Soybean cyst nematode resistance key to success in 25 South Dakota counties

 By Ron Dodds
 Extension Educator-Agronomy
Brown County
 ematodes are nearly microscopic non-segment roundworms with a needle like mouth part that allows the nematode to pierce into an animal or plant victim. 
Soybean Cyst Nematodes (SCN) is a type of nematode that parasitizes plants, particularly soybeans and closely related plant species (dry or snap beans, peas, and some forages: sweetclover, vetch, lespedeza, birdsfoot trefoil.  This pest is quite capable of inflicting significant economic harm upon unwary soybean producers.
  SCN first invaded southeast South Dakota in Union County in extreme Southeastern SD in 1998.  Since then it has spread, so that in 2004 it was found in Hutchinson, McCook, Lake, Hanson, Bon Homme, Brown, Deuel, Minnehaha, Yankton, Roberts County, Lincoln, Clay, Moody, Brookings, Hamlin, Grant, Day, and Turner Counties.  In 2008, SCN was also found in Charles Mix, Kingsbury, Codington, and McPherson Counties.
   When a SCN feeds on a soybean root, the physical damage caused by the piercing along significantly interferes with water and nutrient uptake.  The wound site also creates a potential infection site that fungi and bacteria are likely to utilize.  University of Maryland researchers have discovered that SCN infected roots nearly stop developing.
   10 - 30% yield decreases can be detected by yield mapping within fields early in the infestation process.  Unfortunately the affected plants are rarely visible.  Once a producer suspects that there may be pockets of infestation in a field, section or range soil sampling and SCN testing is in order.  In fact, SCN testing in the counties listed above should be routine in fields near infested fields to determine if control and management practices need to be altered.
   One indication that SCN may be present is declining soybean yields in portions or all of a field. Symptoms of SCN often include stunting.  The stunting may be fairly general across the field, but it is more often expressed as a rollercoaster effect.
Additionally, fields infested with SCN often have areas where the plants are slow to close the rows. Infected plants may become yellow in July or August, and they may have reduced vigor or mature earlier than those in surrounding areas of the field.
    Bear in mind that the nematodes can be moved by anything that will move even the smallest particle of soil.  Nematode populations have been known to be as high as 1,000 eggs in less than 1/2 cup of soil.
   How can producers/manage or control this pest?
  The key steps to managing this pest are:
  Till and harvest affected fields last whenever possible.
   Be sure to thoroughly power wash (with soap) equipment that has been in infested fields, especially the tires, tracks, muddy/dusty axels & fenders, boots and shoes.
   Study yield maps carefully for unexplained low yield pockets.  Low yield streaks, on the yield map for recently tilled fields, are often indicators of a SCN infestation.
   Take soil samples for SCN testing from the areas of questionable fields that are most likely to be infested first. SCN tends to be discovered near field entrances and fence lines and in low-lying areas where water tends to accumulate, or in high pH soils.  One SCN-soil sample shouldn't represent more than 20 acres.  Sample kits and specific instructions are available at most CES offices wherever soybeans are grown.
   Use crop rotations with non-host crops such as corn and wheat to keep SCN populations low.
   Resistant varieties often offer 23 - 63% higher yields than do susceptible varieties in SCN infested fields.
Experiment with small plots containing several varieties on your farm to see which two or three works best for you.
There is a new bacterial product, called Votivo® , coming on the market from Bayer Crop Science™for the 2011 planting season.  According to Bayer™, this product is a bacterial product that colonizes soybean roots.  At this time, this educator is unable to locate any university based research regarding this product.  On farm testing may be warranted in the absence of university research.  If this product works the way it is supposed to it may be a valuable tool for an integrated SCN management approach that also incorporates resistant varieties and crop rotation.
   No matter the pest, an integrated approach is always the best.  Single control measures or single modes of action are eventually overcome. 

Soybean Producers can get additional information about Soybean Cyst Nematodes at the following websites:
http://agbiopubs.sdstate.edu /articles/FS902A.pdf (South Dakota Extension Fact Sheet 902-A)
http://www.extension.org/pages/Soybean_Cyst_Nematode_Continues_to_Spread_in_South_Dakota
http://www.umac.org/agriculture/ss/40/detail.html
http://www.omafra.gov.on.ca/english/crops/pub811/p811toc.html (Ontario, Canada)
http://extension.umd.edu/publications/PDFs/fs825.pdf  (Maryland CES)