Sampling for soybean cyst nematode

Sara Bauder
Soybean cyst nematode female cysts on soybean roots. Each cyst can have more than 300 eggs.

Fall is the ideal time of year to test your fields for soybean cyst nematode.

Testing is a simple process that may save growers money in the long run. Testing can really take place anytime in any crop, but there is likely to be a higher and more detectable occurrence of SCN in the fall following a soybean crop.

Soybean cyst nematode is an often overlooked yield robber; in fact, it’s considered the most damaging soybean pathogen in North America with research showing that it can cause more than 40% yield loss in some cases. This pest can quietly sneak up on growers as it causes yield loss with no obvious above ground symptoms even in low level infestations.

SCN poses a threat to many growers and has been positively confirmed in many counties. This nematode attacks the root of the soybean plant, which in turn can pose a greater risk for other fungal pathogens to more easily infest the plant through open wounds.

SCN tends to be spread from field to field by equipment, erosion, wildlife, and other environmental factors. Once a field is infested with SCN, it is highly unlikely to eradicate it; however, reducing the population is possible.

If SCN is detected in a field, there are several integrated pest management practices that should be considered. Lengthening crop rotation (three crops or more) removes the host crop (soybean) for a longer period of time which can help to decrease SCN populations. Other options include purchasing SCN resistant soybean cultivars for any level of infestation and/or the use of nematicide seed treatments in heavy infestations — greater than 10,000 eggs per 100 cubic centimeters of soil.

Soybean cyst nematode lives in the top 8 inches of the soil, so when testing, use a soil probe or spade to take at least 20 top soil samples at an 8-inch depth in areas no larger than 15 to 20 acres. Field entrances, low-lying areas and fence lines are good areas to target. When sampling, angling the probe or spade into the soybean row is an ideal practice. Soil should be mixed well and placed in a soil sample bag.

Sampling fields every two or three years can help monitor populations (or lack thereof) and help explain yield losses in question. 

Fall Cover Crop Management

Another thing for many growers to consider this fall is cover crop management. Many producers have planted a cover crop following small grains and corn silage or into standing, maturing row crops. Cover crops can provide many benefits to growers including erosion control, nutrient cycling, increased water infiltration, weed control, additional forage, compaction relief, crop rotation diversification, etc.

Regardless of the purpose of your cover crop, there is great benefit in allowing it to winter kill or over-winter on its own. Tilling up cover crop fields in the fall defeats many of the benefits of cover crops as this opens soils for erosion all winter long, provides no soil cover for weed control in the spring, and speeds up vegetation breakdown rather than allowing nutrient capture to slowly breakdown in standing plants to potentially be available for the next cash crop.

Although it may be tempting to terminate cover crops manually this fall, allowing them to winter kill or (depending on the specie) over-winter and be terminated in the spring provides great benefits to the health of the soil and gives your investment more power in the long run.

Although we cannot always put a direct dollar amount on the benefits of cover crops to our soils, many research projects have shown yield bumps to cash crops as a result of the benefits cover crops provide.

Sara Bauder

Bauder is an agronomy field specialist for SDSU Extension