Yes - powdery mildew moves in when plants are stressed out - usually by lack of water. Hanging petunia baskets often need water every day - sometimes when it is hot even twice a day. You are correct in that getting the foliage wet also contributes to the spread of this fungus among us as does watering at night. The best time to water is midmorning so the sun can dry any spores that may splash. I think both million bells and ivy geraniums are mildew resistant. I also agree that pulling out the infected plants is the only practical thing to do for annuals and veggies. It is just not worth spraying a fungicide as by the time you see the mildew it is usually too late for a spray to work. Don't give up - I see beautiful hanging baskets in your future. Keep growing, Marianne Binetti