Oriental poppies

I have an oriental poppy that has already flowered once this summer.
Last weekend I looked at it and it had three more flower stems growing. However one looked diseased - the flower head was turning black and the stalk was bending over. I cut the whole stalk off.

As the week went on the remaining two also went the same way.

I sprayed it with bug spray but it didn't help.

Can anyone help me with what might have caused this?

Thanks

Feline