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S.
Sardanelli and F. Ellison
Nematology Series, NDRF Fact Sheet No.3 Revised September 2005 |
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Introduction
Due to its severe injury to host plant roots, rapid reproduction and persistence
in the soil, the soybean cyst nematode is considered a serious agricultural
pest. The life cycle of the soybean cyst nematode is completed in about one
month. It is possible to have three to six generations in a single cropping
year, depending upon location. Soybean cyst nematodes enter the root tissue
of susceptible plants and feed internally.
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| Drawing of the life cycle of soybean cyst nematode, Heterodera glycines (McGawley) | Painting of the soybean cyst nematode, Heterodera glycines. (Cush) |
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| Second-stage juveniles of soybean cyst nematode penetration the root of soybean (stained red) (Eisenback) | Infective second-stage juveniles of soybean cyst nematode penetrating roots (stained red) (Eisenback) |
The second stage juvenile is the mobile and infective stage, worm-like in appearance and unable to be seen with the naked eye. It penetrates the roots and punctures the cells with a spear-like structure (stylet), then migrates toward food-conducting tissues where it feeds.
Nematode feeding activities, alters the anatomy of the root system. As a result, normal root function is disrupted and translocation of water and nutrients is impaired.
The female can produce 50 to several hundred eggs, the majority of which remain inside the female body. Others are deposited in a gelatinous mass in the soil. After the female dies, the body remains intact and hardens into a tough leathery sac known as a cyst. Eggs and juveniles can persist in these cyst bodies for several years until they are stimulated to hatch in the presence of host plants.
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| Soybean cyst, Heterodera glycines, broken open to reveal numerous eggs contained inside (McGawley) | Eggs of soybean cyst nematodes containing second-stage juveniles (McGawley) | Female soybean cyst nematodes, Heterodera glycines, compared to a nodule on the root system (McGawley) |
Recognizing the Presence of Soybean Cyst Nematode- when poor plant growth is observed in a soybean field, the possibility of soybean cyst nematode infestation should be considered:
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| Soybean field infested with soybean cyst nematode, Heterodera glycines (Eisenback) | Closeup of soybean stunted from infection by soybean cyst nematode, Heterodera glycines (top) (Eisenback) |
· Circular patches of plants which exhibit much poorer growth than the surrounding areas
· Stunting, yellowing, wilting
· Significant reduction in yield
Below Ground Symptoms- dig roots
and carefully remove excess soil. Any or all of the following may be observed:
· A shallow bushy root system
· Drastically reduced root system and root necrosis in heavily infected
plants
· Inhibition of rhizobium nodule formation on the roots
· A hand lens is usually required to detect the presence of cyst bodies
on the roots
· Cysts are approximately 1/4 to 1/2 the size of a pinhead
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| Soybean cyst nematode, Heterodera glycines, on soybean (McGawley) |
Sampling and Diagnosis
Should the presence of soybean cyst nematode be suspected, samples should
be taken. The Nematode Diagnostic Laboratory "Sampling Procedures" fact sheet outlines
the methods for accurate sampling. For scouting information, refer to
"Scouting
for Soybean Cyst Nematode"(an acrobat file requiring Adobe
Acrobat Reader), by the Iowa State University Extension service.
Management of Soybean Cyst Nematode
The existence of the cyst, containing viable eggs and juveniles, is the single
most important factor which makes the soybean cyst nematode so difficult to
control. The tough cyst body, besides providing long-term protection for eggs
and juveniles, also provides the possibility of long distance dispersal. Cysts
are found in "soil-peds" (aggregates of soil) which adhere to anything
that moves through the infested field. Therefore, in order to restrict the
spread of soybean cyst nematodes to uninfested areas, and to control the populations
in known infested fields, the following management practices are necessary:
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| Cleaning a tractor with compressed air to remove soil containing the soybean cyst nematode, Heterodera glycines. |
· The movement of contaminated materials, such as nursery plants, root crops, and poorly cleaned seed, containers used in transport, from an infested area, is a primary means of spread for soybean cyst nematode.
· Because this nematode has a number of weed species as hosts, weed control is an aid in control of nematode population buildup.
Crop rotation
· A nonhost crop should be planted for two (preferably three) years
between the planting of susceptible soybean crops
· The fact that rotation might not be economically acceptable to the
grower must be considered
· Any plan for the use of crop rotation as a control method must be
designed with the knowledge of the existing nematode population(s) in the
field and the specific crop to be grown.
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| Resistant and susceptible soybeans growing in a Heterodera glycines infested field (J. P. Ross) |
· These resistant varieties are not severely damaged by the nematode and can reduce the population by literally starving the nematode.
· Resistant varieties will not eradicate the cysts but their use will eliminate the necessity of lengthy rotations and allow the grower to produce crops for which his agricultural operations were designed.
· Over-use of resistant varieties can lead to the emergence of new strains or races of nematodes.
· An alternative would be to use a resistant variety for one or two seasons only and rotate with a nonhost crop when feasible.
· Extensive breeding programs are developing new varieties in the state.
· In Maryland the races most commonly detected have been races 1 and 3.
For additional information concerning Maryland Soybean Variety Tests, see "Agronomy Facts No. 32" provided by the Maryland Cooperative Extension Service as a PDF or Word document.
Chemical Management: Involves
the use of certain non-volatile nematicides, which are applied to the soil
to reduce nematode populations.
Recommendations may be found in current University of Maryland Extension
Service publications.
Nematode populations cannot be eradicated, but can only be reduced to economically insignificant levels. The reduction of nematode numbers is accomplished through use of the above-mentioned management tactics. The fact that cyst contents may remain viable in fallow soil for years ranks this nematode among those with the greatest longevity in the soil. However, with proper management and utilization of specific control measures, successful soybean production can continue in infested fields.
All pictures are courtesy of Nemapix Jounal of Nematological Images, vol. 1 &2, J.D. Eisenback & Ulrich Zunke, eds.
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