patchy soybean field John Obermeyer, Purdue University Extension Entomology
VISUAL SYMPTOMS: The patchy appearance in this field was caused by soybean cyst nematodes, which can cause yield loss without showing visual symptoms.

Develop approach to control SCN

New tools help, but conquering soybean cyst nematode requires several steps.

Unless you farm in sandy soils and know you have a soybean cyst nematode problem, this hidden threat could be one of the factors preventing you from taking soybean yields to a higher level. Chad Threewits says the first step is to sample and see if you have SCN.

The next step is figuring out what you can do to manage SCN if you have them, says Threewits, an agronomic service representative for Syngenta based in Indiana. In the second half of this exclusive interview with Indiana Prairie Farmer, he points out things you can do over time.

Here are Threewits’ answers to questions about managing soybean cyst nematodes.

What are the keys to managing cyst nematode? It all comes down to three things: Using an effective seed treatment, planting soybeans with the best genetics for resistance possible and crop rotation. You aren’t going to work out of a soybean cyst nematode problem by just doing one thing in one year.

How do you know if you need a seed treatment? We are advising farmers to sample for cyst nematodes, even if they farm heavy, poorly drained soils. Soybean cyst nematodes have been found almost everywhere in Indiana. If you test and the lab determines you have soybean cyst nematodes, then consider a seed treatment.

We offer Clariva, and now we offer Clariva Elite Bean, which was just approved by EPA. It’s a premium seed treatment which includes Clariva as part of the package, along with insecticides and fungicides. (Editor’s note: Other companies also offer seed treatment options for soybean cyst nematode control.)

How does Clariva control soybean cyst nematodes? It’s a biological product. Syngenta concentrated bacteria that have been naturally existing for a long time. They attack and kill nematodes. If you take a sample for nematode counts in the spring and then one in the fall after Clariva was applied, counts will likely go down. However, since Clariva is a biological product, it doesn’t last forever. Counts could go back up later. You should reapply it each year.

What can you tell us about genetic resistance to soybean cyst nematode? It’s important to select a soybean variety with soybean cyst nematode resistance if you know you have soybean cyst nematodes in the field. The issue right now is that about 95% of the varieties with resistance are using the same type of nematode resistance. As a result, some aren’t as effective as they once were. Both company and university researchers are looking for new forms of resistance. But if you have a cyst nematode problem, you definitely still need to make sure you plant a soybean with cyst nematode resistance.

Where does crop rotation play into this scenario? One way to slow down soybean cyst nematodes from building populations is to plant a nonhost corp. Corn is a nonhost crop for soybean cyst nematode, so planting corn in rotation helps. If you plant soybeans after soybeans most years and you have cyst nematodes, the population will continue to grow.

Is there a connection between sudden death syndrome and cyst nematode? They are caused by two different things. However, nine times out of 10, when I see SDS, there is also cyst nematode in the field. Researchers believe that cyst nematodes make infection sites which allow SDS to invade. You can see SDS where there are no nematodes, but usually there is a connection.  

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