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,” Tylka says. “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.

“Sandy soils almost always experience more SCN damage because they drain quickly and don’t hold nutrients very well. Poor soil moisture and nutrient deficiencies stress the soybean plants, making them more vulnerable to damage from SCN feeding.” 

“SCN egg numbers also tend to be greater in higher-pH soils,” Tylka says. “Experiments in Iowa, Michigan, Wisconsin and Minnesota have shown that as pH increased across fields from 5.5 to 8, SCN populations increased too.”