I spray for bugs when they appear. (roughly 3 times a year)
I also use a product that has good fungus in it and eats the bad fungus. I have used this for the last 12 months and haven't had fungus problems since. Still get bacteria though.
If you continually use fungicide the fungus builds up an immunity and it will not be effective. You will have to continually rotate it and are only cause yourself potential harm to exposure.