CORN LEAF APHID: Rhopalosiphum maidis, Aphidae

ADULT: A small (1/16 to 3/32 in.), medium green to black, elliptical-shaped aphid. Legs and cornicles are short and dark green to black. The end of the abdomen and bases of cornicles are not reddish as in birdcherry aphids. Winged females have a black head and thorax, and a green abdomen.

NYMPH: Winged or wingless adult females deposit live nymphs, skipping the external egg stage in Florida.  Nymphs are light to medium green with legs and cornicles like adult, and dark areas around bases of cornicles. Nymphs molt several times to adult in 7 to 10 d.  There is no pupal stage in aphids.

GENERATION TIME: 7 to 10 d.

HOSTS: In Florida, these aphids feed on corn and other wild and cultivated grasses.

DAMAGE: Corn leaf aphids have become a greater problem for sweet corn during the last several years. These aphids feed mostly within the whorl of corn and other grasses and are most apparent at or just before tassel push.  This can result in poor pollen shed and fertilization.  Adults often leave plants as whorl disappears with emerging tassel, or continue to produce nymphs in leaf sheathes.

CONTROL: Many types of natural enemies may control these aphids under low pesticide input situations, such as in field or silage corn.  However, these aphids appear in sweet corn at a time when pesticide use increases for armyworm, thereby greatly reducing the potential impact of their predators and parasitoids.  Pathogens kill many winged adults before they begin producing nymphs.  Efforts toward chemical control of this aphid are more effective when they are exposed on the emerging tassel. They are more susceptible than birdcherry oat aphids to pesticides frequently used for armyworm control.  Formulations, rates, and pre-harvest intervals of insecticides for corn leaf aphid control are listed below for sweet corn (Table 1) and field corn (Table 2).