What bug is this?
These insects appeared all over some rudbeckia hirta in a sunny corner curbside garden. Leaves have turned yellow and curling. Other shrubs and flowers in the garden ( helenium autumnale, phlox subulata) do not appear affected. What are they and what might I expect to see happen?
These look like aphids, which suck plant sap and can sometimes cause leaf distortion. Despite their often high numbers and minor plant damage, they rarely cause lasting harm to the plants and sprays are not always necessary. The yellowing of the Rudbeckia hirta could also be due to root stress from excessive or needed moisture. We do not recommend fertilizing, as this has been known to benefit aphid populations. If you wish to treat them, options include insecticidal soap or horticultural oil: https://extension.umd.edu/hgic/topics/aphids-flowers. Thorough coverage is necessary for effectiveness (though do not treat the flowers) and avoid all sprays when temperatures are above 85 degrees F. Repeat treatments may be needed, though predators and parasites typically control populations sufficiently on their own