“SCN is the ultimate pathogen,” says Greg Tylka, Iowa State University (ISU) Extension nematologist and plant pathologist. “It causes yield loss directly and indirectly by making other things, like soybean sudden death syndrome (SDS) and soybean brown stem rot (BSR), worse. We don’t know completely how it works, but it is a very consistent relationship,” Tylka says. “SCN has a unique biology that makes it very difficult to control. High reproductive capability, genetic diversity and variable responses to different cultural practices and control methods all contribute to it being the leading cause of soybean yield loss.”

SCN populations build rapidly because females’ very large ovaries enable them to lay several hundred eggs at a time, Tylka says. “Its fairly short lifecycle allows four or five generations to occur in one season.

“SCN females mate with many different males, providing tremendous genetic diversity,” Tylka says. This impedes resistance management because SCN can respond differently to various control methods. The genetic diversity is one of the reasons that SCN has been able to reproduce on soybean varieties with the PI 88788 and Peking sources of SCN resistance.”

And SCN has the unique ability to live in dormancy for 10 or more years without food, Tylka says. “Many farmers have infested fields and do not know it’s there. Infestations can increase undetected for five to 10 years. Soybean yields decrease steadily but the plants don’t look sick.”