My willow tree is not growing very well it has a greenish mould or moss type thing have added a picture to help.
1 Answers
The mould or moss-like growth is lichen and is not any harm whatsoever but grows when a plant has not got a proper leaf canopy to cast shade. The canopy is scant because of willow canker disease.
This is not treatable in practical terms and if the tree is too badly affected it will need to be removed. Some willows are especially prone to this problem.
More at: https://gardenie.wpengine.com/gerrycategory/willow-canker/?id=5707