Use your shovel to dig up soybean plants.

Gently shake excess soil from the root system.

Check the root system for adult SCN females. They will be a lot smaller than the nitrogen-fixing nodules, about the size of the period at the end of a printed sentence. Click on image to view larger version.

First, determine your purpose for scouting for SCN. Are you sampling...

• to check if SCN is present in a field before planting next year's soybean crop? Collect a soil sample.
• to determine if your SCN management program has been successful in keeping SCN population densities in check? Collect a soil sample.
• to determine if SCN was responsible for poor soybean yields? Collect a soil sample.
• to look for SCN in stunted or yellow soybeans observed in mid-season, OR in fields that are apparantly healthy, but have not yet been checked for SCN? Examine soybean roots.

Examining roots for SCN
You can scout your fields for SCN by digging plants at least six weeks after planting until 3 to 4 weeks before harvest. However, it is easier to observe the nematode on soybean roots early in the season when new roots can be easily dug from the soil.

Use your shovel to dig up yellow and/or stunted soybean plants. Don't pull up a plant - you'll lose too much of the root system and strip off the females as you pull the root system through the soil.

Gently shake excess soil from the root system. Check the root system for adult SCN females. They will be a lot smaller than the nitrogen-fixing nodules, about the size of the period at the end of a printed sentence. They will be white or light yellow and lemon-shaped.

Where to scout
If you are scouting a field that has never been checked for SCN, consider that SCN can be in a field for many years without the tops of the plants becoming yellow or stunted. For this reason, it is a good idea to include healthy-looking plants in your scouting. A good place to start are in areas that have a higher risk for SCN, such as 

• near a field entrance
• areas that have been flooded at one time
• areas of high soil pH (greater than 7)
• areas where weed control isn't quite as good
• areas where the yield seemed to be a little low the last time soybeans were grown
• along fence lines where wind-blown soil accumulates.

Collecting a soil sample for SCN

1. Use a soil probe or narrow-bladed trowel or shovel. Take cores close to plants at a depth of 8 to 10 inches. Discard the upper 2 inches of soil, especially if it is dry. Be sure to include plant roots.
   
2. Submit one sample for a 10-acre field, or for a suspected area within the field.   Sample from plants in the margins of  suspected areas, and not from their centers. Or collect in a zig-zag pattern across the field. Collect from areas of similar soil texture and cropping history. If different crops were grown, or there is markedly different soils within a field, sample separately.
   
3. Take soil and roots from 12 to 20 plants and mix into one sample (1 to 2 pints of soil). Place in a sturdy plastic bag (or soil sample bag), fasten the open end securely, and label accurately with an indelible marker. Keep the samples out of the sun and don't let them dry out.
   
4. Mail as soon as possible, and early in the week to avoid delays in transit. Mail to the Plant Disease Diagnostic Clinic, 1630 Linden Drive, University of Wisconsin-Madison, Madison, WI 53706. The cost of the analysis is $14 per sample. Or consult with your county extension agent about private laboratories that conduct SCN analyses.

Interpreting the results of an SCN soil test
Different laboratories measure the number of juvenile nematodes, the number or cysts and/or the number of eggs in the soil sample. It is important to realize that each of these measures is interpreted in a different way. The UW Plant Disease Clinic reports the number of eggs. They will include information to help you relate sample results to management options. 

A good outline of how SCN soil tests are interpreted can be found in Interpreting SCN Soil Test Results from Iowa State University (printable pdf file).