I don't worry about mildew, but I do worry about cedar apple rust (called cedar service berry rust on Amelanchier). The Einsteins who planted this shrub before we moved here sited it directly under a mature red cedar tree, which we can't remove without exposing a lovely fern/hosta garden to the blazing sun. The cedar apple rust galls literally drip onto the serviceberry every spring, and I spend quite a bit of time spraying copper fungicide and picking up diseased foliage.

If you have red cedars within a mile or two, your Amelancier arboreas will be exposed to the spores, so keep them sprayed.

Also, when they bloom in the springtime, don't blink or you'll miss the show! Their bloom time is notoriously short. Ours lasts about two or three days, tops.

Saw your post and thought that I would respond.

If you link to the site below, you'll find general and specific information on the "Downey Serviceberry" and once you arrive at the time and scroll down a bit, you'll find a link to its various "problems."

I will be planting one of these shrubs/trees in our back yard this fall - haven't had the time to finally "site" it as yet, but will do shortly. It has been spending it's first summer in a large pot. Hopefully, I'll be able to shape or trim it into a small single trunk tree.

In addition to this superb web site at the Missouri Botanical Garden in St. Louis, you might explore the Morton Arboretum - Lisle, IL web site, who's "address" is just given below.

http://www.mortonarb.org/

If you scroll down a bit, you'll see a link to their "Tree and Shrub Selecton Guide" which contains some useful information on a few Amelanchier varieties - but not on the Amelanchier arborea - as well as extensive information within their "Plant Health Care" report.

Also buried within their "Tree and Shrub Selection Guide" is a link to the "Sterling Morton Library" which is beautiful and has an extensive collection of books on horticulture,etc. Buried within this library site, is a link to email questions to the reference librarians who work there.

If you haven't visited either place, I encourage you to do so, but plan for a day and a half visit at minimum to more fully enjoy the garden or arboretum.

I much prefer the resources at the Missouri Botanical Garden - mostly because of their "search" engine, better arrangement of the web page, the information, clearer photographs, the links provided, etc., but the Morton Arboretum is also a very excellent resource as well.

Hope this additional information and resources is most helpful.

Bill