David Hill wrote:
Really? I thought sweet peas would just die off if the growing tip
was nipped off lower than side shoots (hence why they don't survive
when mice nibble)

If you notice the OP says "mildew-infested perennial sweet peas"

Ah, I missed the 'perennial' in the post, which isn't in the subject.
Yeah, fair enough. My parents have those and can't get rid. :-)