Essential for Botrytis is the climate around flowering. Botrytis does not / hardly have the possibility to infect living, active parts of the plant. If Petals fall, Botrytis does have an excellent start in these dead flowers parts. Falling on leafs, or remaining partly on the still green fruits. From that part Botrytis normally infects the still green fruits. First signs are the reddish colored sepals. After quite some time they become brown (like in the pictures above and below). Later as fruits start coloring to white or later to red, the fruits are totally infected as we know with Botrytis. 

Essential for prevention is a climate not optimum for Botrytis: dry (rain protection), low humidity and a fresh good growing crop (optimum irrigation and fertilization). 
In case of high humidity or rain, fungicides especially around flowering can protect. 
Used fungicides are: Signum, Switch, Teldor, TMTD, etc. 

Important in this case is to change the type of fungicides in order to prevent resistance.