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Soybean Diseases - How Can I Tell The Difference?

Soybean Diseases - How
can I tell the difference?

Last week we talked about how white mold is causing scattered
plants in fields to wilt and die. Other diseases are causing the same
appearance or showing leaf discoloration, so in this week’s article, we will
sort out the differences so you can make informed decisions for future

How to tell the difference between White Mold, Phytophthora, and
Sudden Death Syndrome (SDS)

This late in the season, white mold and Phytophthora both can have
the same appearance when you are scouting from the pickup truck - scattered
dead plants.


If you examine these dead plants closely, you may have some of
both of these diseases present. I observed this in a field in Ohio this past

Phytophthora: With this disease, you will
notice that the death of the plant travels from the roots on up (see pictures
below). I’m seeing phytophthora emerge after a period of saturated soil, like
we experienced earlier this month. 


Splitting the stem will reveal the following appearance which will help you
differentiate it from other diseases.


White Mold: The two key differences here are
the white mold on the outside of the stem. 


The second is the black sclerotia on the inside of the stem.



Sudden Death Syndrome (SDS)

SDS is best identified by first noticing the foliar symptoms, then
splitting the stem to confirm that it is not brown stem rot which shows very
similar foliar symptoms. SDS causes interveinal chlorosis on the leaves which
eventually turns brown.



Later in the season the leaves will fall off and petioles will
remain attached. 

When you split the stem, the cortex (outer section of stem) may be brownish.
 If the pith is brown, the plant is likely infected by brown stem rot.

For more Agronomic News from Alex Johnson, Beck’s Certified Crop Advisor, please visit his Agronomy Page on

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