Oct. 27, 2014

$45 million.

That's how much Nebraska soybean farmers are estimated to have lost to soybean cyst nematodes (SCN) last year.

The good news is that loss will decrease in 2014. The bad news is that's because the price of soybeans is lower, not because SCN is any less common.

SCN is a microscopic roundworm that attacks the soybean root and can have a devastating effect on yields.

SCN is the state's leading nemesis to achieving top soybean yields. It has been identified in 56 counties that produce over 90% of Nebraska's soybeans. If you totaled the yield losses of all other soybean diseases in Nebraska, the number would be much less than the damage from SCN alone.

Related losses can occur from two diseases on the increase in Nebraska soybean fields: sudden death syndrome (SDS) and brown stem rot (BSR). A field can have either of these diseases without having SCN or it can have SCN without having either of these diseases, but if a field has SCN in a field or even part of a field, it is more likely to have SDS or BSR in those areas of the field where SCN is present.

What makes SCN such a problem is yields can be reduced 20 to 30 percent with no visual signs on the plant. Plants can appear normal and healthy, but suffer significant yield losses. In fact, often the first indication of an SCN infestation is a soybean yield that seems to hit a plateau or even start decreasing while corn yield in the field continues to increase.

If SCN caused lesions, distorted growth, holes in the leaves, or some other plant abnormality, it would be much easier to convince people to check for it; however, it is microscopic most of its life and doesn't produce distinct signs on the aboveground plant.

There is only one time during SCN's 25-30-day life cycle that it is visible: when the cyst or female is swollen with several hundred eggs and can be seen on the outside of the root. These cysts are very small, much smaller than a Rhizobia nodule, and lighter in color during the growing season. As plants mature, the cysts turn darker and become even more difficult to see.

Testing for SCN This Fall

The best way to determine if you have a problem with SCN is to take a soil test. (See SCN Sampling is Part Science, Part Art.)  If you discover SCN in your field, switch to a resistant variety the next time you plant soybean.

Unlike other nematodes, you can test for SCN year-round; however, most samples are taken after harvest for several good reasons:

• This is generally a time of year when other farm activities are not as demanding.
   
• This is typically when soil samples are taken for the following year's fertilizer recommendations. You can take a few more soil probe cores from a field, mix them together, then split the sample and send in half for your fertilizer recommendations and half for an SCN analysis.
   
• Poor yielding soybean fields, or even areas within a field, are fresh in your mind and can help you identify fields or areas you want to sample. Yield maps can be very helpful.
   
• If sampling a soybean field, pull your samples a couple inches to the side of the old soybean row. This way you are sampling through the root system and you are more likely to detect SCN if it is there.
   
• If you are sampling a corn field or other crop residues that will be going to soybeans next year, just take random samples. The advantage of doing this is, if you detect SCN in your fields, you can select varieties resistant to SCN.

Free Sample Analysis

The Nebraska Soybean Board has provided funding for SCN soil analyses since 2005 for Nebraska farmers, field scouts, and others. This is a great way to get a return on your checkoff dollars for your farm. Contact your local UNL Extension office for the bags for your free soil analysis, a service that would usually cost about $25.

Expanded Benefits to Controlling SCN

In the past eight years, 29 UNL Extension research trials have shown an average six bu/ac yield advantage for SCN-resistant varieties in SCN-infested field when compared to top yielding susceptible varieties. Besides increasing yields, resistant varieties reduce SCN reproduction while susceptible varieties allow SCN levels to increase, sometimes dramatically. A lower SCN density in the soil reduces the direct negative impact from nematodes feeding on the plant as well as reducing the incidence of sudden death syndrome (SDS) or several other soybean diseases.

Don't contribute to the losses that Nebraska soybean farmers experience from SCN. Sample your fields for SCN and manage your fields if you do find it. Interested in increasing your soybean yields? The answer is in the bag.

Resources

To get you bags for a free SCN analysis or for more information on checking your fields for SCN, contact your local UNL Extension office (see online Extension Directory). 

For more information, see

• Soybean Cyst Nematode page in CropWatch Plant Disease Management section
• SCN Sampling is Part Science, Part Art

John WIlson
Extension Educator, Burt County
Loren Giesler
Extension Plant Pathologist