Marigold

Marigold may have been gardener's best friend as it is a good companion plant to send away annoying pests. Marigold had been on my planting list last semester. Unluckily, it hadn't been effective to keep pests, in this case aphids, away, but the other way around 
it had been heavily infested with aphids! 

It especially attacked my African Crackerjacks. 

  Until one point, I decided to chop them off and discarded them.

                       Does anyone know why?