I did a search and found some comments that some folks have had problems with mildew and leaf diseases - these problems seemed to be associated with times of the year when high heat and humidity were issues (by the way, most people reported that they had no problems growing Scabiosa).

We have been having hot weather and the plants do receive overhead water from irrigation, so I imagine we could be seeing problems associated with same. Really a nice plant when it is doing well, so we would enjoy finding out what we is doin' wrong. Thanks in advance if anyone has any suggestions. Chris

Description:
These prolific plants bloom early and heavy, and continue on a lesser degree if the spent flowers are cut. The flowers are long stemmed. The foliage is neat, forming a low mound of decorative leaves. Divide clump in spring every few years to rejuvenate the plant.

Common Name: Pincushion Flower
Botanical Name: Scabiosa
Type: Perennial
Soil Preference: Prefers a well-drained, alkaline soil. Can tolerate some drought and will grow in dry to moist soils.
Light Requirements: Full Sun to light shade
Attributes: Attracts birds & butterflies, Deer resistant, Extended bloom season; Provides a source of nectar for bees and butterflies.
Pests: Spider mites, slugs, vine weevil
Diseases: Stem rot, mildew, leaf spot, anthracnose.
Good Companion Plants: Bellflower, Daylily, Hardy Geranium, Lady's Mantle, Pinks
Care: Divide clump in spring every few years to rejuvenate the plant. In spring, cut back to basal foliage. Dead-head spent flowers after blooming. Will not tolerate hot & humid conditions.

I don’t know if you’re having the same problem as I had, but last year I gave up on growing scabiosa. I love the flowers and the fact that it blooms for so long, but mine was always covered with mildew. When I moved in here I had a blue one, and for two or three years I fought the mildew. The plant almost always looked bad and just kept going downhill as the summer went on. The year before last I threw out the blue one and bought a brand new pink one. I planted it in a different place to keep it away from the mildew infected area—but it didn’t work! Within a couple months it, too, was covered with mildew! I kept it till the following spring to see what it would do, but nothing helped much with the mildew and I finally threw that one out too.

Based on personal experience, I have a different theory about mildew, though nothing seemed to help with the scabiosa. From all the things I’ve tried, keeping plants well watered and healthy is the best way to prevent mildew. Except for the scabiosa, the only time I’ve had a problem with mildew is when I’m under watering things and they’re stressed. Watering overhead and temperature don’t seem to make any difference when I keep the plants well watered. It even seems to help with things like zucchini—at least for most of the summer! Since I’ve been making sure things—especially mildew susceptible things—are kept adequately watered, I haven’t had any mildew on my roses, upright garden phlox (one plant!), or Thalictrum. The first few years I lived here they were all covered with mildew by mid summer.

My scabiosa was growing right at the bottom of my deck steps where I constantly go down to get into the backyard, and I wanted something there that would bloom a long time, so I decided to replace it with a Catananche, Cupid’s Dart. That was something I had always wanted anyway, and tho both the foliage and the flowers are very different from scabiosa, it blooms for a LONG time, and the flowers are way cool too. Mine was tiny last year, but is big and doing beautifully this year, and I’ve taken pictures, but they’re still in the camera! Here’s a link to a pic I found online. The flowers are about an inch in diameter, and sit 14-16' above the narrow foliage on wiry stems. I planted the Catananche in the same place where the original mildew-infested scabiosa was, and I haven’t had any problem with mildew on the Cupid’s Dart or anything else in that area since I took out the scabiosa. If I ever figure out how to grow it without mildew, I’d love to have another one—or 10—scabiosa again.

If you want something more similar to the scabiosa, Stoke’s Aster, Stokesia laevis has the most similar flower in size and form. I want one of those some day too, but haven’t gotten around to it yet. Don’t know if they’re susceptible to mildew, but I don’t remember any problem with it when I was selling them.

Wish I had some happier information for you, but when I’m growing flowers, it’s to enjoy them, and when I’m constantly fighting with them, I’m not enjoying them very much!

Good luck with yours,
Skybird

Oops,
Skybird

I've never had one mildew. I water a lot because the daylilies love water. I water overhead which is supposed to be a good way to get powdery mildew.

Skybird, I love Stokesia, but they're not reliably hardy for me.
Karen