Scouting for soybean cyst nematode (SCN) is checking to see if your soybean field is infested with SCN, or if your SCN–resistant soybean variety is suppressing SCN reproduction in your field. This activity can be performed starting from 6 weeks of planting to 4 weeks before harvest. During this period, if present, SCN will be actively feeding and reproducing on soybean roots. So they can be easily seen.
To do the scouting, use a shovel to dig up stunted or yellowish soybean plants, digging from 6 to 8 inches away from the plants to ensure digging out both the roots and the soils attached to them, making sure the roots are not cut by the shovel into the soil.
Please note that pulling out soybean plants with your hands would not work when scouting for SCN. Doing this would make most of the roots lost in the ground, and you may find little to no SCN female on the roots since they are withdrawn into the soil in the process of pulling.
After digging out the plant, gently remove excess soils from the roots, using your thumb and the four fingers to very gently rub off the soils. Then check the exposed roots for the presence of adult SCN females, appearing like a white dot on the roots. Using a hand lens or magnifying glass would reveal them more clearly – appearing in white or yellow color and lemon shaped. They are a little bit smaller in size than soybean root nodules. You would see many of them on susceptible soybean cultivars, but they should be few, not more than 20, on resistant variety.
For a more successful SCN scouting, scout for SCN near field entrance, areas prone to flood and high pH, low areas, areas with yellow or stunted plants, and along fence lines. Also, healthy soybean plants should be scouted too, as soybean plants may be infected with SCN and have no symptom. The only symptom would be observed as low yield at harvest.
For more information on this topic, see Scouting for SCN in yellow or stunted soybeans by Greg Tylka, visit UTcrops.com and Cropprotectionnetwork.org for more info on soybean diseases.