This is a sort of defect I tend to think is weather related. Usually
that means freezing, but in this case the split shown in your photo has
occurred when the bloom stalk is forming in hot weather. I've seen
this effect in late season iris blooms. Is it possible here? Did this
stalk form under hot conditions perhaps? Dry weather might be required
as well. Here hot and dry conditions tend to go hand in hand.
Texas Zone 7b, USA