This has been the worst second half of a daylily season I have ever experienced and it continues.
I finally finished a complete round of watering with the hopes that rain was on the way, then the predicted rain turned and went away. So I will probably have to restart another round of watering soon. I takes me about four days to get everything watered in this heat, I can only work till about 10:00 am then I head indoors.
So yesterday and today I have been checking the plants that have been so badly affected by heat dormancy, summer dormancy, or spray misapplication, rot or whatever else it might be causing my problems. Actually after an inspection of all the plants it was not as bad as I had expected, still I wrote down two pages of plants that looked almost dead or dead. With a little further inspection(pulling back the mulch) I did find quite a few that still shows some signs of life.
So being almost afraid to pull of the fans for fear of the just pulling off at root level, I knew I had to do it anyhow. I did find a few that were definitely rot problems, but the great majority did not show rot. But, I came to 'Coit Tower' pulled on a fan and the fan came up out of the ground completely roots and all, I pulled on another fan, the same thing happened. Odd, I thought. So I pulled on the main clump and the entire clump pulled up just as if if were not even planted, no resistance at all. So I just took the clump up to the shed, divided it and planted the fans in a new bed.
I ended up with 16 fans, nice roots on them all, but very little foliage after being cleaned and trimmed, and the fans just pulled apart very easily as if there were no roots entangling them together. It was like the plants had the thick tuber looking roots, but no fine roots.

Then today I ran across the same problem and took photos before planting the little divisions, the plant today was much more deteriorated with even worse looking foliage. This is 'Renegade Lady' these four were in one clump that just lifted right out of the ground with almost no effort. This was potted.

I over exposed the photo so the roots could be clearly seen to show the plant did not have rot.

Both of these plants are at least a year old, and should have been well rooted by now and firmly attached to the surrounding soil.
Any ideas what can cause such a problem?
Many of my other plants are just showing rot, some completely gone, others I might can save. Many look as bad as the ones with rot, but it appears to either be heat or summer dormancy mainly. Then many plants look so bad that I have really considered I must have somehow sprayed them with the wrong mix or with the wrong chemical (I don't know how or when, but the plants look so bad I have to consider that a possibility).

How odd, I have not seen that. You got 16 fans from Coit Tower, so sounds like it has been growing well. Hope you get some answers, I will be following. Not like your problem, but I always have a problem with crown rot. I have/had my best plants in an area that never had crown rot. Last year I lost many plants in that area . Along one side of my sidewalk, but healthy daylilies between. Some newer, but some older nice clumps. Mystified me. Hope you find your answer.

I have lost more plants to crown rot this year than ever before. I hate losing any plant but, it seems rot knows which ones we love the most and are great at selecting them.

Any chance you have a vole problem?

Larry, I am so sorry to hear this. I have one or two that look close to expiring from the heat, and I lost a couple to rot, but nothing like what you are describing. Here's hoping the plants recover and give you a great bloom season next year.

crawgarden,
I do have moles, I do have field mice, so I won't deny that I might have voles, but looking at the roots in the photos and looking at the roots on other plants in my garden I have to conclude that voles are not part of the problem.

Larry, so sorry to hear your daylily season is going so poorly. I have not seen anything like that, either, but first question that comes to mind: is there 'anything' that you have done this year that is different from previous years? (Different fertilizer, different mulch...?)

It seems to be too wide-spread an issue for the problem to be just the specific plants affected; is there anything (other than the weather) that could affect so many? I ask, because several years ago a gardener I know had a problem that turned out to be 'garden wide' and it was caused by the mulch. The mulch had been contaminated by some shredded wood at the recycler ... the wood had been pressure-treated.

Personally, I do not know what is used in pressure-treated wood to prevent rot, but apparently it had a negative effect on the garden!

Oh my goodness Larry, how sad and frustrated you must be. I am so sorry to hear this. I am afraid I don't have a clue what the problem could be, but hope you are able to save them.

Even in this heat, many of the plants that went summer dormant have new little green shoots popping out of the ground. Hoping yours are doing the same, Larry.
The only rot I have found so far was on a potted plant🙏.

Unfortunately, several of our plants seem to have problems like Larry's. I keep hoping they will snap out of it and come back in the spring, and that may happen for some. The one that has really upset me is Fat Tuesday. It started a decline and I feared that it was crown rot, but when dug up and inspected, the roots looked pretty good and it still had one not so bad fan. It was potted and now the fan has disappeared, so we can only wait and see if it will recover.

@adknative,
Unfortunately I do some things in the garden differently every year. Different fertilizers, different soil amendments, different sources for mulch, etc.
But the mention of mulch did seem to be a possible cause at first, this year I had more pine straw than I needed at the time and I made two large piles to use later (so the timing seemed that might be the problem). The decline in my plants like I am seeing now (not the other decline due to the cold and freeze damage which was also different this year than ever) started later maybe early June. That would have been about the time the original pine straw mulch needed to be refreshed using the stored mulch. But then I thought no that can't be the problem because I was having the problem in all of my potted plants also and they did not get any pine straw mulch.
So I am back to thinking that somehow, some way I must have sprayed the plants with something they did not appreciate.

@Seedfork I don't spray with any chemicals in the gardens and am having some of the same problems as you. Plants that looked healthy and were planted with amended soil and light fertilizer have declined. Others have thrived. Some of the potted plants are now declining as well and I'm not sure if they're just going dormant early - and haven't checked to see which are DOR, SE, or EV - or what the problem might be. A few are putting up some small new green shoots. I plan to plant them all out in the new bed within the next two weeks (hopefully the trees really will be gone tomorrow as planned) and keep my fingers crossed for next year. It's been a puzzling year, beginning last Fall.

Any possibility it could be nematodes ?

crawgarden,
Yes, there is the possibility of nematodes. The symptoms above ground would be very similar (almost identical) to what is happening to my plants. There are several different types of nematodes in Alabama, the main one being Root Knot nematodes. Looking at my roots I see no sign of that type of nematodes. It seems it would take some type of lab testing to determine if it were some other type of nematodes. So I guess my plan for that is to just wait and see if the plants improve and if the same situation should arise next year, being even if I knew it was some type of nematodes it would probably mean I would have to dig up all my daylilies and treat the soil in some manner to get rid of them then wait a period of time before ever planting back another daylily.

Wow, that would be drastic measures. Hope you don't have to do that, Larry.

Larry could the extension service help any?

They might be, they have not been much help in the past, but it might be worth it to give them another chance. I will try calling them tomorrow.

Probably about 25% of my Daylilies have struggled this summer. Branching and budcount have been lower for nearly all of them. Thought I lost "Leprechaun Curls" ALL foliage turned brown and dead and I just mentally shrugged and went on. Now as green and big as it ever was! Weeds are rampant d/t an old rotator cuff injury. Had surgery over a decade ago, still flares up if I push it. I'm back to spending an hour each day weeding or culling seedlings. It's the best I can do at this time. So it will have to do. I guess the only advice I can impart would be to take care of you. There is not a Daylily in the world worth heatstroke or worse. They sell them every day. From what I hear, this has been a hard summer all over. I really doubt it's anything you have done.

So I talked with the local extension office today, they did not really know what the problem might be other than environmental issues caused by our weird weather year here. She said she had had many complaints from people saying their plants were dying. Did not seem to think it was a nematode problem, did not seem to think it was a spray issue. Really like most of us, just had no idea other than it has been too cold, too hot, too cool, too dry, too wet, etc.

Well at least you can have some confidence that it's nothing you did that caused problems!