Hey VT I hate to be the bearer of bad news but you have some bud rot. You definitely need to cut that bud off asap. Bud rot loves cool temperatures and high humidity. You want to keep your temp around 80f and your humidity around 40% to stop this from happening in the future. Also oscillating fans keeping the air moving and an extractor fan are key to keeping bud rot away. I am not sure if you can do any of these things on your greenhouse, but hope this gets you headed in the right direction.