I had that happen for the first time this year. Humidity is low in my home summer, A/C and winter, furnace.
We had 2/3 weeks this year in between of 90-100% raining every day. I had a strain of very, very dense bud at finish.
This was also my first time growing in the summer and the last 
brò there are no spores, it is not botrytis it is just a bit of rot, if it had been botrytis it would have already infected all the plants!
My question is, how can you be sure it hasn’t infested every plant?
Botrytis IS bud rot.
lol…have it your way, bro 
yes, but it is not a real rot, a very small penetration of moisture stopped in time!
you will see that they will all be healthy, it is not the first time that this has happened to me.
Why create a thread asking if it’s mold then when people state what the problem is and the best way to fix you won’t accept the answers. Pretty much pointless even making the thread 
I wrote “could it be mold?” and I accepted the advice and in fact I cut that moldy part, but I don’t think it is Botrytis, in my opinion it is a small penetration of moisture blocked in time, botrytis is different.
That is bud rot. There are definitely spores flying around your entire grow space. Cover any parts that are visibly infected, with a plastic bag and cut down carefully so as to not spread spore. Then consider cutting the plants early I had this last year and had to chuck everything after inspection with a 60x loupe. It’s hard to see with the naked eye but it’s gonna be all over the place.
For your next grow try and keep the extraction and circulation fans on at all times (unless you have a controller operating them). I would also consider more defoliation as a way to allow for air flow. This will help dramatically for your next run 
I’m with you on that once a plant has some rot it’s time to bin it never mind trimming the bad parts off lol…one of my first grows I got bud rot I didn’t really know a lot about it took off the buds with the rot ,harvest the plant have it drying in paper bags check the bag 3 days later plant was wearing a white mold coat lol
And now I just been the plant
Any sort of
Mold is terrible after bringing a plant up from seed then you get mold or rot like I said I just binned a plant other day was ready to harvest as well,cut the 2 buds off and wiped the mean stem with peroxide,checked the next day mold was growing back in the same spot so fux that