Certified GKH Gardening Expert
Ah. They have contracted an infection. Probably bacterial. This is common in zone 7, especially when it is wet for extended periods. Once infected, it can stay dormant in the plant for quite a while.
the best method for control will be a fungicide, since they also help with bacterial infections. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
Another thing that I would do... Mix 1/4 peroxide to 3/4 water and water it in once. Wait until the soil dries out and do it one more time. It really helps refresh the soil.
They also really appreciate being in the shade. Full sun can scorch them. Make sure to keep them protected from full sun. This article will help you to care for the plant: https://www.gardeningknowhow.com/ornamental/bulbs/toad-lily/toad-lily-care.htm