Green soybean stems at harvest is far from a new phenomenon. Farmers were noticing green stems in some fields as far back as the early 1980s. It’s a topic of conversation among farmers this year because it was relatively widespread.

“There can be a variety of causes, and exactly what causes it in every case is not well understood,” explains Steve Gauck, a regional manager for Beck’s, based near Greensburg, Ind. Beck’s sponsors Soybean Watch ’23.

“Some people believe genetics may be part of it,” Gauck notes. “My best explanation, especially in years like this one, is that it is likely related to stress and what plants endure during the season. For example, if it’s dry — as it was early and late this year — plants tend to get stressed. The signal going through the plant if it’s dry late in the season is to begin to shut down.

“Then, if it rains, some plants may perk back up. The plant moves sugar back through the plant. As that happens, plants and stems either green back up, or hold onto their green color instead of drying up right away. That scenario can result in stems that are still green as harvest approaches.”

Practical implications

So, does it matter if stems are green at harvest? That may depend on how many stems are green, and if they are tough enough to interfere with harvesting efficiently, Gauck says. Too many green stems can make it harder to get the crop through the combine. Throw in some green weeds, like foxtail patches, and it can become a long afternoon with stops and starts, working through crop and weed material that does not feed through the machine well.

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“The other big thing we see is that if stems are still green, people tend to misjudge the moisture content of soybeans in the pods,” Gauck says. “You may be thinking that if there are still a lot of green stems, moisture content may be too high to run the field. However, we had multiple reports this year of soybeans testing as low as 9% moisture when there were still some green stems in the field.”

Once soybeans drop to such a low moisture level, you’re likely to see increased harvest losses. Shattering at the head where the reel goes into the crop will take away some potential yield, Gauck says.

“It pays to be checking moisture content in the beans themselves as harvest approaches,” Gauck says. “If they’re down to the level where you don’t get dock and your machine can handle the extra load of greener material, it probably pays to harvest and get them out.”