Bird cherry-oat aphids and greenbugs on wheat
At one time, it was thought that the bird cherry-oat aphid caused very little direct yield loss to wheat except by vectoring BYDV. However, more recent research information from Oklahoma State University and the USDA-ARS suggest that the bird cherry-oat aphid is almost as damaging to wheat yield as is the greenbug. The data shows that if populations exceed 20 aphids per tiller before the boot stage, (400 aphids per foot of row) for 10 days, a 5% yield loss could be expected. If populations exceed 40 aphids per tiller for 10 days, (800 per foot of row) before boot, a 9% yield loss could be expected. Although its feeding causes no chlorosis or other visible damage to wheat plants, heavy infestations can also reduce grain quality, affect protein content and test weight, and even reduce protein assimilation by grazing cattle.
Still, the bird cherry-oat aphid causes the most damage by vectoring plant viruses, especially BYDV. Although the hot summer weather in Kansas is usually effective in decimating aphid populations, bird cherry-oat aphid can temporarily avoid extremes of temperature by feeding on the lowest parts of the stalk, at or below ground level. It is also able to feed actively in weather too cold for other aphids, such as the greenbug, enabling the bird cherry-oat aphid to effectively colonize seedling wheat quite late into the fall.
The bird cherry-oat aphid is usually held below economic injury levels by natural enemies such as lady beetles, lacewings, hover flies, and parasitic wasps. However, conditions that favor outbreaks of greenbug or Russian wheat aphid (for example, an abrupt shift back to cold temperatures after a warm spell in spring) also benefit the bird cherry-oat aphid. The bird cherry-oat aphid will often be found forming mixed colonies with these aphids when they are abundant. In such cases, decisions to apply pesticides should be driven by the numbers of those direct-damaging species and materials applied to control them should be equally effective against bird cherry-oat aphid.
If bird cherry-oat aphid is present alone, count the number of aphids present on each of a series of 25 - 50 randomly selected tillers across a zigzag transect of the field. Treatment with an insecticide broadly labeled for aphid control on wheat can be considered if an average of 50 or more aphids per tiller is present from boot stage up until heading. However, treatment with contact insecticides will not reduce the incidence of virus transmission.