The time for sampling for soybean cyst nematode is critical for proper SCN detection and subsequent management decisions.
Sampling during a wrong period or season will result in an inaccurate estimate of SCN population density and can lead to wrong management decisions.
To avoid this, soybean growers should conduct sampling for SCN during the right sampling windows.
Although, SCN can be detected in infested fields any time of the year, to obtain an accurate population estimate, SCN sampling should be conducted in the fall, immediately after soybean harvest.
Fall harvest is the best sampling period for SCN because most of the cysts and white females are viable and healthy during the fall period. This makes them easily recoverable during the extraction process. Samples collected in the fall will give a nematode density number that best represents the actual density of SCN in the field, unlike samples collected later from frozen wintry soil or during the early spring planting period.
In winter samples, most SCN cysts are now brown in color, and dead. So during the extraction process, they stay afloat with soil debris. They are easily lost in debris because they are difficult to separate from the debris.
In spring samples, most of the SCN are no longer in cyst form. Most of the eggs have hatched into juveniles and are free in the soil. Extracting the juveniles from soil requires a special extraction procedure that is different from the one used for extracting cysts. So the juveniles are mostly not accounted for when counting only eggs in samples. The number of eggs recovered from spring samples usually does not represent the actual number of nematode density in the soil – since the juveniles are not counted.
To ensure a proper SCN population estimate, growers should collect samples during fall or early winter when most of the SCN populations are in viable and detectable form.