@petruske how has your weather been rain-wise? I had some cultivars with SS this year (although nowhere near as many as you). You are right in that at first they all look fine. But when all my dormants (including very lates) have emerged and I start counting fans (typically April) I tend to start seeing it.
The difference this year is that we have had a TON of rain which has caused everything to grow at an insanely rapid pace. When I checked this morning many of the cultivars with SS had already grown out of it. I wouldn't be surprised if they even bloomed this year (typically they don't bloom the year they have SS). The few that hadn't recovered completely still look as though they will recover soon although I do think they won't bloom this year. It seems rapid growth in the Spring is key to having the plants bounce back. I did also fertilize in April so that may have helped also.
We had an incredibly rainy year last year including the winter. Very few long, cold snaps and lots of rain instead of snow. No late hard freezes (or even anything close to a freeze) but I still got SS. We haven't had hardly any sun which I would have thought might make the situation worse but apparently not. Fungal diseases should thrive in this weather but so far all my plants look great.
Why SS occurs is a complete mystery to me. It seems completely random. It can't be weather because each year I have a few plants with SS and the weather patterns are completely different each year (last year the rains started in early summer so the Spring was normal and we did get late freezes). I haven't seen any pests yet, not even an aphid. If it is some kind of pathogen I don't understand how it can bother some fans in a clump and not others.
