looks like Bud Rot/Botrytis, it spreads fast and typically starts in areas with high moisture, humidity, and poor airflow through the branches and leaves, it is most often caused by wounds in the plant, though it can also form without wounds, often on colas during flowering. bugs, trimming, and defoliation can allow Botrytis to form. A rainy day, or a few rainy days can certainly be the cause of Botrytis if its outdoors. I would recommend going through your plant and removing any areas with that grey coloration, otherwise it will likely spread. I had a crop die from poor maintainence, more specifically poor defoliation, and a humid environment, which lead to Botrytis rot. Happens to all of us, just gotta keep on keepin on, looking pretty good otherwise!