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Soil Sampling to Assess Cotton Nematode Population Distributions and Densities

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Purpose of Soil Sampling: To accurately determine nematode species, population distributions and densities in a specific area.

Factors Influencing Distribution and Density: Time of year, previous crop, soil texture, and nematode management practices used. If nematodes are present, distribution is generally patchy in a field.

Best Time to Collect Soil Samples: Guidelines vary between states. Generally, summer or late fall is recommended. Populations are usually low in spring and build through the growing season to reach peak densities at harvest. Samples should be taken before cultivation when rows are still in place. Populations concentrate around existing root zones.

Number of Samples to be Collected: The number of samples to be taken is usually based on the value of the information to be gained compared to the cost of collecting the samples, plus laboratory fees for extracting the nematodes.

  • Costs are based on the number of samples collected, analyzed, and evaluated.
  • The greater the number of samples collected, the more accurate and reliable the estimate will be.
  • The cost of an accurate population assessment should not exceed the cost of nematode management and the benefits of control.
  • Balancing the number of samples (and related costs) with the value of correct decisions requires experience and knowledge coupled with the understanding of nematode sampling.

Plans Prior to Collecting Soil Samples: It is important to look for clues that may be present in the field prior to sampling.

  • Review previous cropping patterns.
  • Assess soil texture and changes in the field.
  • Identify weak spots in the field and look for plant symptoms.
  • Divide the field into areas based on crop history and soil type to increase cost effectiveness of sampling. Sampling is more valuable in a divided field, because the final estimate is more accurate and reliable.
  • After the field is divided into areas based on crop history and soil type, then subdivide these areas into blocks of about 10 acres. Treat each area where growth has been poor as a separate block, even if it is smaller than other blocks.

Collecting Soil Samples: Each sample should represent approximately 10 acres of a similar soil type and should consist of at least 20 individual soil cores. Soil probes, which are steel tubes about one-inch in diameter, are commonly used to extract soil cores. Each core should be taken to a depth of between six to 12 inches. Place soil cores in a bucket and thoroughly mix. Place about a quart of mixed soil in a plastic bag and seal it to inhibit drying.

Caring for Soil Samples: Soil samples require special care to assure survival of the living nematodes in the soil. Laboratory information on a dried soil sample will not accurately reflect the true field condition.

  • Handle each nematode soil sample like a carton of milk.
  • Keep the sample cool, but not frozen. During collection of samples, keep them in an ice chest in the shade.
  • Transport samples in a pre-cooled ice chest to prevent overheating.
  • Deliver samples to the diagnostic laboratory as soon as possible. Use overnight delivery if possible.

Provide Diagnostic Laboratory with All Pertinent Information about the Situation:

  • Current crop, past crop, intended crop, date of sampling, location, grower name.
  • Description of all specific problems. List nematode(s) suspected in the area.
 
State Nematode Diagnostic Laboratories for Soil Sample Analyses:

(For costs of analyses, contact the laboratory or your county agent).

Alabama

The Plant and Nematode Diagnostic Laboratory
101 Extension Hall
Auburn University
Auburn, AL 36849

Arkansas

Nematode Diagnostic Laboratory
Southwest Research and Extension Center
362 Highway 174 North
Hope, AR 71801

Arizona

M. A. McClure
Department of Plant Pathology
University of Arizona
204 Forbes Building
Tucson, AZ 85721

California

For the commercial laboratory nearest you, contact your local University of California Cooperative Extension Office.

Florida

Nematode Clinic
Attn: Robert Dunn
Department of Entomology & Nematology
University of Florida
Gainesville, FL 32611

Georgia

University of Georgia
Nematode Assay Laboratory
Plant Pathology Department
4 Towers Building
4 Towers Road
Athens, GA 30602-4356

Louisiana

Nematode Advisory Service
Louisiana State University
302 Life Sciences Building
Baton Rouge, LA 70803-1900

Mississippi

Extension Plant Pathology Department
Mississippi State University
P.O. Box 5446
Mississippi State, MS 39762

Missouri

Nematode Assay Laboratory
University of Missouri
103 Waters Hall
Columbia, MO 65211

New Mexico

Leyendecker Plant Science Research Center
New Mexico State University
Las Cruces, NM 88003-0003

North Carolina

Attn: Jack Imbriani
North Carolina Department of Agriculture
Agrinomic Division
Nematode Advisory Service
4300 Reedy Creek Road
Raleigh, NC 27607-6405

South Carolina

Nematode Assay Laboratory
Clemson University
Cherry Road
Clemson, SC 29634

Tennessee

Mr. T. S. Stebbins, Laboratory Diagnostician
Tennessee Plant Diagnostic Center
5201 Merchant Drive
Nashville, TN 37211-5201

Texas

Plant Disease Diagnostic Laboratory
Plant Pathology Department
Texas A&M University
120 Peterson Hall
College Station, TX 77843-2132