Cereal Aphids on Wheat Heads (07/01/21)
Low numbers of English grain aphids, 30-50 aphids per head, are being observed on wheat heads in eastern ND. Producers are concerned about the impacts of aphid head-feeding on yield. However, the wheat crop is maturing quickly, in flowering to dough stages, due to the drought and heat pushing the crop. This will help mitigate any negative yield impacts from the aphids. Research indicates that cereal aphids will not cause any yield loss after the heading stage (Zadoks 59 and Feekes 10.5), but seed weight can be slightly reduced if very large numbers of aphids on heads. Research on the relationship between seed weight and aphid densities was a flat line for flowering and dough stages indicating that as aphid populations increased to 2,000 aphid days there was little reduction in seed weight. In contrast to an earlier crop stage, boot, there was a slight decrease in seed weight as aphid density increased. Research on cereal aphid infestations during the later stages of wheat and on drought-stressed wheat is limited in the Great Plains.
While scouting, it was easy to find predators such as, lady beetles, aphid lions, syrphid fly larvae, and aphids parasitized by wasps (called mummies), which play a major role in reducing aphid populations (see photos on next page). One adult lady beetle consumes about 300 aphids per day, and larvae about 30-50 aphids per day. One lacewing larva consumes about 200+ aphids per week, and one syrphid fly larva about 400 aphids during its development. When natural enemies are present in large numbers, and the crop is well developed, farmers are discouraged from spraying fields.