I have a mix of autoflower strains (white widow, ak47 and bubble gum). Outdoor grow. Some new growth (bud sites?) shows black in the leaves. None of the plants have this at all bud sites. One has this in 50% of them, most have 20% and a few have none. It does not rub off, it appears to be pigment in the leaves.
I have seen more then a few pics here with same thing including mine. I am voting for genetics every one can not have the same issues blamed on over watering and root rot. Mine are absolutely not over watered or over fed. Check out the other posts. Different stains, growing mediums, inside outside, all with similar observations.
What’s the common factor? My girls are feminized Super Skunk from ILGM.