Beck's Blog

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Agronomy Update

Green Stem of Soybeans

Published on Thursday, October 9, 2014

Every year there are some soybean fields where the stems stay green while the soybeans are mature and at the ideal moisture. Sometimes the leaves fall off the plant and sometimes they remain green and stay on. The one common symptom for most cases (except fungicides and genetics) is that there is not a heavy pod load on the plant. There are numerous factors that can cause a less than ideal pod load. Below are just a few items that may contribute to green stem.

 

                  


Bud Blight or Tobacco Ringspot Virus - I rarely see this disease but have seen it on a few scattered plants this year. Most plants produce little if any seed (depending on the time of infection) and therefore will stay green with the leaves attached. It is thought that thrips are the insect responsible for transmitting this virus. Because the disease is poorly transmitted and the fact it does not produce much seed, it is usually just found on a few scattered plants. The picture below is an example of the soybean pods that have aborted due to bud blight.

 

       


Soybean Mosaic Virus (SMV) - A disease transmitted by insects. SMV is transmitted by aphids. Some varieties are more susceptible to SMV than others, so you may see it more in one field than another. The timing of soybean planting along with when infection occurs can reduce the soybean pod load and therefore yield.

Fungicides - Fungicides may induce green stem by creating more energy (photosynthates) for the plant than what it can use. A study was conducted by the University of Delaware to see if fungicides actually increase green stem. The results revealed Strobilurin fungicides (ie.Headline, Quadris, Aproach, Priaxor, and Stratego) caused greater green stem symptoms than triazole fungicides, but both sets caused greater green stem than the control groups.(New Research on Fungicides and Green Stem Disorder of Soybeans)

Genetics - Some genetics are just prone to higher levels of green stem. I have heard some people claim that these genetics are higher yielders because they stay greener longer and can create larger soybeans. Although this sounds logical, it may or may not be the case. It is true, however, that genetics do differ.

Other possible factors - Drought conditions, late planting, plant populations, and shallow planting depth have also been associated with green stem, although not consistently. These all would make sense, however. Drought conditions cause fewer and smaller seeds, late planting causes fewer nodes and pods, and shallow planting depth causes fewer pods to develop. Both high and low plant populations have been associated with green stem as well.

Unfortunately, not much can be done to prevent green stem from happening. In addition, the only thing that can help with harvest is possibly to use Gramoxone or to wait until a hard freeze, although that is risky given the fact that the soybean pods may shatter.

 

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