Brown Buds?

Does anyone know why my buds turn brown? At harvest the buds are a nice green color, but after a month they start to brown from the bottom branches first and eventually turns all the buds brown. I think it may be a disease but I am not sure what is the cause and if I can do anything to prevent this from happening. It happens with about half the strains that I grow so I suspect it is a disease. Any help or advice would be greatly appreciated.

Can anyone give me some advice regarding my problems of having my buds turn brown after harvesting?

Are you drying them good enough?
That use to happen to me. My buds will turn brown in the cure then I figured out that I wasn't drying enough. I start to let them hang another day or so now they stay green. Try you'll see