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jschwartz@icorn.com
October 20, 2003

What in the world happened to soybean yields?  A follow up

After my e-mail on low soybean yields went out last week, a few folks have sent in some additional thoughts about other factors that might have contributed to the low yields.  The first one listed below is from Dr. Pat Lipps, a plant pathologist from the Ohio State University.  I have a tremendous amount of respect for Pat and his knowledge of "real field occurrences".  In other words, he gets dirty to find the answers.  Especially take note of his comments on the location of active nodules on the root system.  I have included his e-mail response to me for you to look over.  His comments would be especially relevant for Ohio and Indiana.

Jim,

Thanks for sending your article via email to us. I could not help but make a few comments about your views concerning the poor soybean yields in Ohio.  I generally agree with your statements but I feel you have not taken into account some of the true causes of poor yield.  

I agree with the impact of temperature and high moisture conditions and their effect on Rhizobium.  In fact we looked at a lot of soybean roots from a week after planting all the way through harvest from fields throughout Ohio.  It was obvious that the Rhizobium nodules were positioned on the roots nearest the soil surface and few to no nodules were present on lower roots.  Thus the overall level of nodules was much less than normal.  Secondly, severe root diseases occurred throughout the state due to the protracted saturated soil conditions.  This was in addition to the flooding injury to the plants.  The roots were rotted due to activity of a number of pathogens including Phytophthora, Pythium, Fusarium and Rhizoctonia.  Because of the extensive root colonization it was very difficult to determine which pathogen was causing most of the problem.  2003 was one of the worst years I have seen for the widespread level of root rots.  During grain development it was probably very lucky we received continued rains that allowed the sickly root systems to continue to take up moisture.  Had the weather turned off dry, I believe most of Ohio's soybean crop would have died prematurely from root rots.  The stress applied by the soybean aphid, poor nodule development and root diseases were the main cause of the poor yield and of course at least two of these factors were enhanced buy the weather conditions.  In a year with more normal rainfall conditions and less root rot, the soybean plants could probably stand relatively high aphid pressure with less yield impact.

Just some of my thoughts and observations to add to yours.

Best regards,

Pat Lipps

Jim--

I have some very strong thoughts on this, and none are covered by your recent email on the topic!

I think the aphids played a role in stressing soybeans, but the main culprit was clearly Charcoal Rot.

I was surprised to see so much of it in Indiana and Illinois, and it was devastating throughout Iowa, Missouri, Kansas, Nebraska, Minnesota, and even North into the Dakotas, Michigan, and Wisconsin.

I really did not tour Ohio, so not sure about that. 

The best evidence is this:  Clouds of dust billowing out of every combine at harvest time.  One of the effects of charcoal rot is how it causes the dead leaves to hang on the plant.  When you combine the beans they just turn into a cloud of dust.....

See the recent report from U. of Illinois http://www.ag.uiuc.edu/cespubs/pest/articles/200323g.html

I think they are right on the money
Make any sense?

Mike

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