Fireweed, mildew on deciduous azaleas is almost a given in our area. Since it rarely causes lasting harm and is more of a cosmetic issue, I take more of a passive acceptance approach :) If recurring and severe, chances are the shrub needs a more open, sunny area but in my coastal site (humidity), even that is no guarantee.

The problem with the all in one products is you are applying two chemicals not needed that don't address your problem, an insecticide and a fertilizer. If that product is granular, you have the issue of it needing to be 'scratched' into the soil, not recommended for azaleas with fine surface roots.

Recommended are : "Chemical control: Begin multiple applications when you first notice the disease on current-year leaves. Early detection aids overall control.
Bayer Advanced Disease Control at 0.75 fl oz/gal water.

Bayleton(Landscape only, not for use on plants for sale).

Bicarbonate-based products. Might supplement a normal program when powdery mildew is first observed.Thorough coverage is essential.

Ortho RosePride Funginex at 1 Tbsp/gal water. Thoroughly cover both leaf surfaces."

Or, you could also do nothing at all :)

In the early stages, rinses with plain water can prevent infection.