Another of the fungi diseases, rust has other things in common with Blackspot. The causes and preventative measures are also similar.
Rust is more common in cooler damper climates. Here in my corner of North West Victoria, Australia, it is virtually non existant. Our summer is VERY hot, most days are well in excess of 30c with many days of 40 and higher, and humidity is generally low. Rust isn’t an issue.
However, I have lived in climates where this thrived, and was a never ending problem over a cool wet summer.
As with most rose diseases, prevention starts with having healthy plants. That means well fed, well watered, 5-6hrs a day of direct sunlight, and good air ciriculation.
The treatment for rust is more preventative rather than curative. Rust will often start on the lower more mature leaves first and work upwards, so keep an eye on these. Pick off infected leaves and do not compost them. Either bin or burn them. The milk treatment for blackspot might also help, but this will not stop rust, rather it will make it more difficult for spores to get started.