Black aphids love nasturtiums. Love them to death, in my case. I’d never seen a black aphid before I planted nasturtiums last year. They didn’t appear to move beyond my nasturtiums, so I simply observed.
I have been using nasturtiums in the garden as a natural pest control. They “repel squash bugs and whiteflies and draw beneficial insects”, according to one of my books. What I couldn’t decide last year was if nasturtiums drew pests away from my other plants or if they drew pests to the garden more generally, serving as a jumping off point.
The black aphid also loves cosmos. A volunteer cosmo was twining stalks with a tomatillo plant. The young cosmo stalks were covered with black aphids, while only a few peppered the nearby tomatillo stalks. Interesting. But not interesting enough to leave alone, because I am now also finding patches of black aphids on my beans. Not cool.
Last night I filled a spray bottle with water and dish soap and went to town on the dense aphid patches. This morning, the aphids appear…unaffected. Was it supposed to be special soap?
UPDATE 8/13: The soap treatment worked, though I had to repeat it a few times – not because it wasn’t killing aphids, but because more aphids appeared. I also helped myself out by removing the most heavily infested (non-edible) vegetation – the dying nasturtiums next to the beans, the cosmo plant intertwining with the tomatillos. I also added a few drops of oil to my soap-water mixture.