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The widespread drought made 2012 a banner year for SCN in Iowa. “In 25 years I’ve never seen as much reproduction as we did last year,” says Greg Tylka, Iowa State University (ISU) Extension nematologist and plant pathologist. “We don’t understand exactly why SCN seems to thrive when it’s dry, but we also know that nematodes grow best in the greenhouse under dry conditions. “
Conversely, the 2013 growing season began in Iowa with record rains, delaying soybean planting. “But by June 2,” Tylka says, “SCN females were reported on soybean roots in sandy soils just 26 days after planting. In a normal spring, we expect to see female nematodes 40 days after planting.
Very often, the only visible sign of soybean cyst nematode is an egg sac on soybean roots.
Life after SCN
“An SCN infestation is not a death sentence,” Tylka says. “Finding it doesn’t mean you have to stop growing soybeans, you just have to manage it. “
Prevention is critical for long-term SCN control. “If you can catch it when populations are relatively small, it is much easier to keep low numbers low than to bring high numbers down.
“If you discover SCN in a field, start managing it with resistant varieties, crop rotation and seed treatments,” Tylka says.
“If results of an HG type (formerly called the SCN race test) reveal that you have SCN with increased ability to reproduce on soybeans with the PI 88788 or Peking sources of resistance, it’s advisable to plant soybeans with a different source of resistance,” Tylka says. “Unfortunately there are not too many available. Out of 771 varieties in the 2013 Iowa State SCN resistant-variety list, 755 of them had PI 88788 resistance.”
New nematicides and seed treatments, including Avicta, Votivo and N-Hibit, have come to market recently to help bolster SCN management programs early in the growing season.
In 2014, Syngenta plans to commercialize a biological seed treatment for SCN in its new Clariva Complete Beans. (See sidebar) The seed treatment uses a living, natural parasite of SCN– Pasteuria nishizawae --to kill the pest. “We’ve known for a long time that it is effective against SCN,” Tylka says, “but it remains to be seen whether it will colonize in the root system for season-long control.”
“SCN is almost universally the No. 1 soybean disease in the nation,” Tylka says. “But as other ‘sexier’ challenges — like SDS or soybean aphid — have arisen, a lot of people seem to have let down their guard about SCN.”