COLUMBIA, Mo. - The soybean cyst nematode, the No. 1 pest in soybeans, is likely to remain so, according to the results of a five-year study in the Midwest and Canada, a University of Missouri extension nematologist said.

"We've looked at soybean genotype, tillage, row spacing, soil nutrients and plant nutrients and their effects on soybean cyst nematode population and dynamics in the Midwest and in Ontario, Canada," said Pat Donald, MU plant microbiologist and pathologist who was the principal investigator for the study.

The North Central Soybean Research Program sponsored the study, which was partially funded by the United Soybean Board. Researchers examined SCN management practices at nine locations.

"We found that in five states, including Missouri, the yield of SCN-resistant varieties was greater than the yield of susceptible varieties. In two states, it really didn't make a difference, but generally, the nematode reproduction was lower in resistant soybeans than in susceptible soybeans."

At all the locations, the researchers examined the effects of 7-inch, 15-inch and 30-inch spacing. "Only in Ontario did row spacing affect SCN populations," Donald said. "As we narrowed the rows, we'd have greater root volume and more food for the nematode. Their reproduction is related to the food they have." Yield, however, was higher with the narrower rows in the short term, she said.

No-till management, long believed to be an effective management tool for soybean cyst nematode, did not appear to make a drastic difference, Donald said. "The effects of tillage on yield and soybean cyst nematode were inconsistent throughout the region. We can't determine unequivocally that no-till reduces SCN populations."

All the test plots were planted in a yearly corn-soybean rotation. Researchers measured different nutrients in the soil and plants, Donald said. "In terms of soil and plant nutrients, those that were most consistently involved with yield and SCN reproduction were iron, zinc, magnesium and potassium." At some locations, shortages of these nutrients appeared to make the plants more vulnerable to the pest. "They're already stressed, and then they have the nematode."

One strategy did appear to make a difference at all the locations, Donald said. "If you have SCN, you should be growing resistant soybean varieties." However, "the producers need to be out checking their fields. There are too many variables. They can't just plant resistant varieties, do no-till and expect minimum yield loss."

She said sampling fields every year for SCN populations before planting provides a full and accurate record of which management strategies work best in which field.

Donald said the researchers originally were charged with finding ways to get rid of the pest altogether, but the study indicates that might not be possible. "The soybean cyst nematode is way too adaptable to be eliminated with our current management strategies."