Many agronomists and producers have noticed a large number of aphids present in select corn fields the past two growing seasons. The two predominant species are the corn leaf aphid (Rhopalosiphum maidis) and the bird cherryoat aphid (Rhopalosiphum padi). Currently, there are no economic threshold levels available for producers to use when debating the need for management strategies beyond tasseling. A trial was initiated at the Northwest Research Farm in 2009 to study the impact of these aphid species on corn grain yield.