By Janet J. Knodel
Our first cereal aphids, English grain aphids and bird cherry oat aphids (Figure 1), were detected in wheat last week in Cass and Richland counties in southeast North Dakota. This is one of the earliest records of cereal aphids in North Dakota. The aphid populations were very low, about 1-5% incidence, in observed wheat fields. Cereal aphids are blown into North Dakota from the south, and continue to reproduce in the summer, having multiple generations until the fall. Minnesota and South Dakota also have reported low levels of cereal aphids in wheat (Source: B. Potter, SW MN IPM Stuff, UMN; A. Varenhorst, iGrow, SDSU).
Scouting should begin as soon as aphids are detected and continue until the heading stage of wheat. For a scouting protocol, walk a Z or W pattern across the field and inspect 20 randomly selected stems at 5 sites for cereal aphids. Calculate the percent of infested plants (incidence) with one or more aphids.
The economic threshold is 85% incidence prior to the completion of heading. Heavy infestations of cereal aphids can reduce grain quality (protein and test weight), especially in early growth stages of wheat. After the onset of flowering, the negative impacts of cereal aphid feeding are reduced (no yield loss). In addition to causing feeding injury, cereal aphids are vectors of barley yellow dwarf virus (BYDV). Symptoms of BYDV include stunting and leaf yellowing/reddening (often the flag leaf) progressing from the tip back toward stem (Figure 2). The earlier BYDV occurs in a field, the greater chance of yield loss. Several symptoms of BYDV can be confused with other abiotic disorders; therefore for positive diagnosis of BYDV, please send plants to the NDSU Plant Diagnostic Laboratory for an ELISA test. BYDV has been confirmed in SW MN (Source: Bruce Potter, SW MN IPM Stuff, UMN); however, we have not received any reports of BYDV in ND yet.