Serenade will be a preventative not a cure, I start spraying about half way through my season and hit them once every two weeks, other wise I would lose my Toms to late blight every year, In So maine its turned extremely bad, I literally do not know anyone growing toms in my county without a fungicide at the moment.

As mentioned all fungicides are preventative, not cures so when to start spraying depends on the disease you are preventing and the plant in question.

If talking about tomatoes then spraying from the day of plant out is the standard recommendation because of the correlation between spring's cool, damp weather and some of the common diseases.

Disinfecting cages is your choice. Few do it AFAIK because I can't think of anything off-hand that can over-winter on them.

Dave

Few years ago I also used a home made formula, that I got here at GW. I don't remember exact prportions but it is made withmilk, water and baking powder. I used it on cukes, gourds, squash, as preventive. It worked fine.

I have also used neem (?) oil. Again, I used it regularly to preven fungus desease on cucorbitacea family only.