The soybean cyst nematode (SCN) is a serious and widespread problem in soybean fields in southern Minnesota that is spreading north. SCN can upset the function of roots, cause yellowing and stunting of plants, and result in yield losses of 15 to 30% on susceptible varieties. Soybeans grown under good growing conditions may not show symptoms even though they can be heavily infected with SCN and suffer yield losses. Three keys to understanding and managing this pest are planting resistant varieties, rotation, and soil sampling to detect presence and levels of SCN infestation.

Variety Selection

Resistant soybean varieties can provide a substantial yield benefit in fields infested with SCN, but selection of the best resistant varieties can also be challenging. Dr. Jim Orf, Professor of Soybean Breeding and Genetics at the University of Minnesota, suggests that producers should ask seed dealers several questions when they consider new SCN resistant varieties or varieties that are not in the University Variety tests.

• Ask for variety data from sites with SCN in Minnesota or greenhouse tests that used soil or SCN populations from Minnesota. SCN population types may vary from state to state, and resistance in one state may not be as effective in other states.
• Ask about the source of the SCN resistance.
• Ask for data from both SCN infested and non-infested fields in Minnesota.
• Ask about level of resistance or the FI (female index). The FI is a measure of how many cysts develop on a variety compared to a standard control variety. A high FI indicates a low level of resistance, whereas a low FI indicates a high level of resistance.
• Ask for data on Pf/Pi from field sites. This ratio of the final egg count divided by the initial egg count will indicate the level of reproduction of SCN on specific varieties, and will provide a measure of resistance. Generally, varieties with low Pf/Pi ratios will have high levels of resistance and will limit the increase of SCN numbers in soil.

Sampling and Detection of SCN

In addition to searching for soybean varieties with SCN resistance, this fall is a good time to samples fields for SCN that will be planted to soybean in 2006. Soil testing can be used to tell if a soybean field has SCN, and to obtain the level of infestation. During the summer, fields can be surveyed for the presence of SCN by digging up plants and looking for cysts on the roots.

Guidelines for Sampling for SCN:

• Soil samples can be collected from early spring to late fall, but fall after harvest is an excellent time to collect samples for fields that will be planted into soybean the following year.
• Collect a core or ¼ cup from 20 different locations within an area no larger than 10 acres in order to reduce variability of testing results.
• Sample the area in a zigzag pattern. Collect soil at a depth from 0 to 8 inches. In soybeans take from the root zone (not between the rows).
• Do not collect the sample from the center of affected areas because these plants usually have severely stunted root systems that cannot support SCN. This can result in low numbers when in fact the field may have higher numbers on average.
• Send 1 pint of soil from mixed sub-samples in plastic or paper soil test bags (if the samples will not be sent to the lab immediately than place them in the refrigerator or freezer until ready to ship so the eggs do not hatch).

Management Guidelines for SCN:

Guidelines for determining management practices to decrease SCN infestation levels based on soil sample results from a nematode testing lab:

• 1-2000 eggs/100 cc (cubic centimeters) of soil: Plant a resistant variety
• 2000-10,000 eggs/100 cc: Resistant variety recommended but yield loss may still occur.
• More than 10,000 eggs/100 cc: Do not plant soybean; plant corn or other rotational crop using rotational management guidelines listed below.

Crop Rotation Strategies When SCN is Detected in a Field:

• Year 1 – Corn or other non-host crop such as small grain or alfalfa
• Year 2 – SCN Resistant Variety
• Year 3 – Corn or other non-host crop
• Year 4 – SCN Resistant Variety (use a resistant source different than used in Year 2 if available, otherwise, use a different variety with the same source of resistance)
• Year 5 – Corn or other non-host crop

Summary:

The SCN is a microscopic roundworm that attacks roots of soybean. Juvenile nematodes attach to actively growing roots and penetrate near the root tip. The female nematodes then establish a feeding site in the vascular tissue and enlarge to ultimately become a lemon-shaped visible cyst on root surfaces that is filled with eggs. As the female ages it changes in color from white to yellow to brown. In southern Minnesota the nematode can complete three to four generations per season with about 3 to 4 weeks per generation.

SCN SOIL TESTING LABS in South Central Minnesota:

University of Minnesota
Nematology Lab
Southern Research and Outreach Center
35838 120 th Street
Waseca, MN 56093-4521
507-837-5649

AGVISE Laboratories
902 13th Street North
Benson, MN 56215
320-843-4109

MVTL Laboratories
326 Center Street
New Ulm, MN 56073
800-782-3557

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