Powdery mildew is very stubborn and if conditions are right and the rose is prone to it, then that makes it very hard to keep under control. If you are using Funginex, then there should be two types of strengths. The higher concentrate can be used every 7 days. Might be a wisdom to keep an eye on the roses after the rainy season as they may start up again.

Powdery Mildew, most common, is a fungus and is carried on the wind. It can stay on the ground and be splashed onto the bush.
What can you do?
Don't water at night. If you get the foliage wet, make sure it has time to dry.
Give your bushes adequate ventilation by pruning so the center stays pretty clear for air to circulate.
Depending on the weather and where you live, spraying might be the only answer.
ck at your local garden center. I like systemic, because it lasts longer
Spray the underside of the leaves from the bottom to the top then give the top a shot.
I like to spray the area around the bush.
Good luck

Your roses have downy mildew and should be sprayed with a fubgicide or the mildew will kill the new growth. Just ask for a rose fungicide and then following the directions on the package. It won't take long to cure this problem.