Powdery mildew is most often stimulated by a discrepancy in humidity compared to soil moisture. Warm, damp air (high dew point) and dry soils. Lack of good air circulation is also a contributor. The pathogen is actually sensitive to water (rain, irrigation), which will kill off the spores.

You can look for Shortwood or David's Lavender. They are both sports or hybrids of David. Shortwood is a medium pink with lighter eye and David's Lavender is a medium lavender. Both are tall like David and quite mildew-resistant (at least in my garden). Three others I can recommend are Robert Poore, (darker, almost magenta-pink,) Mrs. Pepper, (medium pink with white eye,) and Katherine, (light blue-lavender). If you are looking for a color you can see across the garden, I would suggest Robert Poore. Here is a link that might be useful: phlox 'Robert Poore'

Hi all you people covered with white powdery stuff.... I have been battling with powdery mildew for years in a very mixed perennial garden...and so far haven't used anything but have done a lot of reading and observing. First: DO NOT water late in the evening and avoid overhead watering IF you can....You can see the overnight results sometimes from mid summer on if you water late in the day...hard to avoid sometimes, I know. The plants must dry quickly to avoid becoming infected. Good ventilation makes all the difference for SOME plants but there are others that are famous for being susceptible to powdery mildew no matter what you do. Still others seem pretty much immune and many fall in between. Summer Phlox is the most famous of all for attracting powdery mildew. I only buy Summer Phlox that say they are resistant. The White Davidii, as someone mentioned is a wonderful phlox that blooms early and strong and has never been a problem in my yard. Two others also stay clear of it. One that I thought was supposed to be resistant had some powerdery mildew this year (Nicky-a purple) and also didn't flower. Powdery mildew not only looks crumby but has a big effect on the flowering and vigour of SOME plants....(Some others seem to tolerate it.) Another plant that I can count on having the dreaded PM is fall aster. Thinning early in the season and keeping it well watered helps to keep it from getting severe-- but get it is does. Never seems to effect the flowering of these though. But of course this is blown in the wind, tracked on the feet (look out grass!) and can spread easily around to other things. Monarda is another perennial that has a reputation for susceptibility amongst the older varieties. In fact, I yanked a red one out all together because of that. As with the summer phlox, there are now good Monardas that are resistant. I now have a large purple one that has remained absolutely free of this fungus and isn't as rampant growing as some of the older ones either.. If you are under the impression that high humidity and moisture will increase powdery mildew....I don't think so. I find that I rarely have a problem in well watered, cool areas. But often do in extra dry areas. ...well ventilated or not. And I am located in the semi-desert area of the North Okanagan of B.C. Personally, I will not use any of the commercial stuff that is recommended so casually in older books for controlling everything under the sun. The only thing I might try IF I was desperate would be something I first saw recommended by Rodale's Chemical Free Yard and Garden (publisher of Organic Garden Magazine). A mixture of baking soda and water with a tiny bit of cooking oil added to help make it stick. I expect that works as I have great faith in Rodale's research, but like I said haven't actually got around to doing that. It is recommended that you spray this on AS SOON AS YOU SEE IT DEVELOPING as it is more effective to catch it early. You might need to repeat after a good rain.

It sure has been humid lately! I saw a faint white cast on my hostas a while back and sprayed all the mildew-prone plants once or twice already. I mix milk, water, AND baking soda, along with a sticking agent such as a little dishsoap or garlic oil (might as well zap some aphids at the same time). Since my last spraying, everything is maintaining well -- shiny and green here....after tonight's rain, I'll probably be out spraying this weekend. And the mosquitos are out! Rats! But I'm sure someone will give that topic its own thread.