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Fall is optimal time to test for SCN, analysts say

Agriculture.com Staff 10/06/2008 @ 7:15am

Last year, soybean cyst nematodes (SCN) robbed farmers in Nebraska alone of more than $25 million in lost soybean yields. This is more than from all other soybean diseases combined.

The problem with SCN is that, unlike other soybean pests, it can cut yield without having any visible symptoms, according to a report from University of Nebraska Extension. Yields may be reduced 20% to 30% on healthy looking plants. If symptoms from SCN were visible during the growing season, you already have a severe infestation which may require you to change your rotation to bring the population down to a manageable level.

You need to identify SCN in your fields and start managing it before damage becomes this severe. The only way to do that at this time of year is with a soil test. You can test for SCN any time (yes, I've done it when the ground is frozen), but in the fall after harvest is best for several reasons:

  1. Poor yielding areas are fresh in your mind. Whole fields or field areas with lower yields that can't be explained by soil type, flooding, weed pressure, or other factors 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.
  2. It's easy to get around in your field to collect soil samples. Take 25 to 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. A sample six to eight inches deep is adequate. Take your sample 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 present.
  3. You can sample fields going into soybeans in 2009 and order SCN-resistant seed, if necessary. If you detect SCN this fall, you can still adjust your seed order. 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.
  4. Farm activity is usually slower after harvest, allowing time to take soil samples. This could be the most valuable time you spend in your fields all year if you look at the potential return. With crop prices where they are today, you can't afford to lose yield unnecessarily. That's what's happening if you have SCN and don't manage it.

Last year, soybean cyst nematodes (SCN) robbed farmers in Nebraska alone of more than $25 million in lost soybean yields. This is more than from all other soybean diseases combined.

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