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Soybean Cyst Nematode Distribution in North Dakota (05/21/20)

Between 2013 and 2019, over 4,000 SCN soil samples have been submitted by North Dakota growers using the Soybean Cyst Nematode (SCN) sampling program operated by NDSU Extension.

Between 2013 and 2019, over 4,000 SCN soil samples have been submitted by North Dakota growers using the Soybean Cyst Nematode (SCN) sampling program operated by NDSU Extension. The North Dakota Soybean Council has financially supported the SCN sampling program by covering the cost of the laboratory fees when growers used pre-marked bags, which are available at the County Extension Offices in the fall.  We thank the NDSC for their support.

 

What is SCN?

 

SCN is a nematode, a microscopic worm, that feeds and reproduces on root tissue. The two crop hosts in our region are soybeans and dry beans, but several weeds can also be SCN hosts. Once a female worm infects the root and begin producing eggs, their body expands into a lemon-shaped structure called a cyst. Each female can produce a couple hundred eggs, and the life cycle can repeat 2 to 3 times in a growing season.

 

SCN is the top yield-robbing pest of soybeans in the US, causing over $1B in losses every year to the national soybean crop. SCN is notorious for causing yield loss before above-ground symptoms appear, making it difficult to detect. Consequently, soil sampling is the best way to detect SCN.

 

Where is SCN in ND?

Results of the statewide sampling program indicate the SCN is common in soybean fields in the SE part of the state (Figure 1 and 2). Although it occurs in many additional counties, SCN is generally less frequently identified and in lower numbers.

markell.1

markell.2

How do I interpret the numbers?

 

When growers submit a soil sample for assessment of SCN to a laboratory, scientists microscopically evaluate the soil for nematode eggs, and present that number as eggs/100 cc soil (basically, how many eggs occur in about 3.3 ounces of soil). It’s an imperfect science (there can be false negatives and positives both), so interpretation of results are important.

 

In our maps:

  • Black circles are negatives. It doesn’t mean you don’t have SCN for sure, but no eggs were found in a sample.
  • Gray boxes (50-200 eggs/100cc) are very low levels, which could be real, or could be false positives (other nematodes produce eggs in soil too). I often suggest these are ‘inconclusive’, but it is critical you sample for SCN in the future.
  • Green triangles (200-2,000 eggs/100cc) are low-level positives.
  • Blue circles (2,001-10,000 eggs/100cc) are positives.
  • Yellow squares (10,000-20,000 eggs/100cc) indicate high levels of SCN.
  • Red pentagons (20,000+ eggs/100cc) are extremely high levels of SCN.

 

Yield loss becomes more likely as your egg levels increase, but it is notable that yield loss is possible at any level of SCN. Why? First, SCN can reproduce very fast and your numbers can go from 1,000 eggs/cc to 30,000 eggs/cc on a susceptible variety when the environment is favorable. Second, SCN is notoriously variable in fields and farms, and you will have both lower and higher spots in your field. The take home message? If you have SCN at any level, it is very important to manage it.

 

What can I do?

 

If you don’t know if you have SCN, sampling for SCN is the first and most important step towards management. This can be done in the spring (see the press release from The SCN Coalition) or most commonly in the fall. The NDSC and NDSU Extension are again supporting the SCN sampling program this fall, and more information will be available in future Crop&Pest Reports.

If you know you have SCN, spring sampling, followed again by fall sampling, can be a great way to determine if your management tools are working.

The management decisions for SCN are made before planting. However, crop rotation, genetic resistance and seed treatments are available for future seasons. For more information, visit www.thescncoalition.com and be on the lookout for more SCN information in future Crop&Pest Reports.

 

 

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

 

Guiping Yan

Plant Nematologist

 

Berlin Nelson

Soybean Pathologist

 

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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