The alarm has sounded. Soybean aphids are in Indiana. And not just inside the border – they're in several areas in the northern half of the state. This is one pest that you don't want to ignore. People who ignored them in the past lost 10 to 15 bushels per acre of soybeans. That could amount to between $100 and $150 per acre – way more than enough to pay for treatment.

Aphids are back: Soybean aphids are back in Indiana, at least from Boone County north. Scout carefully before you spray. (DuPont Pioneer- Marlin E Rice photo)

However, Mark Lawson, a farmer and Syngenta agronomist, says you only want to spray for them if it's justified. The same spray that takes out aphids also takes out beneficial insects that eat aphids. It's only when the aphids out run the beneficial insects and threaten to take over that he suggests stepping in and taking control with chemicals.

Lawson found heavy infestations in Fulton County a few days ago. Another Syngenta rep found them near Westfield in the northern part of central Indiana. Lawson has found a few in Hendricks County, but as of just a few days ago, they weren't enough to worry about yet.

Lawson believes it's the largest outbreak in Indiana in five years. Beans will begin to look wilted as aphids suck out plant juices if the infestation is heavy. It takes 250 per leaf before triggering treatment, which sounds like a lot – and it is. However, the population can explode so quickly that it can go below threshold to above threshold almost before you can order an application and the applicator gets the field sprayed, Lawson says. If you in a hot bed area, you need to be paying close attention to what's happening in the field.

"Scout and turn over a lot of leaves before you pull the trigger and spray," he says. "You will kill good insects too."

However, there is a point at which the aphids take over and drop yield. You want to step in before that happens, he concludes.