Reports from extension field crops specialists across Iowa on July 24 indicate that soybean aphids have not reached the economic threshold of 250 aphids per plant in most fields. Soybean aphids can be found, but it appears that overall the populations range from just a few aphids per plant up to 30-50 per plant. There was a report of several fields being sprayed in northwest Iowa near Emmetsburg, but no aphid counts were given for these fields so the population size relative to the economic threshold is unknown.
A teleconference on July 18 with extension entomologists from several Midwestern states revealed that soybean aphid populations also are at low levels throughout the Corn Belt. There was no field spraying for aphids in Nebraska, Wisconsin, Illinois, Indiana, Michigan, or Ohio. Only northern and central Minnesota soybeans were experiencing populations above the economic threshold.
The last week of July and the first week of August will be the remaining critical weeks for soybean aphid scouting in Iowa. All soybean fields should be scouted at least once, and probably twice, during this time frame so that potential economic infestations are not overlooked. Right now 2006 appears to be a year when the soybean aphid fizzled. For now, we can only hope and scout. The next two weeks will determine how soybean aphids will be remembered for the year. Stay tuned.
Winged soybean aphids fly from buckthorn to soybean where they give birth to live aphids. (Marlin E. Rice)
This article originally appeared on page 213 of the IC-496(21) -- July 24, 2006 issue.