Grey mould rife in greenhouse

Hi I haven't visited my greenhouse in a couple of weeks, but I had some Salvias bought as plugs which I had potted on and they were doing well. Today to my dismay I see that botrytis has rampaged through most of them. What is my best course of action, is it worth applying a chemical fungus fighter to try and save them or should I remove and destroy them so as not to infect the other plants? Any advice on how to stop this happening again would also be helpful, the greenhouse has an automatic vent so air does circulate on warm days. Thanks in anticipation of your responses.

Maybe needs even more ventilation if it's been as mild and damp for you as it has for me over the last few weeks. 

Ideal conditions recently-a lot of plants are affected-keep them really dry -remove all infected leaves- increase ventilation and hope for the best

Chemical spray will not help at all really

Thanks for the advice. I'll try those suggestions and hope for the best. Fingers crossed!

A good wash out of soap and water and do not leave water in the greenhouse and ventilation in good weather and get rid of any deceased plants .