In surveys of apple-production areas east of the Cascade Mountains of Washington, broadleaf plantain, Plantago major Linnaeus (Plantaginaceae) was common throughout while narrowleaf plantain, P. lanceolata Linnaeus, was most common south of Orondo, Douglas County (47.7° latitude). Rosy apple aphid was the most common aphid on these two herbaceous plants; however, colonies were scarce, on only 19% of broadleaf and 11% of narrowleaf plantain samples. Colonies were also generally small, fewer than 25 individuals. Adult rosy apple aphid was collected on plantain from late May through October. Adults reached their highest levels in July before declining in August. Colonies increased again in September and October. Relatively few predators (mainly syrphids) and parasitoids (two species of Aphidius) were found on plantain. On apple, the most common predators were the mirid Campylomma verbasci (Meyer-Dür), earwigs, coccinellids, cecidomyiids and syrphids; the most common primary parasitoid was Lysiphlebus testaceipes (Cresson). Secondary or hyperparasitoids consistently outnumbered the primary parasitoids. Plantains growing outside of orchards but within 1 km of apple trees had the highest incidence of RAA infestation. The potential for management of RAA on its summer hosts is discussed.