Agronomy Talk

AGRONOMY TALK: SOYBEAN CYST NEMATODE (SCN)

Published on Friday, April 10, 2020

Soybean cyst nematode (SCN) in the United States was first observed in 1954 in North Carolina, and it has continued to spread throughout most of the major soybean growing areas (Tylka and Marett 2014). It is the most damaging pest in soybeans by a large margin. Soon after SCN was discovered in the U.S., SCN-resistant germplasm sources were developed and, over the years, have increasingly been incorporated into the soybean breeding programs across the industry. By the 1990s, most soybean variety releases contained SCN resistance. Industrywide, over 90% of all new soybean varieties include SCN resistance. There are many sources of genetic SCN resistance, but the PI88788 source of resistance is widely adopted. Many SCN populations have evolved tolerance to the PI88788 source of resistance. Peking is another popular source of genetic resistance that remains effective in PI88788-tolerant populations.

SOYBEAN CYST NEMATODE PRESENCE AND SYMPTOMOLOGY:

In many fields across the U.S., SCN is present, but the symptoms are subtle or not visible at all. In areas within fields with larger populations, the symptoms can include yellowing and stunting of the soybean plants. However, significant yield impact from SCN can happen in the absence of visual above-ground symptoms. In addition to direct yield loss, SCN damage can lead to the earlier development and increased incidence of critical soilborne diseases like sudden death syndrome and brown stem rot. 

SCN SOIL SAMPLING:

Fall soil sampling is most effective to detect SCN. SCN do not travel very far and populations tend to be distributed sporadically throughout a field. Break the field into 20-acre zones. Sample suspected hot spots as a separate zone. Take 10-20 soil cores from each sampling zone; sample up to 8 inches deep and stay along the row to be sure that the sample is from the root zone. Mix the samples well before submitting to a reputable lab for analysis. Be sure to put nematode samples in a plastic, not paper bag.

SCN SCOUTING:

  1. Soil sample in the fall to evaluate SCN populations
  2.  Scout in-season for yellowing or stunting from SCN
  3. Dig plants during the summer to see if there is evidence of cysts on soybean roots 

SCN MANAGEMENT

Once SCN is present in a field, it’s nearly impossible to eradicate the pest. It’s critical to avoid moving the pest from infected areas to unaffected fields. Cleaning equipment before entering fields with no known SCN pressure is an important step.

1. Rotate to nonhost crops and keep weed pressure low, especially weeds that are SCN hosts. If fields have severe SCN populations that make soybeans not economically viable, use multiple years of nonhost crops before growing soybeans again. 

SCN ROTATION CONSIDERATIONS

 

NON-HOST PLANTS HOST PLANTS
Alfalfa, Barley, Canola, Corn,
Cotton, Wheat
All Soybeans, Chickweed, Henbit, Peas, Pokeweed,
Purslane, Vetch, Many Others

 

2. Plant varieties with genetic resistance to SCN; try to incorporate soybean varieties that have the Peking source of SCN resistance.

3. Use seed treatments that contain nematode control Soybean cyst nematodes have spread and now encompass much of the soybean growing area, making it extremely important to take soil tests to understand SCN egg counts. If SCN populations are present in a field, the incorporation of management practices to reduce SCN populations are critical to maintaining soybean productivity. 

 

 

Allen, T. W., et. al (2017). Soybean Yield Loss Estimates Due to Disease in the United States and Ontario, Canada, from 2010 to 2014. Plant Health Progress. 2017, 18, 19-27.

Tylka and Marett, 2014. “Distribution of the Soybean Cyst Nematode, Heterodera glycines, in the United States and Canada: 1954 to 2014.” Plant Health Progress 15(2):85-87. https://www.plantpath.iastate.edu/scn/management-scn

Wrather and Mitchum, Revised August 2010. “G4450 Soybean Cyst Nematode: Diagnosis and Management.” University of Missouri Extension. Retrieved March 23,2020 http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.aspx?P=G4450. 

 

 

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Author: Pat Holloway

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