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Corn+Soybean Digest

Soil Testing Diffuses Soybean Time Bomb

SCN is like a time bomb in the soil waiting to explode.

That's how Ann MacGuidwin describes this yield-robbing, microscopic pest.

MacGuidwin, a University of Wisconsin nematologist, says it's important that every grower diffuse the bomb by having soil tested for SCN and then using recommended practices to control the pests.MacGuidwin recommends that gr owers test regularly for SCN.

Negative test results can ease growers' minds, but are not a guarantee there won't be future problems.

She advises sampling in the fall before every other soybean crop, although samples can be accurately analyzed at any time during the year.

Guidelines for collecting soil samples:

1) Limit the number of acres represented in a single sample. Usually 10-20 acres is ideal. If the field is bigger than that, break it into 10- to 20-acre units.

2) Collect 10-20 soil cores from each field or unit using a probe, hand trowel or shovel. The intensity of sampling depends on the information at hand. If there are problem spots that show up year after year, then sampling efforts can be limited to that area. When there are no obvious symptoms, use the 10-20 cores approach.

In any case, its never a good idea to take fewer than five soil cores because the sample will not be very representative of the field. The more spots you sample, the better.

* Take samples from a depth of 6-8" in the plant root zone.

* Combine the soil in a bucket and mix well. A composite sample mixed well will represent the area better.

* Place 1 pint of soil in a plastic bag or paper soil-test bag.

* Keep samples out of the sun and ship them ASAP to a university or private soil lab. Cost ranges from $5 to $24, but some state checkoff boards cover processing costs.

3) Include the following when submitting your samples:

* Name, address and telephone number of farmer or sample collector.

* County and nearest town where samples were collected.

* Estimated acreage of areas sampled.

* Cropping history of areas sampled.

* Current crops of areas sampled.

Each test will give an estimate of SCN population density based on the volume of soil. The standard volume used is 100 cubic centimeters (cc) of soil.

Most labs report the number of SCN eggs, but some give the number of cysts. Cyst and egg counts are not directly comparable. A low cyst count does not equal a low egg count, since each cyst can contain hundreds of eggs.

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