@Avnsmith, why do you think it is fungus and not temperature problems ? Vietnam has temps in the region of 35- 38 ° C at the moment. Japanese maples will suffer greatly in that heat if not placed in a lot of shade and have enough water at the roots to draw on. Browning at the tips of the leaves is a good sign of this. Also your maple maybe weak from not having its right amount of dormancy during the Winter, hence not strong enough to cope now.
