November 4, 2010

Now, as harvest winds down and before the ground freezes, is an excellent time to check your fields for soybean cyst nematodes (SCN). The time you take now to sample for SCN could make a big difference in your bottom line next year.

Last year SCN cost Nebraska farmers over $25 million in lost soybean yields. This is more than the estimated losses from all other soybean diseases combined.

If you have SCN, but aren't managing the problem, you share in that loss. How much depends on how many acres of soybeans you raise and, if present, how severe the SCN infestations are in your fields.

The problem with SCN is that, unlike other soybean pests, there may be no visible symptoms. Yields may be reduced 20-30% on healthy looking plants.

If SCN symptoms were visible in a field last summer, you already have a severe infestation which may require you to change your rotation to bring the population down to manageable levels.

You need to identify SCN in your fields and start managing it before it causes severe damage. While you can test for SCN any time, it's best to sample in the fall after harvest for several reasons.

Benefits of Fall SCN Sampling

• First, poor yielding areas or fields are fresh in your mind. Areas with lower yields that can't be explained by soil type, flooding, weed pressure, or any of the other things that can reduce soybean yields are commonly caused by SCN. This is especially true if the same areas have good corn yields, but poor soybean yields. Concentrate your soil sampling in these areas.
   
• Second, after harvest it's easy to move around in fields to collect soil samples. Take 25-30 soil cores and mix them thoroughly, then pull your sample from this soil. If you normally test your fields for fertilizer recommendations in the fall, take a few more core samples and then split the sample -- half for fertility analysis and half for SCN analysis. For SCN, take samples that are 6-8 inches deep and a couple inches to the side of the old row. That way you go through the root system and are more likely to detect SCN if it is present.
   
• Third, you can sample fields that were in corn or another crop and will be planted to soybeans in 2011. If you detect SCN, you can adjust your seed order accordingly. Resistant varieties and crop rotation are the two main components to managing SCN. Unlike other traits for resistance to herbicides or insects, there is no tech fee for SCN resistance. SCN-resistant varieties don't cost any more than susceptible varieties and our trials show they yield just as well.
   
• Fourth, usually farm activity is a little slower after harvest and before the first snow falls and you'll have time to take soil samples. This could be the most valuable time you spend in your fields all year, or at least it could pay you the biggest return.

With crop prices where they are today, you can't afford to lose yield unnecessarily. If you don't sample for SCN and treat it when found, you're just giving up potential income.

Soybean Board Funding for SCN Tests

The Nebraska Soybean Board is providing soil test bags for free SCN analysis. This is normally a $20 test at the University of Nebraska-Lincoln Plant and Pest Diagnostic Clinic. This project, funded by soybean checkoff funds, is an opportunity to get a return on that investment.

Contact your local UNL Extension office to get your bags for SCN analysis and a copy of the NebGuide G1383, Soybean Cyst Nematode Biology and Management.

John Wilson
Extension Educator
Loren Giesler
Extension Plant Pathologist, Lincoln