If you want to manage soybean cyst nematode — Iowa’s biggest soybean yield robber — you need to plant soybean varieties resistant to this pest. Soybean varieties that are resistant to SCN are essential tools for controlling this tiny troublemaker, a microscopic worm that infests 78% of the fields in Iowa. That’s according to a 2016 survey conducted by the Iowa Soybean Research Center at Iowa State University.

Not all SCN-resistant soybean varieties are created equal, however. 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, says ISU Extension plant pathologist and nematode expert Greg Tylka. Thus, SCN control can vary greatly among resistant soybean varieties, just as yield can and does vary.

ISU evaluates the SCN control and yield of SCN-resistant soybean varieties in field experiments conducted at various locations throughout Iowa each year. The effort is supported, in part, by soybean checkoff funds from the Iowa Soybean Association.

Soil sample processing and overall data analysis for the experiments in 2016 were completed in mid-December, says Tylka. More than 150 glyphosate-resistant, SCN-resistant and 24 LibertyLink, 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 now available online. The publication Evaluation of Soybean Varieties Resistant to Soybean Cyst Nematode in Iowa-2016, IPM 52, is available for free.

New format for variety test report
To make the information more easily viewed and used, presentation of the results is streamlined for 2016, says Tylka. The SCN-resistant varieties are shown in descending order of yield, and yield is depicted with bars on the right side of the page in the report.

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, Tylka explains.

Greater yields and lower SCN numbers
Soybean yields were greater in the 2016 experiments than in 2015, and SCN population densities were variable among the experimental locations, notes Tylka. Overall, the mean or average 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. 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, and the numbers varied among resistant varieties as well.

More information available on how to manage SCN
Tylka cautions soybean farmers that 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.

He encourages farmers to seek out and consider other sources of yield trial information and data on SCN control for SCN-resistant soybean varieties. And if possible, evaluate several SCN-resistant varieties at your own location in Iowa to determine the best varieties for your local conditions.

More information about the biology and management of SCN is available at soybeancyst.info and soybeanresearchinfo.com.