A lot of soybeans that farmers have thought to be resistant to soybean cyst nematodes are not proving to be up to the task of resisting SCN, according to soybean breeders and researchers.

This situation means that many soybean farmers don’t realize their fields have become a buffet for soybean cyst nematodes (SCN), despite the use of SCN-resistant soybean varieties. University research and Extension soybean specialists see a need for educating farmers on what to do other than plant what they think are SCN resistant soybeans.  

These microscopic, parasitic worms lurk beneath the soil and can feed off soybean plant roots for some time, before any above-ground crop damage is noticed. By then, the SCN population has grown much more numerous and stronger, becoming difficult to control as well as a huge economic threat to soybean farmers.

“In recent years, an increase in aggressive SCN populations, which can feed and reproduce on resistant varieties, has been widely documented throughout the north central U.S.,” said Sam Markell, Ph.D., associate professor and Extension plant pathologist at North Dakota State University.

Soybean farmers are used to selecting a resistant variety and assuming SCN will be managed in their field. Most are totally unaware of the slow-moving disaster posed by the changing pathogen.

A survey of 1,100 soybean farmers across 17 states, conducted in late 2015, identified SCN as one of the biggest foes of soybean crops. Of those surveyed, 63 percent indicated they were growing SCN-resistant soybean varieties, while the majority of respondents knew only “a little” or “nothing” about SCN. Worse yet, 66 percent were not scouting or sampling for SCN.

Syngenta collaborated with five land-grant universities to design the survey, following their July 2015 meeting to dissect the biology and manage SCN. Other findings from the survey showed:

  • 60 percent who grew SCN-resistant soybeans were growing them on all soybean acres
  • 68 percent who grew SCN-resistant soybean varieties didn’t know the source of resistance in the varieties
  • 69 percent of growers didn’t think SCN-resistant varieties were less effective today than in the past, contrary to widespread evidence of SCN populations adapting to genetic resistance

“Using the same source of resistance for more than 25 years has reduced the efficacy today, in a similar way as if we used the same herbicide over and over again,” said Greg Tylka, Ph.D., professor and Extension nematologist at Iowa State University.

The SCN populations are changing all around the country, but the way we manage SCN is not. “We are on the front end of a crisis similar to herbicide-resistant weeds and even costlier to farmers,” said Shawn Conley, Ph.D., professor and Extension agronomist at University of Wisconsin-Madison. “From an agronomic point of view and to keep productivity high, this is alarming.”