Planthoppers look like large leafhoppers and have similar feeding habits. They may also be known as flugorids and lanternflies. A common planthopper is one of the flatids which is wedge-shaped, flattened and pale green. Planthoppers feed on plant juices and produce honeydew. They feed on a wide variety of herbaceous ornamental plants but cause little damage. They are generally noticed because of the white waxy material produced by the nymphs (see photo below). The nymphs are covered by the waxy material and may also leave some behind on the stems of plants they are feeding on.
Planthopper nymphs on a stem. Photo: David L. Clement, University of Maryland
Flatid planthopper adult. Photo: Kevin D. Arvin, Bugwood.org
No control is necessary. However, you can wash it off the stems of your plants with a stream of water.