Supplier of Botrytis spores wanted.

If I had to guess, I'd say the spores come in from the field on any grapes you get. It's a matter of providing the right conditions to promote botrytis: IIRC, fog at night that burns mostly off in the morning, followed by days that don't get too hot. Cool coastal areas are right for this. I've heard of sprinkling vines in drier areas to promote botrytis. Gotta be careful with that though. The same organism that produced botrytis also produces bunch rot. (I suspect that's a matter of getting the grapes _too_ wet. The berries need to dry off completely for awhile.)

Tom S