Almost 2 bu./acre were gained in the better SCN-resistant varieties tested by Iowa State University (ISU). ISU's Soybean Variety Trial program evaluated many of the hundreds of SCN-resistant varieties for agronomic performance and for nematode control at numerous locations in Iowa.

The tests show that SCN-resistant varieties can suppress SCN reproduction and provide increased soybean yields compared to susceptible varieties.

Currently, there are three main genetic sources for SCN resistance genes in commercial soybean varieties: PI 88788, Peking and PI 437654 (also known as Hartwig and PUSCN14 resistance, the latter also known as CystX resistance).

Each of these sources of SCN resistance contains several genes that confer resistance. Consequently, soybean varieties developed from these various sources may not all contain the same genes in the same combinations. All of these sources of SCN resistance allow limited reproduction of only a few soybean cyst nematodes.

Resistant varieties must be used in an integrated management program, along with the use of nonhost crops and scouting for early detection of SCN, to maximize yields and minimize pest reproduction long term.

“SCN population densities increased 2- to 15-fold on susceptible varieties but were kept in check or even decreased a little with the SCN-resistant varieties,” says Greg Tylka, ISU research and Extension nematologist who oversees the variety evaluations. “But our 2006 trials again show that not all SCN-resistant soybean varieties are the same — in terms of yield and also in terms of nematode control.”

End-of-season SCN population densities were significantly greater in plots where susceptible varieties were grown compared to plots planted with resistant varieties.

Unfortunately high-yielding SCN-resistant soybean varieties do not necessarily keep SCN from increasing in number. “Once a field is infested with SCN, it is there forever,” Tylka says.

Growers are encouraged to evaluate several SCN-resistant soybean varieties at their own locations. The 2006 ISU SCN Trial results are on the Web at www.isuscntrials.info.