Late yesterday afternoon, I received a phone call from Floyd Co. Extension Agent, Keith Mickler, about green stem in soybean (Figure 1.) I can tell you from personal experience that green stem can cause major headaches when combining soybeans. In fact, it took 6 man hours to clean out my small-plot combine last year after it got stopped up with green stemmed beans! (knife, machete, long screwdriver, torch, lots of sweat equity)
A few things to know about green stem:
1) Green stem is a term used to describe abnormal or delayed maturation in soybeans where the stems and/or leaves of affected plants stay green even after pods reach physiological maturity.
2) Any factor that reduces seed pod development and seed set can lead to green stem.
3) Natural senescence of soybean requires a strong draw of nutrients from the vegetative portion of the plant (source) to the developing seed (sink). When sink tissue is reduced, protein and sugars are retained in the source tissue resulting in green stems.
4) Seasonal environment stresses (water, temperature, hailstorms, animal damage, excessive soil nitrogen availability at R6-R7), certain viruses (Bean pod mottle virus, Tobacco ringspot virus and Alfalfa mosaic virus), insects (stinkbugs, common brown leafhopper, bean leaf beetle), soybean genetics (cultivars), and fungicides (especially strobilurims) are considered to be causal agents and risk factors associated with green stem.
5) Harvest aids or desiccants such as Gramoxone (paraquat) or Defol (sodium chlorate) have had some effect on green stem but are often inconsistent. Recent research showed that desiccants reduced green stem about 50% of the time. Defol 5 applied at R7 reduced green stem by 38.3%-50.9% compared to the NTC with short (0.5-1.0 point shorter than normal) and normal maturity groups but not in long (0.5-1.0 longer than normal) maturity groups. (FYI, I have never sprayed a single drop of Defol in my entire career.)
6) Combine operators will need to reduce speed when harvesting soybean fields with green stem.
7) Green stem can resolve itself after a hard freeze.
8) Current soybean harvest-aid/desiccant recommendations can be found on pages 265-266 of the 2025 UGA Pest Control Handbook.
https://fieldreport.caes.uga.edu/wp-content/uploads/2025/08/SB-28-28_3.pdf
Information Sources (recently published in 2025):
Geiss et al. Understanding green stem in soybeans. Crop, Forage & Turfgrass Management. 2025;11:e70065 (https://acsess.onlinelibrary.wiley.com/doi/epdf/10.1002/cft2.70065)
Kendall et al. Harvest aid applied at soybean growth stage R7 rarely impacted seed, protein, or oil yield. Agronomy Journal. 2025;117:e70109 (https://acsess.onlinelibrary.wiley.com/doi/epdf/10.1002/agj2.70109)