Soybean varieties that are resistant to the soybean cyst nematode (SCN) are essential tools for managing the pest. Resistance to SCN requires multiple genes, and soybean varieties bred to be resistant may not contain all of the resistance genes necessary to provide maximum nematode control. Consequently, SCN control can vary greatly among resistant soybean varieties, just as yield.
Iowa State University evaluates the SCN control and yield of SCN-resistant soybean varieties in field experiments conducted throughout Iowa annually. The effort is supported, in part, by soybean checkoff funds from the Iowa Soybean Association.
2016 results now available online, coming in print
Soil sample processing and overall data analysis for the experiments in 2016 were completed in mid-December. More than 150 glyphosate-resistant, SCN-resistant and 24 Liberty Link, SCN-resistant varieties were included in experiments across northern, central, and southern Iowa.
Several SCN-susceptible soybean varieties also were included in the experiments for comparison. Four of the SCN-resistant varieties had the Peking source of resistance; all other resistant varieties had the common, PI 88788 source of resistance.
A report of the 2016 results is available online here. The report also is available for free download at the ISU Extension Store, Evaluation of Soybean Varieties Resistant to Soybean Cyst Nematode in Iowa-2016, IPM 52. Hard copies of the report will be mailed as a special insert in the Iowa Farmer Today and the Illinois Farmer Today magazines on January 14, 2017.
New format for 2016 report
To make the information more easily viewed and used, presentation of the results was streamlined for 2016. The SCN-resistant varieties are shown in descending order of yield and yield is depicted with bars on the right side of the page, as shown in Figure 1 with results from the experiment in east central Iowa with glyphosate-resistant varieties.
To the left of yield data are mean end-of-season SCN numbers (population densities) and blue bars showing the SCN reproductive factor (RF) for each variety. The RF value is the change in SCN soil numbers from planting to harvest.
End-of-season SCN numbers and RF values illustrate the amount of SCN control provided by the varieties. Data on the susceptible varieties in the experiment are shown at the bottom of the page.
Greater yields and lower SCN numbers with resistant varieties
Soybean yields were greater in the 2016 experiments than in 2015 (described here), and SCN population densities were variable among the experimental locations. Overall mean yields of the resistant varieties were greater than the susceptible varieties in all but one of the experiments, in which the mean yields were the same (Figure 2).
Yields of individual resistant varieties varied by 10 to 35 bushels per acre in individual experiments. End-of-season SCN numbers were lower for SCN-resistant soybean varieties than susceptible varieties at all locations (Figure 3), and the numbers varied among resistant varieties as well.
More information about SCN
These data are from a limited number of locations and should be used only as a beginning point for developing a SCN management program for any specific field. Performance of individual SCN-resistant soybean varieties in SCN-infested fields will vary among locations and years.
Farmers are encouraged to seek out and consider other sources of yield and SCN control data for SCN-resistant soybean varieties and, if possible, to evaluate several SCN-resistant varieties at their own locations to determine the best varieties for their local conditions.
More information about the biology and management of SCN is available here and here. Iowa State University’s management recommendations for SCN are available online in a downloadable format, Soybean Cyst Nematode (SCN) Management Recommendations, IPM 63.