The soybean aphid watch continues across the state with many anxious crop scouts still looking for their first sighting, and hoping they haven't overlooked the pest in the fields that they just scouted. Mark Carlton, Extension field crop specialist, confirmed a small hotspot of soybean aphids south of Knoxville in Marion County on July 12. He noted that in a 10-foot circle there were 200-1,000 aphids per plant and each leaflet had two to three winged aphids. These aphids were originally found by Aaron Crane, New Alliance FS, Knoxville. This is not a situation that would justify spraying the entire field, but a spot treatment of a registered insecticide might be appropriate to extinguish this small infestation. Obviously, the winged aphids will be moving to other plants in the field and possibly neighboring fields.
Additionally, Matt O'Neal, soybean aphid researcher at Iowa State University, is surveying along a transect from Decorah to Ames, and then from Des Moines west along I-80. Matt and his students are scouting two to three fields every 20 miles along this transect and last week found aphids at only one location about 120 miles west of Des Moines.
So the aphid situation is still good news. The next several weeks will determine if we escape this pest or experience serious problems. Be diligent, keep scouting weekly, and don't spray until the population across the field reaches 250 aphids per plant.
This article originally appeared on page 94 of the IC-492(16) -- July 19, 2004 issue.