Last year it was aphids.
This year, there was one hot day in the greenhouse after spending two weeks longing for sun in my mudroom - these guys were toast.
I'll start a few more from seed and see if I can coax them into blooming before winter... but I think in a past life, I wronged someone who had something to do with zinnias.
(The tomatoes and nasturtiums and sweet peas along with many others are looking FANTASTIC. It's just the zinnias. I'm cursed.)