Question
a large amount of our cone flowers are "cut off" about two inches beneath the flower.
a little black line appears on the stem, and the flowers fall over and hang from the cut...?

Answer
Dan:
I would suspect an insect, perhaps a caterpillar type critter. It is best to capture and ID a specimen. Collect in a small jar and carry to your nursery/garden center to get an accurate. You may have to check your flowers several times during the day, especially late evening to find these things.

Steve