English grain aphid - Sitobion avenae Fabricius,
Bird-cherry oat aphid - Rhopalosiphum padi Linnaeus
Appearance and Life History
A number of aphid species may be found on small grains in the Midwest. The two species described below are the most common aphid pests of small grains in Indiana.
English grain aphid occurs both as wingless and winged forms. The wingless form is pale green with long black antennae and cornicles (the two projections from their posterior end). The winged English grain aphid is identical to the wingless form, except that it has wings and dark lobes on its thorax (the area immediately behind its head). English grain aphid is similar in appearance to the greenbug. However, once full-grown, it is almost twice as large.
English grain aphid females overwinter in areas of heavily seeded young small grain plants or in clumps of volunteer oats, rye, or wheat. In the spring, they begin to give birth to live young (no eggs laid) and feed on the leaves and stems of small grain plants. As the heads begin to form, clusters of aphids may feed on the developing kernels resulting in shriveling and shrinking of the grain.
Once their host plants are harvested, English grain aphids migrate to wild or cultivated grasses where they spend the remainder of the summer. In the fall, they move into newly seeded small grain fields or onto volunteer grain plants.
The life habits of the bird-cherry oat aphid are very similar to those of English grain aphid. It too may appear either wingless or winged. The wingless form is olive-green and often has a large reddish-brown spot or spots on the posterior part of its body. The winged formed is predominantly black.
Both of these aphid species injure small grains by sucking plant juices from the leaves, stems, and/or heads. However, they can also cause severe losses by serving as vectors of barley yellow dwarf virus (BYDV), a disease that causes yield reductions in small grains in the Midwest. Bird-cherry oat aphid is known to be a very effective transmitter of BYDV.
If during regular field visits, one observes a significant number of English grain aphid, bird-cherry oat aphid, or any other aphid species, carefully examine 20 stems in each of 5 areas of the field. Count and record the number of aphids found to determine the average number of aphids per stem. Record the number of parasitized aphids (mummified; gray to brown and balloon-shaped) and any beneficial insects, such as lady beetle adults and larvae and lacewing larvae. Finally, note the stage of development of the plants.
Corn Insect Control Recommendations: E-series 220-W (PDF)
Control may be advisable if an average of 20 or more aphids per stem are noted while plants are in the tillering stages (growth stages 1-5); an average of 30 or more aphids per stem when plants are in the pre-boot stages (growth stages 6-9); or an average of 50 or more aphids per stem when plants are in the boot, heading, and/or ripening stages (growth stages 9-11).
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.