Aphids in winter wheat have been reported in Hand County in central South Dakota as well as Hanson, Davidson and Aurora counties in the southern portion of the state.

According to Ada Szczepaniec, SDSU Extension entomology specialist, numbers were ranging from six to 15 aphids per plant and some visible damage from the aphid feeding was also observed.

"The warm fall weather is likely the culprit," Szczepaniec  said, encouraging wheat growers to scout emerged winter wheat fields for aphids. "Warm temperatures are forecasted to persist for several more days and aphids are more likely to increase in numbers in these conditions."

She explained that aphids can survive in whorls of wheat plants for some time when temperatures dip below freezing, but aphid populations will decline quite quickly once nighttime temperatures drop this fall.

The aphids most often reported on wheat were the bird cherry-oat aphids. These are dark green aphids with a brown band running across their abdomens. Szczepaniec said they are usually found at the base of plants at the soil level in the fall. "Bird cherry-oat aphid can transmit Barley Yellow Dwarf Virus and can be a concern in winter wheat," she said.

Treatment recommendation

The recommendation is to treat with insecticides if there are on average 20 bird cherry-oat aphids per plant or 15 to 25 aphids per linear foot of row from seedling emergence in the fall to heading stage of wheat the following spring.

Szczepaniec said greenbug aphids have also been reported on winter wheat, especially in the southern counties. These aphids are smaller than bird cherry-oat aphids, bright green in color, have barely visible black cornicles and long antennae. Thresholds for greenbugs are higher - 25 to 50 aphids per linear foot of row.

For more information on these and other pests of field crops got to iGrow.org and use the search bar to locate the pest of interest.