Yellow Soybeans: What is the Cause?

July 22, 2009 at 8:00 am

You don’t have to drive too far to see patches, or small areas, within a soybean field that show yellow soybeans.  Here are the typical symptoms:

1. Generally, the areas in the field are small–perhaps a circular area with a diameter ranging from 25′ to >75′

This is a typical yellow area currently observed in some soybean fields.

This is a typical yellow area currently observed in some soybean fields.

2. The uppermost leaves are affected–that is, the symptoms show up only on the newest growth on the soybean plant

The newest growth of soybeans clearly shows the symptomology.

The newest growth of soybeans clearly shows the symptomology.

3. The uppermost leaves have interveinal chlorosis–the veins are green or dark green and the leaf area between the veins is yellow or very light yellow.

Interveinal chlorosis: green veins and yellow leaf tissue.

Interveinal chlorosis: green veins and yellow leaf tissue.

Robert Mullen, Keith Diedrick and Ed Lentz wrote an excellent article in the July 7, 2009 CORN Newsletter providing an overview of yellow soybeans and diagnosis. There are a few things you can do to verify the presence of a nutrient deficiency.  Mullen recommends the following: tissue sampling, soil sampling, and root observation.

  • Tissue sampling: sample the uppermost, fully-expanded trifoliate and discard the petioles (small stem that connects the trifoliate to the main stem). Collect samples from an unaffected area as well as the affected area.
  • Soil sampling: collect corresponding soil samples from the unaffected area and the affected area at a depth of 8″, unless in no-till or severely reduced tillage.  In no-till or very minimum tillage operations, sample the profile at the 0-4″ zone and at the 4-8″ zone.
  • Root observation: By doing a root observation, we are specifically looking for soybean cyst nematode (SCN). These SCN structures will appear as tiny, lemon-shaped objects on the roots that range in color from white, yellow, tan and brown. They are easy to see with slight magnification (a field lens works fine). The cysts are about the size of a pinhead and considerably smaller than nitrogen nodules. You must carefully remove the soil as not to dislodge the SCN structures.

So what to do? In some cases an application of 1-2 qt. per acre of a liquid manganese product can alleviate the visual symptoms.  However, this may not translate in to a positive return on yield.  Research was conducted in 2004 examining this very problem.  Research results are available here: http://farmfocus.osu.edu/Foliar_Mn-Beans-04.pdf

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