The number of soybean fields showing spots of bright yellow leaves that we saw on a Sunday afternoon drive through southern Indiana in early September was striking. I didn’t have my Nikon camera that I use for work. Ah, but I had a smartphone!
I asked my wife, Carla, to pull over many times, trying to capture the right image. It looked like classic spider mite damage to me. Most of the yellowing was along the outer edges of fields, although some was showing up farther out in the field, and it was in the upper leaves.
Two things didn’t quite add up, though. I didn’t see any evidence of mites on leaves, and while not super-green, roadside ditches weren’t bone-dry-brown either.
The next morning, I texted a photo to Steve Gauck, sales agronomist for Beck’s, based near Greensburg. He’s the agronomist who monitors the Soybean Watch ’19 field.
His answer based on the photo alone was direct and to the point. “It’s potassium deficiency, Tom,” he replied by text. “I’ve been seeing it, too. There may be enough potassium there in the soil, but the roots can’t get it.
“Many fields were planted wet, and soil compaction is an issue in some places. It may have affected rooting and the plant’s ability to take up nutrients.”
I’m certainly glad I didn’t start telling people it was spider mites! Since then, several other agronomists have confirmed what Gauck told me. Thank goodness for technology!