As it now stands, you can apply reaper poison to your weapon, but it’s gone after one hit. To reapply, you need to go back into your inventory and drag another bottle to your weapon. Needless to say, this is quite inconvenient in the middle of a fight. So, as it stands, reaper poison is of little value.
I suggest that reaper poison act like arrows. With arrows, you apply one to your bow and as long as you have arrows in your inventory you can keep shooting. It would make reaper poison a worthwhile buff if it acted in the same way; apply it once to your weapon and as long as you have some in inventory it will automatically be applied to your weapon until you run out.