Soybean cyst nematode (SCN) has long been a challenge for soybean production in the U.S. This wormlike parasite is reaching economic levels in more fields, often without obvious symptoms. Soybean yield may be significantly reduced, and many growers may be unaware of the cause.
For effective SCN control, a combination of strategies is needed, including planting SCN-resistant soybean varieties, rotating crops and using seed treatments with a component for SCN control. A management program usually requires soil sampling to determine egg or cyst numbers and possibly SCN races. Monitoring SCN populations and races year after year can indicate if current practices are working or if further measures are needed.
In addition to planting SCN-resistant varieties, nematologists recommend rotating sources of resistance. DuPont Pioneer offers varieties with the Peking source of resistance, which can be rotated with the common PI 88788 source used in over 90% of current soybean varieties.
Previous research has shown that SCN can increase the severity of sudden death syndrome (SDS) symptoms and yield loss. More recently, DuPont Pioneer and Michigan State University examined the performance of Pioneer® brand soybean varieties with differing levels of resistance to SCN and SDS. This 2-year study was established in a field with heavy SDS pressure and HG type 2 SCN pressure.
Results showed that SCN reproduction differed significantly among varieties, as indicated by the Pf/Pi ratio (Pf = final SCN count; Pi = initial SCN count). SCN population did not increase on Pioneer® variety 92Y53 (Peking source of resistance), while a 17-fold increase in the SCN population was observed on Pioneer® variety 92Y51 (PI 88788 source of resistance). The varieties without genetic resistance to SCN had an SCN population increase of over 40-fold (Figure 1).
Figure 1. In the first year of a 2011-2013 DuPont Pioneer/University of Michigan study, SCN reproduction differed among varieties as indicated by Pf/Pi ratio (Pf = final SCN count and Pi = initial SCN count).
92Y53 had the best characteristic package of SCN and disease resistance for this environment and was the highest-yielding variety in both years of the study (Table 1). Pioneer® variety 92Y91, a non-SCN protected variety, had a relatively high disease index rating despite being moderately resistant to SDS. This finding supports previous observations that SCN can increase the severity of SDS symptoms and yield loss. In both years, yield was lowest with Pioneer® variety 92M82, which has low SDS resistance and no SCN resistance. Results showed that knowing the SCN population type and then matching the correct genetic resistance may help reduce SDS and SCN injury.
Table 1. SCN resistance and SDS score effects on soybean yields in a 2011-2013 DuPont Pioneer/Michigan State University study.
SDS was evaluated using a disease index (DX) rating. DX = (DS/9 * DI); where DS is disease severity using a 1-9 scale, and DI is disease incidence in 5% increments. *Values within a column followed by the same letter are not significantly different with 95% confidence.