Figure 1. Soybean aphid colony on a leaf. Credit: A. Varenhorst
We are still observing small populations of soybean aphids throughout much of Eastern South Dakota. In the fields, these populations are appearing as “hot spots”, where a single plant may have as many as 200 to 300 soybean aphids on its leaves and stems. However, these hot spots are still spread out, and average populations within the fields are still well below the economic threshold of 250 soybean aphids per plant.
Does this mean that soybean aphids won’t be a problem for 2017? The quick answer is no. Past experiences with the soybean aphids have demonstrated to us that they are capable of reaching economically damaging populations very quickly. Previous research from the University of Minnesota determined that under optimal conditions (temperate at approximately 82°F and an absence of their natural enemies) soybean aphids can double their populations every 1.3 days. However, we know that we don’t live in a perfect world and those conditions don’t actually exist. We anticipate that under normal field conditions, soybean aphids may double their populations every 3 to 14 days. Based on this, it is still possible that soybean aphids could reach populations that warrant management.
We continue to recommend scouting soybean fields on a weekly basis to ensure that a population explosion is not missed. If populations of soybean aphids are observed, scout your fields and follow the recommended threshold of 250 soybean aphid average based on 20 plants.