Since the fungus can overwinter in plant debris, you DO want to start spraying as early as possible (with prior rust experience) and in 7-10 day increments, weather depending. Any fungicides registered to control rust are only preventative so you need to start spraying before any signs of the disease appear.

The other critical element is to offer the best possible cultural conditions - plenty of sun, good air circulation, any necessary irrigation and nutrient supplementation and most importantly, good garden sanitation. Get rid of and destroy all affected plant material and mulch the soil well over winter.