In Kirra wrote:
It is only used after
pruning because it will damage any fresh growth (or any leaves) on the
roses.

Actually, Kirra, it can be used any time of the year. Even the Yates
product instructions say that (I've got a bottle myself!). You just use
it at 10 ml per litre of spray instead of 20 ml/L.

I've used it on powdery mildew mid season, to great effect. No foliage
burning problems, but it did make the foliage smell awful. The side
benefit of this was that a rogue possum decided that my roses were now a
bit too spicy for its palate. Awww.