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Sample for SCN before picking out 2013 seed

Posted Tuesday, October 23, 2012, at 1:06 PM

Soybean cyst nematodes (SCN) are fairly common in this area. A lot of acres are planted to SCN resistant soybeans but not all acres. Sampling for the presence of SCN can provide additional options for selecting soybean varieties for next year.

First, if you have not been growing SCN resistant lines, you need to check for the presence of SCN nematodes.

Nematodes can be moved into a field through flood water, machinery movement and even wind. Nematodes are microscopic worm-shaped animals that are virtually invisible to the naked eye and can survive in soil for multiple years in the absence of a plant host.

If you are sampling for the first time, the most likely areas to find the nematode are previously flooded area, high pH areas, along fence rows, field entryways, low spots, and consistently low-yielding areas.

The second area of concern is if you have been planting SCN lines for a while to control a known nematode infestation. The common source of SCN resistance is PI88788. This source is used in over 95 percent of the SCN resistant lines.

Continued use over a long period of time has led to increases in the build-up of SCN populations in the soil. There are about 16 races of nematodes and PI88788 control only 2 or 3 races. By using the same source of SCN resistant year after year, population shifts will occur and the nematode populations will increase. If you have been using PI88788 as the source for resistance, soil sampling for nematodes is recommended after three or four soybean crops.

Samples should be taken when the soil is moist -- not when the soil is too wet or too dry, and right after harvest in the fall is the best time.

To adequately sample for nematodes a one inch diameter soil probe is best. Collect 8 inch long cores beneath the previous crop row or root area.

Collect 15 to 20 soils for a limited sampling area of 20 acres or so. A uniform random sample will provide the best results. The soil ores from each sample area should be mixed thoroughly and then place about one quart in a zippered bag and labeled with a permanent marker.

Samples should be stored in a cool, dark place until shipping to a nematode lab. More information on the nematode lab is located at: http://soiltestlab.missouri.edu/nematode... or you can call the lab at 573-884-9118.

By knowing if you do or do not have nematodes and what levels you have them, should allow you to make better selections for varieties in 2013.

You may be passing up some varieties that do not have SCN resistance, when because of no or low nematode populations, you could be using. On the flip side, you may not be using SCN varieties where they could provide you a yield enhancement.

Knowing more about your field conditions will allow you to make more informed choices.

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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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