Posted: 28/09/2016 at 13:35
The spores are produced when the knobbly pustules are produced underneath the orange spots. One reason for removing leaves which show rust spots is to prevent the spore producing organs from forming, lessening the amount of spores produced to go on and infect junipers. For that reason I would still recommend removing affected leaves as soon as you see them. However, if that means removing most of the leaves from the tree I agree it may do more harm than good. I have had some success in cutting the affected part of each leaf away with scissors on young trees so as much leaf area as possible is preserved. Of course, if the spot is near the base of the leaf then the whole leaf is removed.
In the case of large trees, all you can really do is sweep up and burn fallen leaves.