I have a potted green leaf Acer in my garden. It's about 5 feet tall in a large pot. I have it about 3 years. This year, it got a white fungal growth around the base. In the last week, one large branch has rotted. It is not broken and there is no obvious reason why it died. Does anyone know what the fungal growth (tiny white fungus) might be and if I can save my tree (which I really love and hate to lose). I have a second Acer in my garden in a raised bed, it is perfectly healthy.