If you can't find SM-90 at your local hydro store, I know you can get it on Amazon and Ebay. From what I can discern from the rather sparse info about this product, it would be possible to spray this on your plants about halfway through flowering in order to PREVENT bud rot from showing up right before you harvest. It may even help prevent rot from occurring while you are drying your harvested buds. The smell of the coriander oil (pressed from cilantro seeds) is supposedly detested by spider mites, so it would also help keep the mites away from your girls in flower.
Or that is my hope...