How To Pick A Soybean Variety When Soybean Cyst Nematode Is Present

DR. PAT DONALD

JACKSON, TENN.
   Soybean cyst nematode (SCN) is found generally wherever soybeans are grown. It is one of the most consistent yield-limiting pests in soybean production. Improved soybean varieties however, often mask the symptoms of stunted chlorotic plants described when this pest was first found. Lack of above-ground symptoms does not mean that damage in the form of yield loss is not present. Often slight yield loss can occur each year as the population builds under favorable conditions. Surveys of Tennessee soybean fields for the presence of SCN have been ongoing for more than the last 10 years, supported in part through funding by the Tennessee Soybean Promotion Board. The results of these samples have shown that SCN is present at a detectable level in slightly less than 50 percent of Tennessee soil samples. Some of these fields had stunted chlorotic plants and significant yield loss in spots of the field.
   In addition to collecting soil samples, we have been characterizing the SCN populations from these fields when the SCN level is high enough to allow testing. In general, Tennessee SCN populations characterized as race 1, 2, 3, or 5. In general race 3 populations were only found in middle and eastern Tennessee. This finding is similar to other southern states where race 3 populations can no longer be found in more long-term intensive soybean production fields areas. In west Tennessee race 2 was found most commonly followed by race 5. These characterizations were conducted in the greenhouse and included HG Type testing. The most common HG Type for Tennessee SCN populations was 2.5.7.
   The bottom line is how to pick a variety that performs well when SCN is known to be present and the characterization of the SCN population is known. It is important to know if the SCN level in each production field where SCN has been detected is increasing.  Soil sampling is the only way to catch the problem before extensive yield loss is present. Contact your local extension office or click on the following links for procedures to sample soil and/or where to send soil samples for SCN analysis. The majority of commercial soybean varieties still contain PI 88788 as the main or only source of resistance to SCN. This source of resistance continues to work in many soybean production fields. However, in some fields the SCN population level that can reproduce on PI 88788 is high and the reproduction of most Tennessee SCN race 2 populations is much higher on PI 88788 than SCN populations in the Midwest. The best way to determine the best variety for your situation is to conduct on-farm tests of different varieties. Soybean varieties to include should contain lines that do well in the University of Tennessee Variety Trials in your location. Not all varieties with PI 88788 as a source of SCN resistance exhibit the same reaction to SCN. Consideration should also be given to other pests present in your location and potential resistance to them that is commercially available. If you have used SCN resistant varieties and have a high level of SCN in the soil, you may need a race 2 resistant variety. Contact your seed dealer and ask for lines with that resistance. SCN resistance in soybean varieties can be found at UTcrops.com within the UT Variety Trial Data and Soybean Disease Rating Summaries (2013 variety trial data will be available by the end of the year).∆
DR. PAT DONALD: Adjunct Professor, UT Entomology and Plant Pathology, University of Tennessee