The challenges for 2015 continue to develop. Another issue growers are facing is green stemed soybeans. There are two distinct types of green stems, Green Stem Syndrome or simply stay green soybeans. In the case of stay green, the soybeans simply mature at a slower rate and the stems, leaves and pods all remain green. Stay green can be attributed to varietal differences, fungicide applications or some herbicide applications. In the case of Green Stem Syndrome, the stems remain green after pods have matured. Sporadically throughout the field you will also notice that several plants will retain their petioles and leaves on the upper nodes and can even have green pods on upper nodes.
The causes of Green Stem Syndrome are not actually known. Many times the syndrome is believed to be associated with diseases such as Bean Pod Mottle Virus (BPMV) or Cercospora, but the green stems are not a consistent symptom with these diseases. Another theory is that late-season stress caused by weather, disease or insects causes pod loss. Loss of pods or even seeds causes the soybean plant to reduce the need for sugars and nutrients (photoassimilates). The unneeded photoassimilates remain in the stem, causing the stem to remain green. A novel study conducted in 2006 (Egli and Bruening) showed that pod removal caused stem maturation to be significantly delayed.
Green Stem Syndrome causes several problems, including tough combining or delayed harvest. This can result in yield loss due to moisture and shattering, a major inconvenience. Yield loss is also attributed to the stress that caused the Green Stem Syndrome. During harvest the moisture from the stems can transfer to the seed, so additional care is needed for storage.
The best defense against Green Stem Syndrome is to eliminate or reduce as many stress factor as possible. Good variety placement, adequate fertility programs, and good disease and insect management are all key factors to maintaining a healthy plant.
Let’s hope you aren’t plagued with this late season problem during harvest. Good luck with a safe and productive harvest!