"systemic" (absorbed) vs. "foliar" or "contact-kill" (must contact the target to work).
the systemic is more dangerous to the smoker. i hear from kevin jodrey that you should clone & reclone after using a systemic or it will be in the bud.
(natural nicotine from tobacco being preferable vs. man-made/synthetic, IMO).
edit: I keep seeing this "BACONY BLUEBERRY PROBLEM" mmmmm