It looks like you could have a root problem. Carefully pull one out of the pot and feel around for roots. If growing right it should be a big wad of roots. Sometimes caused by overwatering. You need very good drainage for MJ roots. They need oxygen at the roots to grow good. You might try some root growth hormones, but I would check the overwatering issue first.
killerweed420 Reviewed by killerweed420 on . Is this Mold? What to do? PICS..... Hi all, I'm in very early flower indoors under 1000w HPS, in soil and coco fiber w perilite. temps are 80's and 90's. I feed with 10-30-20 one part nutes. Something is affecting my plants, it starts on the grow tips of the lower branches and works its way up the plant. Affected new growth tips are droopy and turn black or grey and die while still very small, essentially ending most growth of the branch it heads. Also, some leaf stems suddenly wither and shrink to the width of a human hair, Rating: 5