Sometimes getting bud rot can be a blessing with plants that are taking a long time (not that this one did), because if you aren't going to treat it, it kind of takes the decision of when to harvest away from you - when I used to see bud rot taking hold I would just chop it.
I've seen a good bit of bud rot this season on various plants, some just hidden on a single cola like above. I really think it can't be fully avoided, just minimised.
I've been using a tea made with Horsetail I picked locally for the past week or so and it really is helping, I've also added a bit of organic liquid cold pressed seaweed to the tea, so spraying it as a foilar feed. I believe if you start spraying it as a maintenance dose early on in flowering it will almost prevent it from even starting, it is also very rich in sillica so really helps the plant grow strong buds, etc.
Look it up, sometimes there's an easy organic sollution just hiding nearby.
Good luck, and those buds look just so tasty, I hope it's as enjoyable to smoke as it is to look at.
Peace