The soil sampling time for soybean cyst nematode (SCN) detection can be carried out at any time, but to obtain a representative result, sampling should be conducted in the fall, immediately after 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.
We always recommend fall harvest soil sampling in our lab for proper SCN detection.