Fungus - BL Ports of Paradise

[Clawhammer]

I found some yellow spots on the front of 2 of my Blc Ports of Paradise's older leaves. Turned them over and there were little white spots on the underside where the yellowing was. Other leaves do not have either yellowing on top or little white spots on the bottom.

I am guessing fungus and thinking a systematic like daconil. Let me know your thoughts and any experience with this. Should I treat all catts in my collection?

Thanks everyone.