The words green stem syndrome should shoot shivers down your spine. Generally, most producers have experienced this phenomenon where the soybean plant is fully mature but the stem of the plant remains green, making combining difficult. So, what exactly is green stem syndrome?
Green stem syndrome (GSS) is a soybean disorder in which the main stem of the plant remains green after pods and seeds are fully mature. In some cases, leaves can remain attached to the upper nodes of the plant. Last year in the Effingham area, farmers experienced some of the worst GSS I have ever seen.
Generally, combine speeds were reduce by over 50 percent. When we experience this issue, harvest will take longer and can reduce overall grain quality due to the lack of moisture in the grain when harvested. So, what is the exact cause of green stem syndrome and how can we fix it?
The exact cause of green stem syndrome is still unknown. Theories have suggested viruses (bean pod mottle virus), bean leaf beetles and Cercospora leaf blight. However, research has shown no connection between green stem syndrome and many of these causes. This doesn’t essentially mean these elements do not cause green stem syndrome, but what is obvious is that you can get GSS minus these factors. There is some work being done with stink bugs and GSS and a possible relationship between the two.
Additionally, environmental concerns such as compaction, water stress, potassium deficiency and an acid pH have also been considered as possible factors. While none of these have been shown to cause GSS consistently, typically these factors limit pod or grain numbers at the end of the season.
Stress experienced early in the season (June-July), followed by optimum conditions in August, creates prime conditions for GSS to occur. During the June-July time frame the plant is trying to determine which flowers and pods to keep and which ones to abort. If we experience stressful conditions then, the plant will compensate and abort a high number of pods. When this is followed by conditions that are optimum for growth, the plant has nowhere to ship the carbohydrates it produces. The plant then has no choice but to store excess carbohydrates in its stem and leaves, delaying plant senescence and death. Overall, these ideas are still theories and have yet to be proven through scientific testing.
So, what can we do for future soybeans crops to combat GSS? Unfortunately, still not much. Crawling through green soybeans while harvesting is not fun with an expensive combine. One choice is to wait until a hard frost or wait until stems dry down. However, this is risky as pods can split or shatter as beans become too dry. Using Gramoxone® to defoliate and dry the plants prematurely can speed the process up, but success has been inconsistent. The most practical option is to harvest at the correct moisture (13 to 14 percent), drive slowly and let the combine do its job. Unfortunately, no management practices now available will help prevent green stem syndrome.
Nick Marley is an agronomist and Certified Crop Adviser. He has a B.S. in agronomy and crop science from the University of Illinois and is working on a Master’s in agronomy and crop science at Iowa State University. He is a 2017 Illinois Soybean Association CCA Soy Envoy.