Soil samples taken following harvest provide the best estimates of SCN. Check roots during midseason for the presence of females and cysts.
How to sample soil for SCN»
How to check roots for SCN»

SOYBEAN CYST NEMATODE

Key points to know about SCN
  • Many farmers don't know their fields are infested with SCN - you often can't tell SCN is there from looking at the field.

  • The effect of SCN on soybean yield is directly related to the numbers of nematodes feeding on the root system.

  • Observation of adult females and cysts on the roots of soybean plants is the most accurate way to diagnose SCN infestation in the field.

  • Once present in the soil, SCN can never be eliminated. However, the nematode can be managed to minimize SCN reproduction and maximize crop yields.

  • Crop rotation coupled with planting SCN-resistant varieties are the cornerstones for the management of SCN. Non-host crops, such as corn, sorghum, sunflower, and alfalfa can reduce SCN population densities each year a non-host crop is planted.

  • Anything that can move even small amounts of infested soil is capable of spreading SCN, including farm machinery, vehicles and tools, wind, water, animals, and farm workers.

How to choose SCN-resistant soybean varieties

Look for varieties that yield consistently well in SCN-infested fields on multiple sites (yield data from noninfested fields are not useful).

Look for varieties that consistently decrease SCN population densities or keep the SCN numbers in check in multiple fields. It is very difficult to reduce SCN numbers in a field once they develop to high levels, so it is important to consider how well SCN-resistant varieties control SCN numbers in order to maintain the productivity of fields for years to come.

Look for data from as many different reliable sources as possible, including university variety trials and strip trials conducted by co-ops, grain elevators, and seed companies.

Remember that high-yielding varieties don’t always control SCN population densities the best, so pay attention to information about SCN reproduction in the field as well as yield. Wise selection of varieties will ensure that soybeans can be grown profitably in SCN-infested fields for many years to come.

  • Agronomic impact

    Severe stunting and yellowing due to SCN infection is visible in this field. However, significant yield loss can occur from SCN feeding without causing above-ground symptoms - Photo: Greg Tylka, Iowa State University

    Up 30% yield loss can occur because plants are producing fewer pods than they should. The effect of SCN on soybean yield is directly related to the numbers of nematodes feeding on the root system.

    Above-ground symptoms
    The above-ground symptoms of SCN range from nonexistent to severe depending on the age and vigor of the soybean plants, SCN numbers, soil fertility, moisture levels, and other environmental conditions.

    Injury usually is more severe in light, sandy soils, but it also occurs in heavier soils. SCN damage is not always confined to smaller areas within a field. When fields are infested with SCN throughout, areas of stunted plants are not obvious.

    Below-ground symptoms
    Root symptoms of SCN often go unrecognized. Often it is difficult to recognize if roots are stunted and have fewer nodules unless they are compared to uninfected soybean plants. Symptoms of SCN infection include:

    • Dwarfed or stunted roots
    • Fewer nitrogen-fixing nodules
    • Increased susceptibility to other soil-borne plant pathogens
  • Life cycle

    The life cycle of SCN has three major stages: egg, juvenile, and adult female. The life cycle can be completed in 4 weeks under ideal conditions (soil temperatures at 75° F).

    From: SCN Life Cycle, Iowa State University

    SCN eggs released from a cyst - Photo: Terry Niblack

    Eggs develop into juveniles (J1, J2). The second stage juveniles enter the soybean root to feed and grow. Photo: Purdue University

    Females then lay 50-100 eggs in an egg mass on their posterior end. Finally, the female fills up with 200 or more eggs. Eventually, the egg-filled female dies and her body wall hardens to form a tough cyst around the eggs, as shown here. Photo: Terry Niblack

  • Scouting

    Field with confirmed SCN - Photo: Jason Bpnd, Southern Illinois University

    First, determine your purpose for scouting for SCN
    This will help determine your best strategy— whether to check soybean roots or to collect a soil sample — and when and how to collect the sample.

    Are you scouting to...

    • check if SCN is present in a field before planting next year's soybean crop? Collect a soil sample»
    • determine if your SCN management program has been successful in keeping SCN population densities in check? Collect a soil sample»
    • determine if SCN was responsible for poor soybean yields?
      Collect a soil sample»
    • look for SCN in stunted or yellow soybeans observed in mid-season, OR
      in fields that are apparantly healthy, but have not yet been checked for SCN? Examine soybean roots»

    What about HG tests?
    Much has been learned in the past several decades about development of SCN on resistant soybean varieties. It is apparent from this new knowledge that a change in how we describe the abilities of a SCN population to reproduce on resistant soybean varieties is warranted.

    A new system, called the HG Type test (HG for Heterodera glycines, the scientific name for soybean cyst nematode) has been developed and adopted by agronomists, plant pathologists, and soybean breeders. Read more about the new SCN HG Type test».

  • Distribution

    Heterodera glycines was first discovered in the United States in New Hanover County, North Carolina in 1954 and is believed to have been introduced from Asia. In 1987, the nematode was discovered in Ontario, Canada.

    Known distribution of the soybean cyst nematode, Heterodera glycines, in counties in the United States and Canada in selected years from 1957 to 2014. Known infested counties are indicated in red. Maps © 2014, C.C. Marett and G.L. Tylka, Iowa State University.
    Click to view enlargement

    At various times since these initial discoveries, maps were created of the counties in the United States and Canada that were known to be infested with the nematode. Recently, nematologists, plant pathologists, and state plant regulatory officials in the soybean-producing areas of the United States and Canada were surveyed to update the map of the known distribution of H. glycines in 2014.

    H. glycines has now been found in every soybean-producing state in the United States except New York and West Virginia. Since the last update of the map in 2008, H. glycines was discovered for the first time in 57 counties in 13 states, namely Kansas, Kentucky, Maryland, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Virginia, and Wisconsin.

    Reference: Tylka, G. L., and Marett, C. C. 2014. Distribution of the soybean cyst nematode, Heterodera glycines, in the United States and Canada: 1954 to 2014. Plant Management Network. doi:10.1094/PHP-BR-14-0006.

  • Management

    Sample fields to determine SCN population densities preferably before buying soybeans for the next season, but certainly before planting soybeans. Crop rotation and planting SCN-resistant varieties are the two most important strategies for SCN management.

    Infestation category Soybean not next crop to be grown Soybean next crop to be grown Management recommendation
    No SCN eggs detected 0 0 No management strategies are necessary. However, not finding SCN in a soil sample does not prove that it is not present in the field. Follow-up sampling is recommended to check for SCN infestations in future years.
    Low 1 - 4,000 1 - 2,000 If this is first discovery of SCN, follow the rotation described below starting with Year 1 the next time soybeans are to be grown. If Years 1 – 4 of the rotation described below already have been completed, continue with Year 5 of the rotation.
    Moderate 4,001 - 16,000 2,001 - 12,000 Begin Year 1 of the rotation described below the next time soybeans are to be grown.
    High >16,000 >12,000 Grow several years of a nonhost crop and sample field again every fall to monitor decrease in SCN population densities.
    NOTE: Egg counts are reported as eggs per 100 cm3 (about ½ cup) of soil and are only estimations of actual SCN population densities.

    Recommended crop rotations to manage SCN in fields with less than 5000 eggs/100 cc soil.
    Greg Tylka, Iowa State University.

    Crop Rotation
    Non-host crops, such as corn, sorghum, sunflower, oats, and alfalfa can reduce SCN population densities each year a non-host crop is planted.

    Dry beans are not a sutiable rotation crop, as SCN has been shown to develop and reproduce normally on 24 cultivars of dry bean plants.

    Suggested crop rotation to decrease populations of SCN
    Year 1 - SCN-resistant soybean with PI88788 source of resistance

    Year 2 - nonhost crop (such as corn, oats, alfalfa).

    Year 3 - SCN-resistant variety different than the one planted in Year 1.

    Note: If an SCN-resistant soybean variety with resistance from a source other than PI 88788 is not available for use in Year 3, grow a soybean variety with SCN resistance derived from PI 88788 that is different from the one that was grown in Year 1. Grow the exact same PI 88788 SCN-resistant soybean variety in Years 1 and 3 only if no other SCN-resistant soybean varieties with PI 88788 or other sources of resistance are available.

    Year 4 - nonhost crop (such as corn, oats, alfalfa).

    Year 5 - SCN-resistant variety different than the ones planted in Year 1 and Year 3, or susceptible soybean.

    Note: What determines whether a resistant or a susceptible soybean variety should be grown in this year? Almost all SCN-resistant soybean varieties available to north-central growers have the PI 88788 SCN resistance (“PI” stands for plant introduction). Because SCN-resistant varieties allow low level of reproduction, SCN populations can become “resistant to the resistance” as resistant varieties are repeatedly grown, especially if only one source of resistance is used.

    Growers concerned about this possibility can prolong the effectiveness of a single source of SCN resistance by growing a susceptible (non-resistant) variety when SCN numbers are low. But SCN causes much greater damage and seems to reproduce at a greater rate in hot, dry growing seasons than in years with adequate to excess rainfall. So if a severe drought is anticipated, growers might opt not to grow a SCN-susceptible variety in an SCN-infested field, even if SCN population densities are low.

    Year 6 - non-host crop (such as corn, oats, alfalfa).

    The popular SCN Management Guide is based on decades of research on soybean management in SCN-infested fields. It's now in it's 5th edition.
    Read online (pdf)»
    Order a print copy»

    Cultural practices
    Providing a plant the best possible growing conditions will reduce stress and yield losses due to SCN. Maintain optimum soil fertility to optimize plant growth and development.

    Weed control not only reduces plant stress, but some weeds act as alternate hosts of SCN. Disease and insect control maintains plant health and minimizes damage due to SCN.

    Weed control
    On their own, winter annual weeds and soybean cyst nematode (SCN) can cause significant problems in soybean fields. But now, researchers in Indiana have identified six winter annual weeds that act as alternate hosts to SCN:

    • Purple deadnettle (strong host)
    • Henbit (strong host)
    • Field pennycress (moderate host)
    • Shepherd’s-purse (weak host)
    • Small-flowered bittercress (weak host)
    • Common chickweed (weak host)

    The Purdue researchers documented SCN reproduction on purple deadnettle and henbit in the field, and noted that reproduction in the greenhouse was as efficient as reproduction on SCN-susceptible soybean.

    This means that fields with these weed hosts may be increasing SCN population densities at a faster rate than fields without these weeds. A recent study in Indiana found that known SCN weed hosts were prevalent in 93 percent of the fields surveyed (Creech and Johnson, 2006), indicating the possibility of a statewide increase in nematode population densities due to weeds.

    Read more in the recent full-color extension publication from Purdue University Winter Annual Weeds and Soybean Cyst Nematode Management»

    Sanitation
    Avoid spreading SCN from infested to noninfested fields. If possible, plant noninfested fields first and power wash equipment after working infested fields.

    Nematicides
    Nematicides will reduce yield loss of SCN-susceptible varieties planted in infested fields but increases the cost of production. Although nematicide will give early season protection against yield loss they do not reduce nematode population densities. Final SCN population densities are often as high as if a nematicide had not been used.

    In general, nematicide use should be considered only where adapted resistant varieties are unavailable and where susceptible varieties are planted and SCN population densities are above the threshold level.

    Preplant soil sampling
    Sampling can be done following either soybeans or corn. If samples are taken in a soybean field, sample only the margins of affected areas, not the centers.

    Sample fields to determine SCN population densities preferably before buying soybeans for the next season, but certainly before planting soybeans.

    Check roots during midseason for the presence of females and cysts. Although SCN population density is only one component in soybean yield loss, it may suggest potential yield loss and is information vital for sound SCN management decisions.

    The various details to consider when interpreting results of soil tests for SCN are explained in Interpreting SCN Soil Testing Results. (pdf, Iowa State University).

    Reference
    Creech, J. E., and W. G. Johnson. 2006. Survey of broadleaf winter weeds in Indiana production fields infested with soybean cyst nematode (Heterodera glycines). Weed Technol. 20:1066-1075.

  • HG types

    An HG type describes the ability of the SCN population to reproduce on resistant soybean varieties. Shown is a brown cyst (egg sac) on a soybean root.

    An HG test in progress.
    Step 1. Soybean lines with different resistant genes are inoculated with nematodes and allowed to grow for 30 days.

    Step 2.The soybean roots are washed over a sieve to collect the females.

    Step 3. The number of females that have developed on each soybean line are counted, and compared with the number on a standard variety - Photo: Terry Niblack, Ohio State Unviversity


    What are HG Types?
    The soybean cyst nematode (SCN) is a widespread and serious pest of soybeans. The microscopic worm is long-lived in the soil, can develop and reproduce quickly on susceptible soybean varieties, and is capable of causing significant yield loss even in years with ideal growing conditions.

    Fortunately, soybean varieties have been developed that are resistant to SCN. These resistant varieties suppress 90% or more of the development of most SCN populations, resulting in a significant increase in soybean yields in SCN-infested fields.

    However, soon after the release of resistant varieties, scientists discovered some SCN populations that were capable of reproducing at elevated levels on resistant soybean varieties. Consequently, a race test system was developed in 1970 to assess the abilities of SCN populations to reproduce on resistant soybean varieties.

    Much has been learned in the past several decades about development of SCN on resistant soybean varieties. It is apparent from this new knowledge that a change in how we describe the abilities of a SCN population to reproduce on resistant soybean varieties is warranted.

    A new system, called the HG Type test (HG for Heterodera glycines, the scientific name for soybean cyst nematode) has been developed and adopted by agronomists, plant pathologists, and soybean breeders.

    What is a SCN HG Type test?
    A HG Type test is a greenhouse test performed on a SCN population isolated from a field to determine how well the SCN population can develop on soybean lines that were used as sources of resistance for SCN-resistant soybean varieties.

    Why not a SCN race test?
    The HG Type test is similar to a SCN race test, but includes only soybean lines that are sources of resistance in available SCN-resistant soybean varieties. It is much easier to understand than the race test. Once the HG Type test system has been used for a while, it should be easy to remember what an HG Type designation means in relation to the resistance possessed by available SCN-resistant soybean varieties.

    For example, if the HG Type of a SCN population in your field has the number 2 in its designation, you will come to recognize that the number 2 corresponds to PI 88788, the most commonly available source of resistance in soybean varieties in the Midwest. The number 2 means the same thing whether the population is an HG Type 2, an HG Type 2.3.7, or an HG Type 1.2.6.

    Who needs an HG Type test?
    Soybean growers who have experienced sub-par performance from SCN-resistant soybean varieties in SCN-infested fields should consider having an HG Type test performed. Also, soybean growers who farm in an SCN-infested area that has had resistant soybeans grown numerous times in the past might consider having an HG Type test performed.

    How is a HG Type test conducted?
    To determine the HG Type of a SCN population, we put the nematodes on soybean lines with different genes for SCN resistance in the greenhouse under controlled conditions (Figure 1). These conditions are similar to those under which resistant soybean varieties are developed.

    After 30 days, enough time for SCN females to develop, we count the numbers of females that form on the roots of the various resistant soybean lines (Figures 2 and 3). We compare these numbers to the number of females that formed on a standard susceptible soybean variety. Finally, we note which resistant soybean lines show elevated development by the SCN population. “Elevated development” means that a resistant line has 10% or more of the number of females that developed on the susceptible variety.

    How do I interpret the results of a HG Type test?
    The number or numbers in the HG Type designation correspond directly to sources of resistance used in available SCN-resistant soybean cultivars.

    For example, a SCN population of HG Type 1.2 indicates that the nematode population has elevated development on Peking (line #1) and PI88788 (line #2). Either or both lines have been used to breed some SCN-resistant soybean varieties. A grower with a field infested with an HG Type 1.2 might not want to plant SCN-resistant varieties that contain resistance from Peking or PI88788, if possible. Facilities that provide SCN HG Type testing should also offer assistance in interpreting the results of the test.
    Examples of HG Type Testing»

    How do I interpret descriptions of public and private SCN-resistant varieties?
    Growers should be aware that the traditional way that SCN-resistant varieties are labeled is somewhat misleading. For example, an SCN-resistant variety with resistance from PI 88788 may be labeled as resistant to SCN race 3, when in fact it might also be resistant to as many as seven additional SCN races. In addition, this variety also might be vulnerable to elevated development by as many as eight other SCN races. Unfortunately, none of this management-type information is conveyed in the labeling.

    With the HG Type designation, we label the nematodes, not the varieties. For example, if a grower’s SCN population is an HG Type 2, the name clearly indicates that the nematode exhibited elevated development on PI 88788 (line #2). That makes it more likely that the nematodes could develop on any SCN-resistant variety that obtained its SCN resistance from PI 88788, and it likely would be in the grower’s best interest to use a SCN-resistant variety that obtained its SCN resistance genes from a source other than PI 88788, if possible.

    Examples of HG Type Testing»
    Where can I get a SCN HG Type test performed?»

  • Resources

  • Photo Gallery

    Distribution of SCN in the United States as of November 2008.

    Signs of SCN on soybean roots - Photo: Craig Grau, University of Wisconsin

    SCN cysts, and nodules, on soybean roots - Photo: Craig Grau, University of Wisconsin

    Poor root system of SCN-infected plant. Nodules are also seen - Photo: Craig Grau, University of Wisconsin

    Signs of SCN on soybean roots - Photo: Craig Grau, University of Wisconsin