Soybean cyst nematode (SCN) is the most serious pest of soybean in Kentucky. A survey funded by the Kentucky Soybean Promotion Board in 2006 suggested that most of the SCN populations in Kentucky can now reproduce on Plant Introduction (PI) 88788. This PI is the genetic basis of more than 90 percent of available SCN-resistant soybeans.
Sixty percent of the SCN populations tested from Kentucky could reproduce on PI88788 at a high enough level to impact yields.
SCN is the leading cause of yield loss in United States soybeans by disease. Although SCN-infected soybeans may not appear sick, annual yield losses from SCN exceed 100 million bushels.
Effective management of SCN starts with knowing how many nematodes (SCN egg counts), and what race (SCN HG type) of nematode you have in your fields. You can find that information with SCN soil test. The KSPB is sponsoring free soil tests through the state checkoff for farmers wanting to stay abreast of their SCN situation.
Don Hershman, with the University of Kentucky, provides five simple steps to collecting soil samples:
Step 1 — Time of Sampling
Sample fields anytime from mid-September through late March. Sampling during this period provides the best opportunity for assessing the SCN situation. It is best and easiest to sample fields when the soil is damp but not wet. We can process soil in almost any condition. However, your ability to collect a “good” sample may be compromised when attempting to sample very wet or very dry soil.
Step 2 — Sample Size and Representation
The results of an SCN analysis are only as good as the soil sample sent to us. For statistical reasons, samples should not represent more than five acres, and they should be of the same soil type and cropping history. For each five-acre area, or if you elect to have the sample represent a larger area, the critical point is to have the entire area represented in the sample. This will require walking the entire sample area. For example, do not sample only from a two-acre area if the sample is to represent five acres. In addition, you may include areas of a field which historically show poor growth or yield poorly, but do not allow an entire sample to be comprised of such areas.
Step 3 — Collecting the Sample
For each sampling area, use a soil probe or small spade to collect soil, six to eight-inches deep, from at least 20 locations (i.e., 20 sub-samples) throughout the area. Follow a systematic zigzag pattern when sampling. The number of steps between each of the 20 sub-samples will depend on the size of the area being sampled, but remember to walk the entire area. Collect the sub-samples in a bucket as you proceed. For fields currently in soybeans, collect sub-samples from the root zones of plants. The same is true for fields of harvested soybeans where the rows are still visible. If the area to be sampled is in some other crop, or has been disked or plowed, sub-samples can be taken from any location in the field, without regard to rows or root zones. Once the 20 sub-samples have been collected, thoroughly mix the contents in the bucket and immediately place two pints in a plastic bag. Mark the field name and/or number on the bag and place it in a sturdy container for later shipment to the SCN Laboratory.
Step 4 — Handling and Mailing Sample
Protect the sample from extreme heat and/or excessive drying. Take the sample to your local County Extension Office for mailing. If this cannot be done on the same day in which the sample was taken, store the sample in the shade or an insulated cooler. Any prolonged storage should be done at refrigerator temperatures — do not freeze. Be certain to include a complete SCN Analysis Form for EACH soil sample submitted to the SCN Laboratory. (The analysis form may be printed from http://www.kysoy.org/ or by calling the soybean office 800-232-6769).
Step 5 — Results and Recommendations
Once received by the SCN Laboratory, your sample will be processed and results and recommendations sent to you at the address indicated on the SCN Analysis Form. Remember the results and recommendations you receive from the Laboratory are directly related to the quality of the sample you send to us. Samples submitted that are not representative of the field situation, samples not submitted during the recommended time frame, or samples handled improperly may yield misleading and/or erroneous results.
For more information and sampling forms visit: http://kysoy.org/news/scn%20testing.htm