Mold, fungus, and other microbes are intrinsic to growing anything outside of aseptic culture. My fungicide: is to give the plants the best environment I am capable of. I invite the natural process involving microorganisms. The only natural processes I take preventative and curative measures with are insect/animal pests such as aphid, spider mites, and nematodes. More often than not it is the physical attack by insects (or an inadvertent human touch) that gives pathogenic microorganisms a chance to infiltrate plant tissues. Sure, some pathogens are sympatric to the plants themselves, only needing the host to be weakened for them to take control, but in my opinion this is the exception for our plants when we grow them in near optimal conditions.
Microorganisms are our friends; for the most part it is they that take care of removing these old dead leaves in the mountains of South Africa. Lazy person that I am, I encourage them to do their work for me too.