The picture provided appears to show a wooly aphid. Aphids use their needle-like mouth parts to be feed on sap from plants. They can feed on unopened flower buds and the underside of young leaves and stems. They are common and, in most cases, the sap lost is not significant to the plant. They apparently cause no permanent damage with little or no damage to the overall health of the plant. Any damage done mostly affects the plant’s appearance. Treating for an invasion of aphids is only necessary or recommended if significant damage is occurring.

Natural enemies play a very important role in aphid control. Natural predators such as lacewings, lady beetles, hover flies, and parasitic wasps can control aphid populations below acceptable levels. Another control method is syringing the plant. This consists of hitting the aphids with a forceful stream of water from the garden hose. Aphids are not strong insects and even a good rainstorm can knock them off. Check the plants regularly as populations can grow rapidly. Syringing may be needed again. Pesticide applications are not usually recommended as they will kill the parasites and predators that are effective aphid control.

Sources: Iowa State University, OSU, University of Minnesota