Soybean Aphids Making a Comeback?

Soybean aphids have been found in a few fields in Ontario, ranging geographically from Dresden to Ottawa. Though some of these aphids could have come from neighbouring buckthorn, it is also likely that many blew in from other regions during the storms a week or so ago. The more advanced a field is in growth stage, the more likely the aphids found them. So far, with the exception of a couple of very early planted research plots, most fields have only 5 to 10% of the plants infested with 1-15 aphids per plant. These are not alarming numbers but it will be up to the natural enemies as to whether these initial colonies get a chance to build up or get eaten up and disappear.

No thresholds are established for the V stage soybeans but it is questionable as to whether we'd see a yield response when spraying this early and the risk to killing any establishing natural enemies is high and could result in the aphid populations flaring up. But you should still scout to determine if the aphids and predators are present. Focus on the earliest emerging fields first that were not treated with Cruiser. Most of the aphids will be on the newest trifoliates starting to emerge. If fields are found with a consistent population of aphids on 50% of the plants or more, please contact me as we have several research trials we'd like to conduct on these early season infestations.