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Research Highlights

Research Highlights
Evaluating Resistant Varieties and Seed Treatments in SCN Infested Fields

SCN-resistant soybean varieties are evaluated in field plots under real Iowa conditions so the state’s farmers get first-hand information about what they can expect. Photo: Greg Tylka

By Barb Baylor Anderson

The soybean cyst nematode (SCN) is Iowa’s most damaging soybean pathogen. Yield loss can cost Iowa farmers hundreds of millions of dollars or more annually. SCN has been found in all Iowa counties and up to 86 percent of Iowa fields. And its population densities can increase 10- to 50-fold in one growing season with survival for a decade or more without soybeans present.

Currently there are three primary options for managing SCN; growing nonhost crops such as corn, growing SCN-resistant soybean varieties or using nematode-protectant seed treatments. But research needs to take SCN management another step forward, says Greg Tylka, Iowa State University nematologist and principle investigator of the Iowa Soybean Association project.

“Field research conducted in this project can increase the competitiveness of Iowa soybean farmers through better and more sustained management of SCN,” he says. “SCN-resistant varieties and nematode-protectant seed treatments are being evaluated for agronomic performance and nematode control throughout the state. That information can help Iowa soybean farmers make soybean purchase decisions to maintain and improve yields.”

Tylka says the experiments conducted have been farmer-focused, applied research unique to Iowa. SCN-resistant soybean varieties are evaluated under real Iowa field conditions so Iowa farmers get first-hand information about what they can expect. Nematode-protectant seed treatment trials are coordinated with Iowa Soybean’s On-Farm Network to generate a robust set of data to illustrate what can be expected for yield increase and SCN reproduction suppression.

Since 1996, Tylka adds the Iowa State University SCN-resistant Soybean Variety Trial Program has assessed the agronomic performance and nematode control of thousands of resistant soybean varieties in experiments conducted in SCN-infested fields across Iowa. Recent economic analyses show the research program from 2011 to 2016 yielded a 91:1 to 109:1 return on investment for the soybean checkoff funds invested in the project.

“We know there are nematodes in our soils, but we don’t think it’s a problem because we don’t see them,” says April Hemmes, soybean farmer from Hampton, Iowa. “All we need to do is take the time to research the correct varieties to plant. A rotation of varieties that have been tested by Iowa State University and found to have true resistance gets that extra bushel for more profit.” 

Tylka notes, “On average in our variety trial experiments, SCN-resistant soybean varieties yielded 5 to 25 bushels per acre more than susceptible varieties. In addition to yielding more, the resistant varieties kept SCN population densities from increasing. Susceptible varieties allowed SCN populations to increase to 11,000–20,000 eggs per 100 cc of soil at harvest.”

Based on the work, Tylka recommends farmers put in some added effort for variety selection. 

“It is clear from the results that there is great variation in how well SCN-resistant varieties control SCN numbers as well as how well they yield,” he says. “It is difficult because there is no legal definition of a variety resistant to SCN and there really isn’t an industry standard. Some seed companies confirm varieties they call resistant truly allow reduced nematode reproduction, but others labeled as resistant allow as much SCN reproduction as a susceptible variety.” 

Another major point, emphasizes Tylka, is that a great majority of resistant soybean varieties will have resistance genes from the same breeding line, PI 88788. And because varieties with that source of resistance have been grown throughout the United States for more  than 25 years, he has seen widespread and convincing data that show SCN populations in fields have developed increased reproduction on varieties with PI 88788 resistance. 

“Farmers would be well served to seek out soybean varieties with a source of SCN resistance other than PI 88788, namely Peking. The number of different soybean varieties with Peking resistance is limited, but it is worth the effort to identify such varieties and grow them in rotation with varieties with PI 88788 resistance to slow the gradual loss of its effectiveness,” he says.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.