By Janet J. Knodel
Extension Entomologist
High populations of aphids are being observed in field corn in the east-central areas of North Dakota (NDSU Corn IPM Survey). These aphids are several species including the bird cherry oat aphid, English grain aphid and corn leaf aphid. The critical period for injury by aphids is during tassel emergence through pollination. For corn leaf aphid only, treatment is recommended only when 50% of the corn plants have 100+ aphids per plant during tassel emergence and plants are drought stressed. There is no research available on the economic impact of cereal aphids (bird cherry oat aphid and English grain aphid) on field corn. It can become a pest problem when cereal aphids are concentrated in the ear zone and sooty mold is common during pollination (Pers. comm., Dr. Erin Hodgson, Iowa State University). In North Dakota, aphids are usually not an economic problem in field corn. Field scouting can determine if populations warrant an insecticide treatment. Natural enemies (lady beetles, aphid lions, syrphid flies and parasitic wasps) are often effective in reducing aphid populations. When natural enemies are present in large numbers, and the crop is well developed, farmers are discouraged from spraying fields.
