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Many soybean fields are showing yellow areas.  It is often caused by soybean cyst nematodes (SCN).  The nematodes used to be just a Southern problem, but they have slowly worked North.  I have seen them devastate the end rows of a test plot in Michigan.

I used a nematode resistant bean last year and am using a different nematode resistant bean this year.  Some universities recommend using a variety with Peking resistance after using a regular cyst resistant bean.  However, I was at a Kruger Seed meeting a couple of weeks ago and they do not recommend using the Peking resistance because they are susceptible to brown stem rot.

The two ways to find SCN are to have a soil test analyzed for SCN, or look for soybean plants that are yellowing prematurely.  Then carefully dig up the roots, brush the soil away and look for small cream colored cysts on the roots.

SCN can also aggravate two other soybean stresses.  Sudden death syndrome (SDS) is often seen first where the soybeans have SCN.  Also, I was talking to a friend of mine in North Dakota about iron chlorosis.  Iron chlorosis is a big problem in the Dakotas and Minnesota because the pH of their soils is naturally high.  We haven't seen iron chlorosis as too much of a problem around here, although, every once in a while we see it where the pH in a field is over about 7.4.  My friend said that they are seeing much worse iron chlorosis problems where they also have SCN.

Iron chlorosis occurs because iron and other micronutrients are not nearly as available at high pHs.  Thus, micronutrients are required on high pH soils.

Now is the time to look for soybean fields that have yellow spots.  There is where you will likely find the soybean cyst nematode.