Professor of Plant Pathology and Extension Plant
Pathologist, Dept. Plant Pathology, NDSU
Visit the NCSRP Plant Health web sitefor more information
Funding for the development of this information
was provided by the North Dakota Soybean Council
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The soybean cyst nematode (SCN), Heterodera glycines is
the most important soybean pathogen in the United States. In 2002,
the estimated losses from SCN in the USA were 133 million bushels.
The nematode attacks the roots causing major damage to the plant.
This nematode was first reported in Japan in 1915, and was found
in North Carolina in 1954. It probably was imported along with soybean
seed from Asia. The nematode has spread throughout the soybean growing
the Midwest, southeast, eastern seaboard and into Canada. It was
first reported in Minnesota in 1978 and in South Dakota in 1995.
It now occurs in western Minnesota counties and in the northern
counties of South Dakota bordering ND. In August, 2003, SCN was
found in eastern North Dakota, but the number of infested soybean
acres has not yet been determined.
Symptoms of SCN on soybeans consist of yellowing and stunting
of plants that usually occur in patches in a field.
Identification of this disease may be difficult because yield loss
can occur with no obvious above ground symptoms. Declining soybean
yields may be the indication of an SCN problem. When growing conditions
are optimal, infected plants may appear nearly normal. When above
ground symptoms appear, it usually indicates a long term problem
that is just being recognized. SCN populations can require many
years from initial infestation to reach damaging levels. Although
above ground symptoms of SCN damage are common, especially at high
populations of nematodes in the soil, they are highly varied and
can be confused with other causes such as iron deficiency, high
pH, soil compaction, nutrient deficiency, chemical injury, or root
rots. Yellowing of the foliage (chlorosis) in July or August, stunting
of plants, thin stands and slow closing of rows are observed. A
wavy growth pattern may be seen down the rows due to stunted and/or
poorly growing plants. Symptoms may first occur near field entrances,
vehicle and storage areas in the field, compacted headlands, along
fence rows where windblown soil accumulates, on the tops of knolls
or in low or flooded areas. Leaf yellowing may not be observed at
low to moderate levels of SCN, but often appear on infected plants
stressed by drought. SCN can cause various types of chlorosis that
can be confused with nutrient deficiency. Disease often occurs more
pronounced in certain parts of a field as circular or oval shaped
areas, and the pattern of symptoms will follow the direction of
tillage. Weeds may infest the affected areas. This patchy pattern
is very evident when viewed from the air. In highly infested fields,
plants can be severely stunted with few pods developed or the plants
The swollen female nematodes (arrow) on the
roots of soybean.
The most definitive characteristic of SCN is the presence of the
swollen female nematode on the roots. If the plant is dug from the
soil (not pulled up) and the soil carefully removed from the roots,
the whitish, cream colored to yellowish, lemon shaped nematodes
(about 1 mm diameter) on the root surface are visible. They are
smaller than nitrogen-fixing nodules. In light soils they are usually
easy to observe, while in heavy soils it is more difficult to remove
the soil without damaging the nematode. At high populations of nematodes
it is easier to find them on the roots than at low populations.
The swollen live females are usually observed from about mid June
to mid August. Later in the season the female nematodes turn into
dark brown cysts and it is harder to see them and they are easily
detached from the roots when removing the soil. The roots of SCN
infected plants are usually dark, necrotic and stunted and there
is poor nodulation.
Losses of 15 to 30 percent have been reported even when there are
no obvious above ground symptoms. In southern Minnesota, about 20
percent of the soybean acreage on selected farms in 1989 was estimated
to lose 10 bushels/acre or more due to SCN. When the nematode is
abundant, losses can exceed 20 bushels/acre. If nematode populations
are extremely high and the environment is conducive to disease development,
almost no crop will be produced.
SCN LIFE CYCLE AND DISEASE DEVELOPMENT
The soybean cyst nematode overwinters in the soil as eggs within
the female carcass. When eggs hatch, a second-stage larva emerges
and moves a short distance through the pores in the soil to the
root tips of soybean. The roots release chemicals that attract the
nematode. The nematode has a hollow stylet (mouthspear) that is
used to penetrate the root tip cells and allows the larva to enter
the vascular tissue. A specialized feeding site is established in
the root and the nematode becomes sedentary then enlarges and molts
three times before becoming an adult. The female adult enlarges
and her body breaks through the root tissues becoming visible on
the root surface, but she remains attached to the feeding site.
The first adult females may be visible by June and will be observed
throughout the summer, but their numbers decline in the late summer
and fall. The male adults become slender roundworms and thus are
not visible to the unaided eye.
The second stage larva of SCN next to an empty egg case
(left photo). This larva will infect the soybean root. Magnified
about 300 times. The right photo shows the stylet (arrow) in
the head of a larva.
The female produces hundreds of eggs and some are deposited outside
her body. Those eggs can hatch and start the life cycle again resulting
in new infections of roots. In southern Minnesota, about 3 generations
are expected in a favorable year. Many eggs, however, are retained
within the female body which upon death becomes a brown cyst. The
cyst is a durable structure that protects the eggs and promotes
survival in the soil.
SCN populations have historically been classified into different
"races" that were characterized by their ability to reproduce
on soybean varieties (known as differentials) with three different
sources of genetic resistance. Because the variability of SCN populations
were not fully described by the race system, a new system of characterizing
SCN populations has recently been devised known as the HG type test
(HG is for Heterodera glycines ). With the HG type test, SCN populations
are characterized by their ability to reproduce on soybean varieties
(known as indicator lines) with seven different sources of genetic
resistance. After a SCN population has been characterized using
the HG type test, a grower can determine which sources of resistance
to grow that would minimize the buildup of SCN in a particular field.
SCN populations present in Minnesota and South Dakota have not been
characterized using the HG type test at the current time; however,
they have been characterized using the old race system. Races 1,
3, 5, 6, and 14 are present in MN, with race 3 being the most common
throughout the state. Race 3 is also present in SD.
The nematode feeding in the roots disrupts the normal physiology
of the soybean plant, and results in disease. Roots become very
susceptible to other root rots, they have less nitrogen fixing nodules,
and are less capable of taking up water and nutrients. The severity
of SCN damage is dependent on the population of the nematode, the
soybean cultivar, weather conditions, soil conditions, and cultural
practices. Warm, drier soils, and sandy soils usually favor disease
development. Symptoms tend to be more pronounced when plants are
under stress from drought, low soil fertility, soil compaction or
other types of damage. Since many factors, especially growing conditions,
affect disease, the amount of damage each year can vary substantially.
SCN is easily spread from infested to non-infested fields through
contaminated field equipment, in wind blown or water carried soil,
by animals or by soil "peds" (small clumps of soil) in
seed harvested from infested fields.
Adult females (white) and brown cysts of SCN. Magnified
about 20 times. Click on photo to increase size.
MANAGEMENT OF SCN
Preventing the infestation of fields should be the first step in
managing this pathogen. Stopping or slowing the spread of SCN can
prevent losses in the following years.
Early identification of SCN is important to developing an SCN management
plan for profitable soybean production. Management of SCN has two
goals: Preventing the infestation of fields by SCN and reducing
the nematode populations in infested fields. In addition, the use
of cultural practices, such as adequate soil fertility, and reducing
plant stress from weeds, insects, etc, to promote good growth of
soybean will reduce the damaging effects of SCN. Research results
have been variable when comparing the effects of conventional versus
reduced or no-tillage operations on SCN survival or disease development;
therefore, there are no recommendations on tillage. No-till, however,
may slow the spread of SCN in a newly infested field.
If some acreage is infested with SCN, always work non-infested
fields before the infested fields to reduce the risk of carrying
SCN between fields. Equipment used in infested fields should be
thoroughly cleaned of soil before entering non-infested fields.
Avoid using seed harvested from an infested field because the nematode
could be in soil "peds". Also, avoid 'bin-run' seed. Use
tillage or other practices that reduce the wind or water transport
of soil and debris from infested to non-infested fields.
Determine SCN population ( more information-
Determining the population of the nematode in the soil is the first
step in managing SCN. This is accomplished by soil sampling and
sending the soil samples to a qualified laboratory that can determine
the number of nematode eggs in the sample. You cannot estimate the
population of SCN in a soybean field by looking at the presence
of the nematode on the roots. Soil sampling in the fall following
a soybean crop is a good time to take samples. Use a soil probe
or small trowel and collect 20 soil samples 6-8 inches deep (about
1 cup per sample) in a zig-zag pattern every 10 to 20 acres. Collect
samples from areas of similar soil type or crop history or possibly
only sample areas where you suspect SCN problems. Combine the samples
from every 10 to 20 acre set in a bucket and mix very thoroughly.
Place about 1 pint in a plastic bag, label the samples and store
in a cool, dark place until shipped to a lab. Include your name,
address, phone number, sampling date, acres sampled, crop history,
location of each field and indicate the sample numbers and labels.
A list of laboratories that determine SCN populations is included
in this bulletin. At low nematode populations (below 200 eggs/100
cm3 of soil) it is difficult to detect eggs in the soil. A soil
sample that is negative for SCN, therefore, does not guarantee there
is no SCN. If SCN is reported in your immediate area, keep monitoring
your fields for SCN. Maintain records of egg populations to determine
the best rotations for your farming operations.
Reducing SCN populations (more information-
Crop rotation to non-hosts and the use of host resistance are the
principal methods of reducing nematode populations. Examples of
non-host crops are small grains, corn, sunflower, sugar beet, flax,
potato, alfalfa, forage grasses, sorghum and canola. Field pea is
considered a poor host, thus may be used in a rotation. Dry beans
are hosts of SCN, and should not be in a rotation (see list of hosts).
Effective weed control is also necessary because there are some
weed hosts. Research from adjacent states suggests that a three
to four year rotation to non-host crops will reduce moderate levels
of nematode populations below the economic threshold. Heavily infested
fields might require 4 or more years in rotation to non-hosts. Before
a decision is made to plant susceptible soybeans again, sample the
soil and have it analyzed for the egg population.
SCN resistant soybean cultivars can also be used in the rotation.
Resistant soybeans allow growers to produce a soybean crop and either
reduce or not allow the SCN population to increase. In Minnesota,
resistant soybeans have performed well in soils with egg counts
up to 2,000 eggs/100 cm3 of soil. At higher populations, resistant
soybeans might be damaged by SCN. Resistant cultivars, however,
may not be the best yielding cultivars, therefore, only use them
when SCN populations are too high for growing susceptible cultivars.
With low infestations of SCN your high yielding susceptible cultivar
may still yield more than a resistant cultivar. However, at the
end of the season the egg counts may be to high to grow another
susceptible cultivar the following year. This is where soil sampling
to determine egg counts is needed to make cultivar decisions.
An example of a rotation for an infested field might be: year 0
- identification of SCN; yr 1 - non-host crop; yr 2 - non-host crop;
yr 3 - resistant soybean; yr 4 - non-host crop; yr 5 - susceptible
soybean (if egg population is below threshold - see following paragraph).
Rotations using non-hosts and resistant soybeans can be tailored
to the infestation levels of each field. There are few SCN resistant
soybeans adapted to North Dakota, but such cultivars are under development
by both public and private breeders. Some cultivars reported to
be resistant to SCN which could be used in ND are listed below.
To prevent shifts in SCN races within a field, alternate sources
of resistance when continually using resistant soybeans in a rotation.
SCN resistant soybean varieties available for the 2004
growing season in North Dakota
Source of resistance
Stine Seed Company
Univ. of Minnesota
Stine Seed Company
United Agri Products
NuTech Seed Co.
PFS 0411 NR
Peterson Farm Seeds
Stine Seed Company
Sabre Initiatives, LLC
NuTech Seed Co.
Sabre Initiatives, LLC
Prairie Brand Seed Company
Wensman Seed Company
SOI Brand 1343NRR
Sand Seed Service, Inc.
Pioneer 91B42 SCN
Pioneer Hi-Bred International
This list may not be complete. Mention of a tradename or product
does not constitute recommendation by North Dakota State University
or the NDSU Extension Service.
A susceptible (left) and resistant (right) soybean cultivar
on soil infested with SCN. These cultivars are the same age.
Notice the less vigorous growth and open rows in the susceptible
cultivar compared to the resistant one. There are no obvious
above ground symptoms of infection by SCN in the susceptible
cultivar, but growth is reduced.
Thresholds (more information- )
Research from adjacent states suggests that 100 to 150 eggs per
100 cm3 of soil can cause some yield loss in susceptible soybeans.
Yield loss increases as egg counts increase. Start a rotation to
non-hosts or grow resistant soybean when the egg counts are near
this level. Remember that growing a susceptible soybean in a field
with low eggs counts may not cause high yield losses, but the high
reproduction of the nematode on that cultivar can result in greater
than a 5 to 10 fold increase in the egg population by the end of
the season. That results in a greater SCN population that must be
managed for the following years. Fields with high egg counts (>
2,000 eggs/100 cm3 of soil) should be rotated first to non-hosts
to reduce SCN levels before planting a resistant soybean. Although
resistant soybeans can be grown in fields with high egg counts (2,000-5,000
eggs/100 cm3 soil), SCN may cause some yield loss. Growers need
to balance the need for high yields against the need to manage the
Nematicides are not commonly recommended to control SCN in the
northern soybean growing areas. In general, they are not as effective
or as economical as other control methods. Nematicides can provide
early season protection, but not season-long control. Many factors
such as soil type, and weather affect the results obtained from
nematicides. Always determine if chemicals are registered for use
in your state before attempting to use on a crop.
HOST PLANTS FOR SCN (only a partial
listing of hosts)
Beans (green, snap, bush, lima, dry,)
Clovers, scarlet, crimson
Cowpea or black eyed pea
Lupines, white & yellow
Sweet clover, crimson clover
Vetch, common, winter
Chickweed, common & mouse-ear
Milk & wood vetch
Rocky Mountain Beeplant
LABORATORIES THAT ANALYZE SOIL FOR SCN
These laboratories are close to North Dakota; there are others in
the Midwest. Call and request information on cost, time for sample
analysis, and any information or payment that may be required before
processing the samples. Ask specifically if egg counts are performed.
Some laboratories may count cysts or eggs. Request egg counts. Generally
laboratories will express the results as number of eggs per 100
cc (cubic centimeters) of soil. Some labs will express the results
as eggs and juvenile larva per volume of soil.
902 13th St. N
Benson, MN 56215
Tel: 320- 843-4109
51 West Lincoln Way
Nevada, IA 50201
Tel: 515- 382-3084
Fax: 515- 382-5644
North Dakota State University
P. O. Box 5012
Fargo, ND 58105-5012
University of Minnesota
Southern Experiment Station
35838 120th St.
Waseca, MN 56093-4521
Plant Disease Clinic
323 Bessey Hall
Department of Plant Pathology
Iowa State University
Ames, Iowa 50011
Acknowledgment: The authors thanks Drs. Senyu Chen, Len Francl
and A. Lamey for helpful comments.
This bulletin was originally published in 1999 and revised in
Photo credits: Field symptoms and resistant and susceptible
soybeans courtesy of J. D. Smolik; nematodes on roots courtesy of
G. Tylka; white females and cysts together courtesy of T. Niblack;
other photos by the B. Nelson.