It’s a safe bet that once you see this many molted skins, populations are doubling quickly and will be over the threshold soon.

It’s hard to believe how far we’ve come in understanding and managing soybean aphids. I still remember that first invasion—my dad calling the local co-op to figure out what this mysterious pest was and how to deal with it. 

Several years later, I began my career in agronomy near Fergus Falls, MN—often described as the epicenter of the soybean aphid. And for good reason: buckthorn. 

The Buckthorn Connection 

 Buckthorn is the primary host for the soybean aphid. Its life cycle is both simple and complex: 

• Simple in that an aphid hatches on a buckthorn plant, then feeds on soybeans. 

• Complex in the journey between hosts. 

Once they hatch on buckthorn, multiple generations are produced without mating. Eventually, winged aphids appear and migrate to soybean fields. Once there, they multiply rapidly—producing both winged and wingless generations—before heading back to buckthorn in the fall to overwinter.  

The Impact on Yield 

Left unchecked, soybean aphids can cause significant yield loss. Thankfully, years of research have given us an effective set of tools to manage them. 

One of the most valuable defenses? Beneficial insects—the natural predators that feed on aphids. That’s why it’s important not to treat too early. Waiting until populations reach the established economic threshold of 250 aphids per plant allows these beneficials to work for us as long as possible. 

Nature’s Allies: Fungi and Beneficials 

Entomopathogenic fungi—naturally occurring, aphid-killing fungi—can help, too, when conditions are right (moderate temperatures and high humidity).

Together with predator insects, these biological controls can keep aphid populations in check for much of the season. 

Chemical Control—When It’s Needed 

Once the 250-aphid threshold is reached, several effective insecticides are available. However, soybean aphids have developed resistance to certain products—particularly pyrethroids—making responsible insecticide use even more important. 

That’s another reason to avoid spraying before thresholds are met: we want to slow the development of resistance and preserve the effectiveness of available products. 

Role of Seed Treatments 

Soybean insecticide seed treatments can be highly effective at delaying the first flush of aphids. While season-long control isn’t likely, they can provide a helpful head start. 

Key Takeaways for Growers 

• Scout early and often for both aphids and beneficial insects. 

• Wait for the 250-aphid threshold before spraying. 

• Use diverse control strategies to protect yields and slow resistance. 

Soybean aphids are a serious pest, but with smart management, we can keep them from taking a serious bite out of our bottom line.