Plant Disease: Common Soybean Diseases

Soybean Cyst Nematode (SCN)

Common Soybean Diseases Soybean Cyst Nematode (SCN) Soybean cyst nematode (SCN), Heterodera glycinesis the #1 disease of soybean throughout the US. SCN has been confirmed in 58 counties in eastern and central Nebraska (Figure 71).

Distribution of Soybean Cyst Nematode in Nebraska as of January 2016.
Figure 71. Distribution of Soybean Cyst Nematode in Nebraska as of January 2016.
Stunting of soybean due to severe soybean cyst nematode infection.
Figure 72. Stunting of soybean due to severe soybean cyst nematode infection.

Identification of SCN can occur according to field symptoms and/or plant symptoms. For field symptoms the first indication is below-expectation yields. In many cases throughout Nebraska, there are no visible, above ground symptoms of infection yet yields may be reduced 5 to 10 bu/acre or more. With light-to-moderate SCN infestation occasionally a slight variation in height can be observed. As infestation levels become higher symptoms can include stunting, chlorosis, and even plant death. Circular-to oval-shaped areas of stunted, yellow plants can be observed (Figure 72). Infested areas can often be elongated in the direction of tillage practices, since cysts are spread by tillage equipment.

On individual plants, symptoms include stunted roots with fewer nitrogen-fixing nodules on the roots. The unique symptom or “sign” of SCN is the presence of the adult females (also known as cysts on the roots (Figure 73) .Adult females appear as lemon-shaped bodies on the roots and are initially cream-colored. As the female matures, she will turn yellow and finally tan to brown in color. Although the cysts are much smaller than nitrogen nodules, they can be seen with the unaided but trained eye (Figure 74).

Adult soybean cyst nematodes females emerging from soybean roots.
Figure 73. Adult soybean cyst nematodes females emerging from soybean roots.
Comparison of adult soybean cyst nematodes (small white/yellowish structures) to a soybean nodule (brown structure).
Figure 74. Comparison of adult soybean cyst nematodes (small white/yellowish structures) to a soybean nodule (brown structure).

Observation of adult females on the roots is one way to confirm an SCN infestation in field. In general, the females are evident on roots a month after emergence. However, absence of females (cysts) on the roots doesn’t mean a field is free of SCN. When there are low levels of SCN infestations, it is easy not to visualize the adult female on the root. The best way to determine if SCN is present in a field is with a thorough soil test. Figure 75 shows the disease cycle for SCN.

Life cycle of soybean cyst nematode. Photo Courtesy of Iowa State University Extension and Outreach.
Figure 75. Life cycle of soybean cyst nematode. Photo Courtesy of University of California, Davis.

Soybean Cyst Nematode Management

Sanitation:

SCN moves with anything that moves soil including ATV’s, boots, wildlife, equipment, etc. Thoroughly clean equipment when moving from an infested field to a field where SCN has not been identified.

Resistant varieties:

Planting SCN-resistant soybeans is a very efficient management tool. Check with your local seed representative to discuss which cultivars perform the best in your area.

Rotation:

Two types of rotation are needed for successfully management of SCN: (1) rotation between non-host and host crops (Table ___) and (2) rotation in the source of SCN resistance.

Nematicides:

Certain nematicides are labeled for use against SCN, but they are highly toxic and generally not considered economical or effective.

Seed treatment nematicides:

Some nematicides are currently labeled as a seed treatment for management of SCN.

Nebraska Soybean Checkoff

Nebraska Soybean Board graciously provided the funding for the Soybean Management Guide.

Course authored by:

Amy Timmerman, Extension Educator, Aaron Nygren, Extension Educator, Brandy VanDeWalle, Extension Educator, Loren Giesler, Extension Plant Pathologist, Ron Seymour, Extension Educator, Keith Glewen, Extension Educator, Charles Shapiro, Extension Soil Scientist, Amit Jhala, Extension Weed Scientist, Don Treptow, Graduate Student