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- Pest Type: Insect
- Crops Affected: Corn
- Scientific Name: Anuraphis maidiradicis
- Pest Order: Homoptera
Adults are typically wingless, blue-green aphids with black heads and black or reddish-brown eyes. During the egg-laying period, the female has a gray body with a pink abdomen and a white, powdery coating. The various adult forms range from 1.5-2 mm long. Eggs are dark green, oval, and elongate; and less than 1 mm long. Nymphs are pale green with red eyes and resemble the adult shape; and they measure 0.3-2 mm long.
The corn root aphids pierce roots with their needle-like mouthparts and extract sap. As a result of this feeding, the foliage soon develops a characteristic yellowish to reddish tinge. Heavily infested seedlings become stunted, rarely growing taller than 25 cm. In addition, infested fields are likely to harbor many anthills. Damage is most likely in dry years.
The life cycle for these aphids consists of egg, nymph, and adult. Throughout their life cycle, corn root aphids are highly dependent upon ants, especially cornfield ants. In most areas, the aphids overwinter as eggs deep within the ant nest. In March or April, ants carry newly hatched nymphs to the roots of corn or weeds, particularly dock and smartweed. If corn seedlings are available, aphids are transferred to them. Later the ants feed on the aphids' honeydew secretions. First generation aphid nymphs feed on roots for 2-3 weeks before developing in to wingless female adults. By-passing the egg-laying stage, these mature aphids soon give birth to 40-50 live nymphs. After several generations, winged female aphids appear and fly to nearby fields, especially corn or cotton. After landing on ant hills, they are carried to the roots by ants. Eggs are laid for overwintering and are carried by ants deep into their nests. In no-till corn, 10-22 generations of corn root aphids are common per year.
Corn root aphid infestations can be prevented by a variety of cultural practices. Control of weedy hosts in the spring eliminates breeding and feeding sites for some of the first aphid generation. Cultural practices which stimulate rapid corn root growth greatly reduce early stunting by aphids. Deep tillage at least every other year weakens ant colonies and thereby decreases the chances that overwintering aphid eggs will survive. Crop rotation also prevents the buildup of large ant and aphid populations in any one field. If ant hills are present prior to planting, an insecticide application at planting may be advisable. If corn root aphids are found, consult local advisers for local thresholds and control recommendations.