Powdery Mildew -- Early stages, budding plant

I’m finding all sorts of good info on controlling Powdery Mildew, but very little specific to plants that are just into their budding, like this one:

Right now the PM is barely visible on the leaves, so I seem to have caught it early, but it won’t show up in this pic (trust me, it’s there).

Are the buds too far along to spray with this commercial product?
Sulphur 0.40% It’s a garden fungicide safe for vegetables up to one day before harvest

If this is not safe for the plant pictured above, what would be?

Also, how should I deal with the grow-box once this plant is harvested?

Thanks in advance.

I think that’s okay, in that phase. It’s not too far along.
If this is an indoor grow, increase air flow and exchange.

Thanks. That consumer spray is available almost everywhere.

So I guess an infestation of the box is unlikely?