I think it could be the weather.I'm in central Illinois also.It's been unusually dry and after just looking at my rattlesnake masters,they don't look so great this year either. I know they are drought tolerant,but we didn't have the wet spring we usually have.

I lost a load of these, planting in late spring (In my unirrigated clearing). Whilst they might be drought tolerant, it's only when they have got their roots well anchored and spread. The eryngoes are tough, tough plants though - a good watering and they should be fine.

It's the weather.I've had mine in the ground for at least 5 years and they look worse than yours.Does'nt seem like they are going to bloom this year, and they have bloomed great in previous years.