Photo 2. Bird cherry-oat aphids on a corn leaf. Cereal aphids colonize multiple grass hosts. Note the dark olive color and orange band around the cornicles.
Photo 3. Damsel bug adults are just one of many beneficial insects that feed on aphids and help control populations.
In addition to heavy cereal aphid populations causing direct damage by feeding on plant sap, these species can transmit virus diseases, most notably, Barley yellow dwarf virus (BYDV).
Barley yellow dwarf virus
Dr. Madeleine Smith, U of MN Plant Pathologist, will assay a sample of these to see if they are carrying BYDV. Fortunately, BYDV symptoms haven't been seen yet on local winter wheat and there may not be wide-spread overwintered BYDV infections for the aphids to spread disease from. Unfortunately, the aphids could have brought the virus with them from the south.
Symptoms of BYDV are yellowing of foliage (red in the case of oat, hence the other common name (oat red leaf) (Photo 5). Severe stunting, increased tillering, sterile spikelets, and reduced heading can occur depending on when plants are infected. Symptoms and yield loss of this disease are more pronounced when plants are infected when young. Symptomatic plants are often found in circular areas (infection centers) where disease started in the field and where colonizing aphids carrying the virus further spread the disease.
Cereal aphid populations are very sensitive to environmental conditions and natural enemies.
Bird cherry-oat aphids tend to colonize plants low on the stem, often under leaf sheaths while English grain aphid and green bug colonies are usually higher on the plant. Examine all parts of the plant when you are scouting aphids in cereal crops.
Thresholds for individual aphid species have been developed but a general economic threshold for cereal aphids in wheat, oats and barley 85% of the stems with at least one aphid prior to heading.
Early, prophylactic insecticide treatments cost money and can make things worse by removing natural enemies. Populations after flowering have not been shown to reduce yields.
Photo credits: Bruce Potter, University of Minnesota.