By Anitha Chirumamilla
Bird Cherry Oat Aphids spotted in winter wheat
Bird cherry oat aphids (BCOA) were spotted in winter wheat last week. These are pear-shaped, olive green aphids with a rusty brown patch at the posterior end (Figure 1). BCOA primarily cause damage by feeding on plant sap, denying the plant nutrients which results in yellowing, stunting and yield loss. They can also cause damage by transmitting plant viruses like barley yellow dwarf virus in wheat. The majority of winter wheat fields in South Dakota are at the heading or flowering stage which means they have passed the susceptible stage for yield loss from aphid feeding damage. However, spring wheat will be at a higher risk as populations continue to build.
Figure 1. Bird cherry oat aphid.
Early and frequent scouting is important for successful management of aphid populations. Scouting is done by counting aphids on individual stems. More information on scouting, economic thresholds, and insecticides labelled for application on wheat aphids can be found in the iGrow article Look Out for Cereal Aphids in Wheat.
Barley Yellow Dwarf Virus in winter wheat plants
Several winter wheat plants infected with barley yellow dwarf virus (BYDV) were spotted in fields during last week’s wheat walks. The plants with the virus had a purplish discoloration at the tip of the flag leaf which is an early symptom of barley yellow dwarf infection (Figure 2). Although the symptoms are seen in the spring, the actual transmission of virus took place from aphids last fall. Unfortunately, there is nothing we can do to control the virus in the infected plants. Preventative measures like resistant cultivars, delayed planting, and insecticide seed treatments might help prevent the fall colonization of aphids in winter wheat thereby reducing the transmission of virus.
Figure 2. Barley yellow dwarf virus infected wheat with purplish discoloration at the tip of boot leaf.
Wheat Streak Mosaic Virus spotted near Winner, SD
Figure 3. A wheat streak mosaic virus infected field near Winner, SD.
Winter wheat fields heavily infested with WSMV were spotted near Winner last week (Figure 3). The infested plants were stunted with bright yellow streaks on the leaves (Figure 4). The virus is spread by wheat curl mites (Figure 5) from neighboring infected wheat, volunteer wheat, and/or grassy weeds. Similar to BYDV, WSMV infection in winter wheat that causes significant yield loss occurs the previous fall. There are no effective chemical treatments to manage the wheat curl mites or WSMV. Prevention is the only strategy to escape the virus and vector by avoiding volunteer wheat, using genetic resistance, and delaying the planting date.