OK thanks I will cut off the dead and Bagget and water the hell out of it thank youBugs (or caterpillars), eating bits off the plants and spreading illnesses.
Some kind of pathogen. Or mold.
Maybe cold air, but I'd expect the damage to be less selective.
I'd also expect more damage if it was nutrient- or pH-related. In other words, on all new growth, on old growth starting at the bottom and progressing upwards, or just the entire plant in general.
If those were mine, I'd be out there with a good magnifying glass, checking all parts of the plants (they move on from dead areas once they've eaten all the useful stuff), checking both sides of all leaves/etc. I'd also bag the dead portions while they're still on the plants (so my actions didn't spread anything) and then cut them off and dispose of them. And probably hose the <BLEEP> out of the plants afterwards, early in the morning so they'd have plenty of time to dry out afterwards.
Could be something has been making a meal of the root systems. I suppose if the damage quickly gets worse and becomes the entire plant, then that'd be a likely possibility.
All of the above is "IMHO," of course. I'm no professional botanist, lol; have just grown a plant or two before. If cannabis is a legal crop in your location, then I suggest bagging/cutting off some of the damaged area and taking it to your local agricultural extension office and asking them - they are professionals, and that's what they're there for.