^Some strains are very sensitive to nitrogen overdose during flowering, while others are not. I'm guessing that if the problem wasn't a light leak or excessive temps, it was too much nitrogen. It can revert budding energy into energy directed at producing new foliage, stalling bud-development. I did it recently, and it drooped yield from 2 ozs per plant, to about 20 grams per plant. The buds never put on any density. IMO, it's way better to have them yellow early, rather than be too green(excessive n). I've had plants that yellowed waaay early, and still produced some great smoke. Doesn't work that other way around.
Also, it could happen if you trimmed a bunch of fan leaves. That'll kill a harvest quick, of you get carried away with the trimming. My buddy just found out the hard way. I gave him some of my extra clones a couple months ago(his first grow), so his and mine, were all the same age. He vegged his for 3 weeks longer than I did. I finally got to see his last night, 7 weeks into flowering(8 week strain), and he was expecting me to be really impressed. They looked decent for a first attempt, although somewhere airy and small, but nowhere near what mine were. Then, I brough him to my house, to see mine, which are ready for chopping. He almost shit. Mine are twice as big, and have 6x as much bud on them. He wouldn't listen to me to not touch the fan leaves, but noooooo.....he read about it in High Times, and thought I was talking out of my ass. That, was until he saw it with his own eyes. Let me tell ya, he'll never touch his fan leaves again.lol
