Yes, the OxiDate can be applied during flower - I have used it right up until the day I harvest. It is a foliar spray, non-systemic, and evaporates away cleanly without leaving behind any reside or trace chemicals. Its original application was actually in the restaurant business for sterilizing dishware and equipment. Since it leaves behind no residues, you can dunk say, a glass or a pot in it, and then just let it dry, without having to waste time or water on another rinse like you do with soaps. It does not last very long however, you need to re-apply every three days if you are having serious issues. Usually I just use it for spot spraying unless I get a plant that is really starting to have mold issues. It stinks like shit though and will agitate your skin so be careful when using it. Stops mold in dead in its tracks though.