Soybeans planting is just weeks away, and it is important that you test your fields for soybean cyst nematodes (SCN) now before planting. SCN is a major concern to growers throughout the state. These parasitic round worms invade the plant roots and suck nutrients from the plants, decreasing their ability to produce adequate yields. The challenge with preventing SCN is that infected plants do not easily express symptoms. Fields can sustain up to 30% yield loss due to SCN without displaying any symptoms, making sampling the only way to identify a problem that you might not actually be seeing. Producers often ignore the possibility of SCN because they plant resistant varieties, but it is important to realize that SCN can adapt to the resistance lines if the same source is used year after year. Amanda Howland, the new coordinator for the MU Extension Plant Nematology labs, says 97% of the soil samples received since January 1, 2015 tested positive for having SCN, with egg counts ranging from 100 to over 35,000 eggs per cup of soil (250 cc3). Roughly 25% of the total samples tested had more than the threshold value of 10,000 SCN eggs/cup of soil. This proves it is important to sample soybean fields and check SCN egg counts periodically (every three years) to monitor whether the egg counts are increasing. Although typically fall is a good time to check fields for SCN because the results will be available for use in making decisions and plans for the next growing season, especially in terms of crop rotation and soybean variety selection, it is still not too late to sample the fields now ahead of planting.
Since SCN egg counts are only as good as the sample taken, here are a few tips for sampling for SCN:
- Limit the size of the area being sampled: 10 - 20 acres is a good target.
- Using a bucket and probe or shovel, walk the area in a W or Z pattern, sampling about 8 inches deep in the root zone between the rows. Take about 20 cores (with a shovel take ¼ cup of soil from near the shovel tip). Mix the cores well into a composite sample, and bag about a pint of it for submission. Do not let samples dry out! Nematodes are sensitive to heat. Do not leave samples in the sun or other areas of high temperature.
- Label the plastic bag and ship it as soon as possible.
- Fill out a submission form (available from our Website or your local extension agent) or on a piece of paper indicate:
- Name, address, phone, and email (if you have email, results can be sent quickly)
- County and cropping history
- Type of test: SCN egg count ($20), HG Type test modified (In state: $75; Out of state: $125) or full (In state: $100; Out of state: $150), or Complete Nematode Analysis which includes plant parasitic nematodes identification ($30)
- The mailing address for the lab is: Plant Nematology Lab, 23 Mumford Hall, University of Missouri, Columbia, MO 65211.
The SCN Egg Count test is what most soybean growers would need. If you notice a field that is slipping in yield, had high egg counts years ago, or you haven't had your soils tested for SCN in the last three years, a $20 SCN Egg Count test is a worthwhile investment that can offer peace of mind and save considerable yield loss.
The HG Type test would be for the grower who has high egg counts after growing resistant lines for years. This test indicates the HG type (or race) of SCN in the field, and what sources of resistance would be good to choose when buying seed.
The Complete Nematode Analysis test is a count of all the plant parasitic nematodes in the sample. (It does not give an SCN egg count.) This test is used if you feel you may have a nematode problem other than SCN. This test would also be important for growers in SE Missouri who may have the Root Knot nematode as well as SCN.
The Extension Nematology Lab has a website with more information on how to sample, the tests we provide, and how samples are analyzed in the lab. A submission form can also be downloaded from the site http://soilplantlab.missouri.edu/nematode. The turnaround time for the lab is typically 3-5 to working days.
For management decisions regarding SCN please refer the University of Missouri Extension Guide on Soybean Cyst Nematode: Diagnosis and Management. This guide can be downloaded at: http://extension.missouri.edu/publications/DisplayPub.aspx?P=g4450