Green and purple soybean stems appearing

By: Daren Mueller and graduate students, Xavier Phillips and Chelsea Harbach

Some are noticing plants with green, yellow or purple stems. A few years ago we wrote a longer article on green stem, but since then we have been trying to sort through the root causes of green stem disorder. Here is what we now know:

• Soybean plants with reduced number of pods can have stems stay green, or perhaps yellow, longer than expected.
• When there are fewer seeds (or possibly smaller seeds), plants store carbohydrates in the stem, which can lead to increased incidence of plants with green stems at harvest maturity.
• Both biotic and abiotic stress may cause pod abortion.  
• Spraying fungicides of certain chemistries and removing 50 percent of pods will increase the incidence of green stems at maturity more than just spraying fungicides or removing 50 percent of pods alone.
• A disruption in the source-sink relationship can also lead to purple stems. Increased levels of anthocyanin cause this, especially on soybeans with delayed maturity (green stems and/or leaves) with mature pods. The plant is still producing carbohydrates that are being converted to anthocyanin and show up in the stems