steve, lack of rain is the cause. The rain actually washed the mildew spores off the leaves. Are you overhead watering or using soaker hoses? You can try washing off the leaves of some of the plants.

Earlier this year I had a lot of PM on my roses and other plants, despite the roses being sprayed with fungicide. Sometimes you can't beat it. It has subsided substantially since it has been raining regularly here.

There is a product called Wilt Pruf that you can spray on plants that is supposed to help keep the PM off.

Luckily PM usually doesn't do a lot of damage, it just looks bad.

Some planting areas are spray irrigated and beds near the house are soaker hosed. I'll look into Wilt Pruf and keep up my Neem and Bayer assault. Something, likely fungal, has nearly killed 4-5 euphorbia Blackbirds.
Thanks for the input.