The English grain aphid, Sitobion avenae, has been found in eastern and central South Dakota in high numbers on wheat. This is a relatively large aphid, about 1/10 of an inch long, light green to brown with black antennae, and clearly visible black cornicles. It is a known vector of barley yellow dwarf virus, (BYDV) but the major damage to wheat is caused by the aphid's direct feeding injury to the heads of small grains says Ada Szczepaniec, SDSU Extension entomology specialist.
"Foliage damage occurs until grain begins to head. Once heading initiates, these aphids move and aggregate at the heads and aggressively feed upon the ripening kernels," Szczepaniec said.
Szczepaniec encourages wheat growers to scout their fields. She says scouting should begin roughly 100 feet or 20 paces from the field edge. Individual stems and leaves should be inspected for aphids or signs of damage on 10 plants in five locations in the field.
She adds that field ants can be an indicator of an aphid threshold as they harvest the sugary secretion called honeydew that the aphids produce. The specific thresholds for English grain aphids are 30 per plant when wheat is in seedling stage, 50 when in boot to heading stage, five when wheat is flowering, and 10 or more during heading.
As for controlling aphids in the field, Szczepaniec says several insecticides with pre-harvest interval of 14-15 days are registered for aphid control.
"As we are getting closer to harvest, the pre-harvest intervals will become an important factor in selecting insecticides to apply against these pests."
It is always advised to scout before applying pesticides, as insecticide applications before aphids reach threshold have severe negative effects on populations of beneficial insects that can successfully suppress low levels of aphids.