This is a healthy stand of yellow cone flower (ratibida pinnata) growing in our garden. Yellow coneflower also grows in another area that is hidden from the public by a fence between buildings. This year the other stand was not so healthy.
Black aphids are fast to reproduce and can suck the life out of new growth on plants they attack. Growth slows, foliage yellows, blooms are few.
Since this is a habitat garden where no pesticides are used ever, a situation like this can be a learning experience. Instead of using a hose to try and dislodge the aphids we decided to wait,watch, and see what happens when left to achieve that natural balance between predator insects and plant eaters.
It was not long before hover flies,lady bugs and parasitic wasps were on the job. It took a couple of weeks before the black aphids disappeared but they are gone now. Predators had a food source and reason to lay eggs and hang around. No other plants in the area were affected.
This last picture is of the yellow cone flower in recovery. The yellowish leaves are regaining health and new blooms are forming. It is much shorter and less full than last years plants in this spot. I will take weekly pictures to record what happens now...
Cutting the plants back to the ground and letting start over was an option if the damage had been more severe. Yellow cone flower is a hardy native that recovers well from drought and the few pests that do it harm. We decided to let it be. Today a good rain fell to aid a quick recovery.