I've had my first Chinese elm for over a year now; it recently had a battle with spidermites and was seemed to be recovering from them well. However, I recently noticed the trunk was green in certain places and that growth was patchy and not in certain areas. There also appears to be small black spots on the trunk. I've tried experimenting with different watering timings and amounts but it doesn't seem to change anything. What should I do?
Many thanks.