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Soybean Cyst Nematode

S. Sardanelli
Reviewed April 2010

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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Life Cycle

Heterodera glycines lifecycle Heterodera glycines
Drawing of the life cycle of soybean cyst nematode, Heterodera glycines (McGawley) Painting of the soybean cyst nematode, Heterodera glycines. (Cush)
Second-stage juveniles of soybean cyst nematode penetration the root Infective second-stage juveniles of soybean cyst nematode penetrating roots
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)

Six stages are involved in the life cycle of this nematode: an egg stage, four juvenile (larval) stages, and the adult stage.

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.

Heterodera glycines, broken open to reveal eggs Eggs containing second-stage juveniles Females compared to a nodule
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)

As in other species of Heterodera, physiological races or biotypes have been identified for the soybean cyst nematode. These races differ in ability to develop on different soybean varieties. Therefore, in any program of control or breeding for resistance, the question of race must be considered.

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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:

Above Ground Symptoms-

Field infested closeup of infected soybean
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
Heterodera glycines
Soybean cyst nematode, Heterodera glycines, on soybean (McGawley)

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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.

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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:

Sanitation measures

cleaning a tractor
Cleaning a tractor with compressed air to remove soil containing the soybean cyst nematode, Heterodera glycines.
  • Farm machinery and clothing, especially footwear, should be cleaned before moving from a known infested area to an uninfested site.
  • 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.

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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 Varieties

  • Soybean varieties with resistance to soybean cyst nematode have been developed and are available to growers.
  • 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.
infested field
Resistant and susceptible soybeans growing in a Heterodera glycines infested field (J. P. Ross)
  • Over-use of resistant varieties can lead to the emergence of new strains or races of nematodes.
  • Susceptible varieties should occasionally be used in rotational plans rather than growing resistant varieties continuously.
  • 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.

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Chemical Management

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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