silvasurfa wrote:

Do you think maybe using that Charlie Carp fertiliser would help with the
mildew? I know Burkes Backyard or Gardening Australia did a story on roses
at Flemington racetrack, and apparently since they started using fish
fertiliser as a foliar spray they have been able to stop treating the roses
for black spot so much

That would probably be because they were growing strongly. A healthy
plant is more likely to resist disease, just like a healthy person, and
foliar sprays are a good method of feeding a plant. It would be more
prevention than cure. Seaweed fertiliser would do the same job.

While a good fertiliser won't help the mildew once it's established, it
can certainly help the plant outgrow it! I once had a zucchini planted
in pure mushroom compost grow and provide me with several zucchini each
week for a couple of months despite being convered in powdery mildew!

Tara