Corn leaf aphid: Rhopalosiphum maidis

Corn leaf aphids occurs worldwide, but do not overwinter in extreme northern states or Canada, where they may be brought in on prevailing winds. In Connecticut, they may not survive cold, snow-less winters, and instead migrate up on airstreams. This aphid is blueish-green or black, with black legs. Host plants include many common grass weeds (barnyardgrass, crabgrass and foxtail) and most cereal crops (corn, barley, rye, oats, wheat, sorgham and millet).

Life Cycle: Corn leaf aphids overwinter as females on the host plant. No males or egg stages occur. Females produce live young which mature in as little as 6 days. There are up to 9 generation per year in Northern states.

Damage: Corn leaf aphids first colonize whorl leaves and the immature tassel. Populations may become numerous enough to interfere with pollen shed and to stunt plants. Maize dwarf mosaic virus may be spread by the corn leaf aphid, though the most important vector for this disease is the green peach aphid. The presence of high aphid populations or honey dew on corn ears can render the ears unmarketable. Honey dew on ears has been reported to increase the number of corn earworm moths attracted to the plants. Ample rainfall and soil moisture during the silk stage of development can reduce or eliminate damage.

Monitoring: Start monitoring for aphid colonies while scouting pre-tassel stage corn for European corn borer or fall armyworms in late July or August. Pre-tassel stage sprays may be needed in dry seasons, particularly on varieties with yellow tassels, when 50% of the plants are infested.

Cultural, Biological and Chemical Management: Sweet corn plantings that are seeded before 10 June are not bothered by corn leaf aphids. Varieties with purple or green tassels seem to be less susceptible to aphid build-up than those with yellow tassels. There are many natural enemies (lady beetles, lacewings, flower fly larvae, predatory midges, pirate bugs, Braconid wasps) that help reduce aphid numbers, but they may not provide adequate control especially in dry seasons after warm winters. Providing adequate irrigation during the silk stage can reduce or eliminate aphid damage. Growers that use selective insecticides (i.e. B.t products or spinosad) for most early and mid-season sprays seem to have fewer problems with corn leaf aphids than those choosing broad-spectrum material like synthetic pyrethroids. Also, if selective materials are used routinely,  and aphid problems do occur, a single application of a material (i.e. Warrior) that normally would only suppress the population, can produce complete control. See the New England Vegetable Management Guide for a list of registered products that are effective on this pest.

By: T. Jude Boucher, University of Connecticut, Cooperative Extension System

January 2005, Reviewed 2012

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