Because of my interest in spring sickness, a few years back a couple of people separately sent me some pictures of damage they thought might be spring sickness. It can happen with spring sickness that the interior of some fans rots but it didn't quite look like ss to me, it looked more like what is being described above. Turned out both had used the same specific brand of surfactant. If you decided you did want, or need, to continue using one, you might test a different brand on a few plants first without the pesticide in it. It's always a good idea to test products you haven't used before on a few plants first before treating the whole lot just to be safe.
I was also sent some other pictures to determine if they were spring sickness, but in that case the damage was from an over-the-top herbicide. The product name was the same as had been used before and was "safe" for daylilies, but the manufacturer had changed the active ingredients in the product and the "new improved" version damaged the daylilies.
BTW I wouldn't use Sevin unless you're sure that the problem is an insect that is susceptible to it because it is one of the insecticides that can increase spider mites.
