Test your soil to find out if and what type of potato nematodes are in your field. Many of these nematode lab websites contain useful information for growers on proper soil sampling, along with sample submission forms for the diagnostic clinic or lab.
Iowa State University: Plant and Insect Diagnostic Clinic
Kansas State University: Extension Plant Pathology - Diagnostic Lab
MSU Plant & Pest Diagnostics, Center for Integrated Plant Systems (CIPS)
East Lansing, MI
North Dakota State University: Department of Plant Pathology/NDSU
Ohio State University: Soybean Pathology and Nematology Lab
University of Illinois Plant Clinic
University of Missouri: Soil and Plant Testing Laboratory
University of Nebraska: Nematode Diagnostic Lab
Waters Agricultural Laboratories, Inc. (Georgia)
Waters Agricultural Laboratories, Inc. (Kentucky)
Waters Agricultural Laboratories, Inc. (Mississippi)
Waters Agricultural Laboratories, Inc. (North Carolina)
Western Laboratories, Inc.