July 9, 2022
Impact and Significance of Soybean Cyst Nematode
Soybean cyst nematode (SCN) is a common pest in many Midwestern soybean fields and is the number one cause of yield loss in soybean production across the United States. Damage caused by SCN is often hard to identify as visual symptoms may be lacking and can be quite variable.
Identification and Lifecycle
Soybean cyst nematodes are microscopic roundworms that infect soybean roots during their juvenile stage. Like other plant-parasitic nematodes, SCN have three stages: egg, juvenile and adult. After the eggs hatch, juveniles infect soybean roots and begin feeding. Shortly after infection, the juveniles become either males or females. The males leave the roots and stop feeding, while the females continue to feed on the soybean roots and become enlarged, until part of their body breaks out of the root (Figure 1). Female SCN are the primary cause of damage to soybean plants and are referred to as a white female. The females continue to feed and eventually turn into brown cysts, which house up to 500 eggs. The cyst can protect the eggs and persist for years. Soybean root exudates stimulate hatch and start the cycle again.
Figure 1. Female soybean cyst nematodes protruding from soybean roots.
Scouting
White female SCN bodies can sometimes be found protruding from soybean roots around the time the plants are flowering. Aside from visually seeing these adult females on soybean roots, the only other way to identify SCN presence is through soil testing. Soil samples should be taken around soybean harvest when SCN populations are the highest
Visual symptoms of SCN are quite variable, which makes identifying SCN in the field difficult. Symptoms can be confused with herbicide injury, diseases, nutrient deficiencies, and environmental stress (Figure 2).
Figure 2. Soybean cyst nematode symptoms can mimic nutrient deficiencies, soybean foliar diseases, and other crop injuries.
SCN Management
The main goals for SCN management are to increase soybean yield potential, keep SCN numbers low, and to sustainably manage SCN-resistant soybean products. SCN-resistant soybean products are the primary management tool to help reduce infestation levels. These SCN-resistant products do not eliminate SCN reproduction and should be used in conjunction with other management tactics such as crop rotation, effective weed control, and seed treatments. Consider rotating to corn, cotton, wheat, alfalfa, or sorghum to help manage SCN populations. Effectively controlling winter annual weeds is an important management tool because these weeds can serve as hosts for SCN. Using a seed treatment, such as ILeVO® seed treatment, can be beneficial for SCN management.
Sources:
Pederson, P. 2005 Managing soybean cyst nematode. Iowa State University. https://crops.extension.iastate.edu/files/article/SCN_000.pdf
Niblack, T.L. and Tylka, G.L. 2010. Soybean cyst nematode management guide 5th edition. Plant Health Initiative, North Central Soybean Research Program. https://www.soybeanresearchinfo.com/pdf_docs/SCNGuide_5thEd.pdf
Tylka, G.L. 2012. Soybean cyst nematode field guide 2nd edition. CSI 0012. Iowa State University Extension and Outreach.
Web sites verified 5/10/22.
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