 weeks but still happening. Today I sprayed with Yates Mancozeb to see if any improvements.

My Nam Doc Mai died from this and currently have a Banana Mango, Sensation and KP suffering badly.

Does anyone have any ideas?

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