Soybean Cyst Nematodes: Do you have a problem?
By Randy Simonson, Technical Services Manager
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.