This particular type of cylindrocarpon can affect many different herbaceous type plants, usually around the mid stem area so it's not unique to lilies alone. With lilies, it is less common. There are many types of cylindrocarpons and I do not know exactly which this one this is so I can't recommend a remedy--someone else may know. Other cylindrocarpons do affect lilies underground and cause root rot and basil plate rot. Those can be commonly treated with a Captan powder or a good copper base powdered fungicide worked into the soil. Spraying an infected plant with a solution of either of these most likely will not work because the infection is inside the stem
.
