For botrytis it works best as control and prevention. If you have budrot cut it out, remove it, destroy it then treat the plants.
And look at each cola that has budrot. If you think its just one bud, probably not. Feel and look above and below from where you remove the rot. The buds that are just starting to rot will be the leaves will be softer and smushy instead of crisp leaves especially near the stem. Lots of times can see the mycelium running alon the stem too. I remove one or two nodes below the last place I see rot and toss with the mush.