If it's a 'natural' garden, wouldn't nature rid of it her own way? I say leave it and let it do how nature would if humans weren't around.
They are on the underside of every leaf. So can't remove the leaves. Don't want to use fungicides as it's a wildlife garden and want to keep it as natural as possible. However if it's likely to spread I will have to remove the whole plant I guess. Shame really as the flowers are lovely and it's attracting the 🐝 bees 😟
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
Have a look here and see what you think
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.