Some of my echinaceas have gone to seed. But I notice that when I cut off the conehead, there is white stuff at the base. Sometimes I find it on the stem as well. I looked at the plants, but it's really not on any of the leaves. Could this still be powdery mildew? In my zone it's hot and humid and the plants are in full sun most of the day.

It would help a lot if you could post some photos Deborah.

Deborah, I agree ... if you can post a photo or two showing the white stuff at the base of the flower head it might be easily identified. Meanwhile, here's a link to images of powdery mildew: https://www.google.com/search?... Most images show the mildew on the foliage but if you sroll down the page a bit there are some roses or other flowers with mildew at the flowers.

And, in case it's mealybugs, here's are links with photo's for those critters:

http://gardeningnaturallywithc...

http://www.organicgardening.co...