"Do we know if any treatments have been tried? And do they indicate even a LITTLE improvement?"
There was a study published in the AHS Daylily Journal several years ago (Summer 2010) that seemed to show some ss reduction with an insecticide and also with a fungicide (separately as far as I recall). But it did not prevent spring sickness completely.
Removing scapes does not seem to be a factor. What does seem to be a factor is that affected fans were not new ones in the current season. So you may see an apparent association with fans that had produced scapes the year before.
A lot of questions are answered on the spring sickness task force FAQ page:
http://web.ncf.ca/ah748/qanda....
as well as on the experiments page link I posted above, here it is again:
http://web.ncf.ca/ah748/2002.h...
