Just to elaborate on what Lorn said, botrytis infections almost always occur on the plant above the soil. Treating the soil to reduce inocula (inoculum) is very helpful, but does not replace application of a fungicide on the plant itself. Because Captan and copper fungicides are contact pesticides, they work best as a preventative, and may not be completely effective once the disease is manifested.
I don't have the botrytis problems that many people do (even here where I live). So I don't have much experience combating it. All of my beds are mulched all year, though, and that's an easy environmentally safe step you should practice (even in pots).
