This is one I got in bud a little over a month ago. I have struggled with it a bit, it got stem rot (I think from me watering in the evening). I poured alcohol down the stem a few times and on the black spot. I thought I got it then I started having leaves yellow from the stem and fall off and lost 3 more!!
Well I finally got it the last bout, I poured alcohol down the stem cut off any yellowing leaves at the stem and placed cinnamon on all the wounds. I still have 3 leaves left and they are nice and green. The black spot has completely dried out now. Throughout all this my buds are opening!