I have grown some Gloriosa Lilies [Gloriosa rothschildiana] from seed. Last year, after a few sidetracks along the way, they finally got big enough to bloom. It was short-lived. Something apparently attacked them, with the result there was a dead section about 12-15" up the stem. Since they don't grow secondary stems/branches from dormant buds at the base of the leaves as in most other stem plants, the lily is then essentially dead (until a new sprout eventually comes from the tuber).
The same thing occurred this year. The lily stalks were more robust, and the flowering heads larger than last year, but once again, as soon as a couple stalks started blooming, the dead sections appeared.
Eventually every stalk over 18" had the dead spot. The first pic above shows a small speck like the stem had been stung or otherwise invaded, but in person it did not look like anything. I have never seen an obvious cause of the damage on any stem.
Anyone else ever had this problem?