Figure 1. Example of how to sample for SCN. Sampling for SCN can be done anytime provided the soil is not too wet and a soil probe can be pushed into the ground.
The prolonged winter conditions this spring have kept the soils too frozen/wet to sample for SCN. However, soil temperatures are now war and it is now a good time to sample fields for SCN, if weren’t sampled in the fall. Testing soil for SCN is important for two reasons: 1) to determine SCN occurrence and 2) to know the SCN population density within a field. This information can guide growers to determine management options. For fields where SCN has been detected before, periodic testing can indicate whether the SCN population density is increasing (i.e., management program is not working) or if the population density is decreasing (i.e., management program is working).
Why Test Your Soil?
One of the challenges in managing SCN is that it can cause up to 30% yield loss without causing obvious aboveground symptoms. In addition, SCN symptoms can sometimes be confused with those caused by other stress factors such as nutrient deficiency.
The most reliable method of determining the presence of SCN in the soil is through a soil test. Moreover, soil testing for SCN is free of charge to South Dakota producers, courtesy of the South Dakota Soybean Research and Promotion Council. Taking advantage of this service will help to get a better picture of the current SCN status of a field before planting soybeans this season.
To sample soil for SCN, use a soil probe or shovel and obtain 20 soil cores (Figure 1) ensuring areas such as field entrances, low yielding areas, and/or along the fence line are included (Figure 2). Larger fields should be divided into 10-20 acre sections. Sampling for SCN can be done any time provided the soil is not too wet (e.g., forms a paste when rubbed between the fingers) and not frozen so that a spade or soil probe can be inserted down to an 8” depth. Mix the 20 soil cores well and send (mail or dropoff) a minimum of one pint of soil to the SDSU Plant Diagnostic Clinic (address below) after filling out the SCN Sample Submission Form. This form needs to be included with the sample when it is submitted.
Figure 2. SCN sampling plan example. When sampling for SCN use a zig-zag pattern and include field entrance, low yielding areas, and low areas.
Soybean cyst nematode can be managed primarily through planting SCN resistant cultivars. Most of the SCN resistant cultivars have their source of resistance derived from PI88788, however, a few soybean cultivars with PI 548402, commonly known as Peking source of resistance, are available. Rotate between cultivars with different sources of SCN resistance to avoid SCN population adaptation to one source of resistance from developing. There are currently efforts in the region to continue to educate soybean producers about the importance of knowing their SCN numbers. The SCN Coalition website has more information of these efforts.
For fields with high SCN population (>10,000 eggs/100cm3 of soil), a longer rotation out of soybean (>2 years) is recommended. Nematicide seed treatments are available. However, results from small plot testing of nematicide products under field conditions has not produced consistent benefits. Any benefits from a nematicide are more likely when the field has a moderate to high SCN population (>6000 eggs/100 cm3 of soil).