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S.
Sardanelli and F. Ellison
Nematology Series, NDRF Fact Sheet No.2 Revised September 2005 |
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Plant-parasitic nematodes are nearly microscopic, worm-shaped animals virtually invisible to the naked eye when in the soil. They can cause significant plant damage ranging from negligible injury to total destruction of plant material. The severity of plant injury resulting from nematode activity depends on several factors such as the combination of plant and nematode species and prevailing environmental factors including rainfall, soil types, land contour, and culture practices.
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| Scanning electron micrograph of a second-stage root-knot nematode juvenile propped up against a human hair (Eisenback) | Meloidogyne incognita penetrating cucumber roots as seen with scanning electron microscopy(McClure) |
Many plant-parasitic nematodes have a wide host range while a few are host
specific.
· Nematodes also feed and reproduce on many different weeds.
· The survival of some nematodes for at least one-year in moist soil
without a host plant is common.
· Many kinds of plant-feeding nematodes can survive freely in the soil
through winter- even if the soil is frozen.
· A few plant-parasitic nematode species can survive in the soil in
a dormant state within cysts for many years.
· Oval areas or irregular patches in the field with poor plant growth ranging from a few feet to hundreds of feet across.
· Poor, sickly growth, wilting, yellowing, stunting, and premature plant aging.
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| Discoloration of American boxwood associated with Pratylenchus vulnus.(Barker) | Field symptoms (patchy stunting and chlorosis) of soybean cyst nematode, heterodera glycines, on soybean.(Barker) |
Hundreds of different species of
nematodes are associated with plants
· Not all nematodes are plant parasites.
· In many cases those that are plant parasitic occur in populations
too small to cause serious plant injury.
· Extracting and identifying the nematodes from soil samples or infected
plant parts are the only positive means for determining if and which nematode
species are responsible for poor growth.
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| Baermann funnels for extraction of motile nematodes. (Zunke) |
Nematode Management
· The individual situation determines the use of management tactics.
· The degree of plant damage varies with the kinds and numbers of nematodes
present, the kind and variety of plant, and the cultural and environmental
factors involved.
· Management tactics rarely destroy all plant-parasitic nematodes,
but rather reduce the population(s) to levels below which economic damage
occurs.
· When control measures are recommended, it is often necessary to repeat
the measures periodically to maintain satisfactory plant growth.
The following widely recognized Integrated Pest management (IPM) strategies
are critical to management of plant-parasitic nematodes.
Prevention: This strategy
should be the first line of defense. Prevention is the practice of keeping
a population of nematodes from infesting a site and specific tactics include:
· Education regarding nematode presence, biology, and management.
· Survey sampling of an intended planting site to determine the degree
of existing nematode activity.
· Use of nematode free transplants.
· Careful Examination of transplant roots before planting. Plants already
infected when put into the ground will not grow well and can introduce nematodes
to the site that attack present and future susceptible plantings.
· Weed control as a means of eliminating nematode access to alternate
hosts.
· Sanitation practices such as cleaning of equipment between sites
of operation.
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| Cleaning a tractor with compressed air to remove soil containing the soybean cyst nematode, Heterodera glycines. |
Avoidance: practiced when
nematode populations exist in a site, but their impact can be avoided or lessened
through some cultural practice. Examples of avoidance tactics include:
· Sampling to determine nematode species and population levels.
· Choosing plant materials that are poor hosts.
· Practice crop rotations that include nonhost, resistant and susceptible
crops when feasible.
· Employ cultural practices known to be optimal for plant maintenance.
Monitoring: includes tracking
and proper identification of nematodes and includes:
· Routine sampling to maintain records of incidence and distribution. These samples form the basis for crop rotations, cultivar selection, economic thresholds, suppressive actions, and other management decisions.
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| Development of soybean cyst nematode, Heterodera glycines, on resistant (left) and susceptible (right) soybean varieties. (C. J. Southards) |
Suppression: nematode suppressive tactics may become necessary to avoid economic crop loss where prevention and avoidance tactics are not successful. Suppressive tactics include:
· Addition of organic matter and green manure crops to encourage the release of microorganisms detrimental to nematode development or survival.
Nematode Suppressive Crops - Auburn University -
http://www.aces.edu/pubs/docs/A/ANR-0856/
Chemical Management
· Chemical control involves the application of certain volatile (fumigants)
and nonvolatile nematicides to the soil to reduce nematode populations. It
is important here to note:
· There are some nematode problems for which there currently is no
legal, effective nematicide.
· Chemical management reduces nematode populations for a limited period
of time. Nematodes that escape treatment can resume feeding when the chemical
is gone.
· Nematicides are severely restricted for landscape application.
· Because they are highly toxic, several nematicides that are registered
for ornamental plants are restricted to commercial production.
· There is presently no effective nematicide that may be applied legally
to ornamentals already planted in the landscape.
Recommendations for the application of nematicides may be found in the University of Maryland's current Extension publications.
All pictures are courtesy of Nemapix Jounal of Nematological Images, vol.
1 &2, J.D. Eisenback & Ulrich Zunke, eds.
The University of Maryland is equal opportunity. The University's policies, programs, and activities are in conformance with pertinent Federal and State laws and regulations on nondiscrimination regarding race, color, religion, age, national origin, gender, and disability. Inquiries regarding compliance with Title IV of the Civil Rights Act of 1964, as amended: Title IX of the Educational Amendments: Section 504 of the Rehabilitation Act of 1973: and the Americans with Disability Act of 1990: or related legal requirements should be directed to the Director of Personnel/Human Relations, Office of the Dean, College of Agriculture, Symons Hall, College Park, MD 20742.
For comments and questions regarding this internet site contact ssardane@umd.edu.
