When the sugar leavs look like that, good chance you got an infection underneath.
open up the bud.. white or grey fuzz along the stem? might have a bad smell too, but may be very faint smell.
leaves can die for different reasons, but any hint of infection, definitely throw it out. there may be non-infected parts of plant, but i'd still be skeptical of anything off this plant. shit spreads before we can see it, so you could still have spores elsewhere and not be able to recognize with your eyes.
if this is indoor, it's 100% about climate control... outside you are left to the whims of mother nature.