Now and this fall is a good time to take soil samples for SCN (Soybean Cyst Nematode). SCN is a serious “chronic” problem in soybean fields in south central Minnesota. Research has shown yield losses of 15 to 30% on susceptible varieties. The best way to tell if a soybean field has SCN is through soil testing. Even though there are some resistant varieties, they are not grown in every field. Resistance and rotational management have to be used together to decrease the SCN infestation in fields with high levels of SCN.

Plants infected with high numbers of SCN have poorly developed root systems that cannot utilize nutrients and water efficiently. The result may be stunted plants with chlorotic (yellow) foliage. However if soybeans are grown on fertile conditions without other soil and weather stress, the only symptom may be lower yields. Seed yields are low because fewer pods develop on infected plants. SCN infections by themselves do not reduce seed size, number of seed per pod, or seed quality.

What Is A Soybean Cyst Nematode?

Soybean Cyst Nematode is a microscopic roundworm that attacks roots of soybean, dry beans, crimson clover and snap beans. Developmental stages include the egg and four juvenile stages. The first juvenile develops within the egg and molts to form a second-stage juvenile (J2). The J2 hatches from the egg, moves through soil pores in the film of surrounding soil particles, is attached to actively growing roots, and infects by penetrating host plant roots near the root tip. After penetrating the root, the nematode establishes a feeding site in the vascular tissue, enlarges to become sausage-shaped, and molts three more times before becoming an adult. The adult is lemon-shaped and, when fully developed, is visible on the root surface. The adult male undergoes a metamorphosis during the last molt to become a slender, motile worm. The male stops feeding and exits the root.

A pheromone released by the female attracts the male for mating. The female exudes a gelatinous matrix from the posterior portion of its body into which it deposits a small portion of the total eggs that it will produce. Eggs in the egg mass hatch and the resulting larvae infect soybean roots. Several hundred additional eggs are retained inside the female body. As the female ages it changes color from white to yellow. When the female dies, the body (now referred to as the cyst) becomes dislodged from the root and changes to a dark brown color. The eggs that come from the cysts are what are counted by a testing laboratory to determine the level of economic infestation.

Life Cycle Duration:

In southern Minnesota the nematode can complete only three to four generations with each generation lasting approximately 3 to 4 weeks.

Sampling For SCN Guidelines:

• Soil samples can be collected from early spring to late fall, but best in late summer or fall in corn & soybeans.
• 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 the affected area because these plants usually have severely stunted root systems that cannot support SCN. Thus resulting 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).

University of Minnesota SCN Management Guidelines:

Listed below are guidelines for determining what management practices farmers should follow to decrease SCN infestation levels based on soil sample results from a nematode testing lab:

Less than 200 eggs/100 cc (cubic centimeters) of soil: Plant a susceptible variety

200-2000 eggs/100 cc: 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: Resistant or susceptible variety should not be planted. (Follow rotational management guidelines listed below).

Rotation Management Strategies If SCN Detected:

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 Year 2 variety)

Year 5 – Corn or other non-host crop

Year 6 – Susceptible soybean variety

Summary:

Anything that moves soil will move SCN with it: wind, water, migratory birds, tillage, harvest equipment and soil peds in seed stocks. Once introduced into a field, SCN may take about 10 years to build up to a damaging level; depending on how often susceptible soybean is grown. A new publication from the Plant Health Initiative (North Central Soybean Research Program) funded by soybean check off dollars is now available. Consult the web address www.planthealth.info for more information and an opportunity to view the publication on-line

SCN Testing Labs in South Central Minnesota:

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

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

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