All good ideas. Keep in mind botrytis is a type of fungus that is ever present to some degree in the soil. It plays natural part of the decomposition cycle. It's spores can be airborne as well. So when watering your plants, a couple things happen. First, soil is easily splashed onto the lower leaves, both from manual watering or by rain. Second, tiny gas bubbles that form and accumulate in the soil contain botrytis spores that are released into the air in the presence of water. There's a certain smell after a rain or after watering called 'petrichlor'. When you smell that, be prepared to spray the entire plant with a copper base fungicide.
It is best to always be as proactive as possible. Starting now this Fall, do a respectable clean up of old dead stems; nothing extraordinary, just respectable. When Spring comes and just before the noses poke up, spray the garden soil or pots and soil with a good copper base fungicide (or a little Captan worked lightly into the potted surface). This will keep the botrytis population down for a few weeks and keep your risk to a minimum. However, as soon as warm, humid weather arrives, spray the entire plant with a weak solution every two weeks or after a rain. Stop any spraying when buds are about to open and while blooming, then resume when done blooming. To avoid the rain splashing soil onto the plants, cover the soil with a good layer of coarse mulch. The way to combat dew is to have a fungicide already applied. I know exactly what you're talking about. The theory is that the burning rays of sunshine are magnified or made more intense by the dew droplet, thereby making many tiny injuries to the top surface of the leaf where botrytis can get a start. Having a light application of fungicide will prevent botrytis from setting in on those tiny damaged areas. And last, make sure your plants aren't too crowded--keep a reasonable space between them for good air flow.
