SCN-resistant soybean varieties are not immune from pest

SCN-resistant soybean varieties are not immune from pest

Like herbicide resistant weeds, the looming SCN crisis will not be averted if action isn't taken.

Many soybean farmers don’t realize their fields may be a buffet for soybean cyst nematodes (SCN), despite the use of SCN-resistant soybean varieties.

Iowa State University Extension nematologist Greg Tylka says these microscopic, parasitic worms lurk beneath the soil and can feed off soybean plant roots for some time, before any aboveground 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.

TAKE NOTE: Soybean growers should heed lessons from the herbicide-resistant-weed issue, says ISU’s Greg Tylka. Soybean cyst nematode is a pest that is changing. Many farmers know little to nothing about it. The problem is too big for one farmer, one company or one state university to manage it alone.

“In recent years, an increase in aggressive SCN populations, which can feed and reproduce on SCN resistant bean varieties, has been widely documented throughout the north central U.S.,” says Sam Markell, 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.

Survey shows 66% of farmers don’t scout or sample soil for SCN

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% indicated they were growing SCN-resistant soybean varieties, while the majority of respondents knew only “a little” or “nothing” about SCN. Worse yet, 66% 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% who grew SCN-resistant soybeans were growing them on all soybean acres

* 68% who grew SCN-resistant soybean varieties didn’t know the source of resistance in the varieties

* 69% 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 variety resistance for over 25 years

“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,” says Tylka, the ISU Extension nematologist. His colleagues at other universities agree.

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,” says Shawn Conley, Extension agronomist at University of Wisconsin-Madison. “From an agronomic point of view and to keep productivity high, this is alarming.”

Like herbicide resistant weeds, the looming SCN crisis will not be averted if everyone doesn’t come together for a common goal. “It’s going to take a group effort like the ‘Resistance Fighter’ campaign from Syngenta for herbicide resistance to prevent an even larger crisis with SCN,” says Seth Naeve, Extension agronomist at University of Minnesota.

How can you protect the effectiveness of SCN-resistant beans?

With Resistance Fighter, Syngenta and key universities were joined by grower groups in an urgent effort to educate farmers, as well as seed and herbicide suppliers, how to manage and delay the looming threat of herbicide resistance. Diversity was the key to success. “The time is right to do something similar for SCN,” says Palle Pedersen, head of Seedcare product marketing for Syngenta. “We are standing at the edge of a cliff right now and none of our tools can do it alone.”

To preserve the effectiveness of SCN-resistant varieties, Pedersen recommends farmers implement a multipronged solution that includes technologies like seed treatments, with a completely different mode of action. “We know what happens when only one mode of action is used to manage weeds, so let’s not head down that road and hit those same potholes,” says Pedersen.

More research is underway to document the importance of using alternative solutions to slow down the development of SCN resistance. To learn more visit and Follow on Twitter at

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