David Owens, Extension Entomologist, email@example.com
Now is a good time to scout small grain fields, and especially barley fields, for aphids. Barley tends to be planted earlier than wheat allowing aphids more time to colonize and reproduce. Barley is also generally more susceptible to barley yellow dwarf virus than wheat. There are several species of aphids that may be present in fields. English grain aphid and bird cherry oat aphid are the most common. English grain aphids are green with long black antennae, black feet, and black cornicles (tailpipes). Winged EGA is brown and green. Bird cherry oat aphid is generally associated with more severe BYDV incidence. It is a dark, olive-green aphid with red at the base of the cornicles. Winged females are black. When scouting, look at 1 row foot or 1 square foot in multiple locations in a field. I like to walk a large circular route with 6 to 10 stops. When looking at the plants, if you look towards the sunlight, aphid silhouettes are easy to see as they are backlit. A third, generally less common, species that may be present is greenbug. Greenbug looks similar to English grain aphids, but the antennae are green, the tailpipes are green and there is a blue stripe right down the middle. Sometimes English grain aphid also has a blue stripe on its back, but it is more prominent with greenbug.
There are a couple of suggested thresholds for aphids in small grains. North Carolina State University uses a threshold of 20 aphids per row foot in fields where BYDV has been a problem and cold weather is not forecast. Cold weather means daily average temperatures around 40 degrees F. Other states use a threshold as low as 6 aphids per row-foot.
If a field is near or above threshold and the farm had BYDV last season, scout the field! Aphid management generally only pays for itself when performed in fall or late winter (no later than the end of February). Last season, we experienced unusual and, in some cases, severe BYDV evident in March. Some of these fields had very low aphid numbers going into ‘winter.’ Last winter we experienced less than half the number of days below 32 F that we normally receive, and by the end of February aphid counts in many locations exceeded 100 per row foot.
Pyrethroids do an excellent job controlling aphids. For barley producers, we have Endigo ZC or ZCX, but only if a thiamethoxam seed treatment such as Cruiser, was not used. Other labeled insecticides for small grains can be found at by searching for UD small grain insect control 2020.
For more information about barley yellow dwarf management, please see the extension bulletin “Barley Yellow Dwarf in Small Grains in the Southeast” which can be found at: https://entomology.ca.uky.edu/files/efpdf1/ef150.pdf.