My guess would be some sort of chemical damage....but I don't think it was herbicide......by chance, you didn't use any "soap" solutions in the vicinity, did you ? Maybe washing the siding of the house ? The fact that the lilies are showing some of the same damage makes me doubt it is any sort of frost damage. Another thing that I would do, is dig one of the affected plants, and examine the roots. IMHO, whatever is affecting them is "root related".
