Could someone please help identify what is wrong with my tree - I've noticed what seems to be some sort of disease travelling up the trunk of my acer palmatum 'Koto No Ito' - I absolutely adore this tree and I've had it a few years now so I'm really devastated to think it could have a disease and might die! I've no idea what could be wrong, I've tried to frantically google but couldn't find anything helpful. I apologise if this isn't the right place for this. I feel awful because I've had such a busy year I've been quite neglectful of my plants other than watering and a quick glance at foliage for pests. Tree seems otherwise fine - lovely leaves, strong growth this year. If it makes a difference this is a potted acer. It is watered but never fertilised. I add bark chips on top every winter. Thank you so much in advance.