The soybean cyst nematode or SCN is a consistent threat to profitable soybean production in Iowa each year. In years of adequate to excess rainfall, like 2010, the short-term effect of SCN on soybean yields may be reduction of only a few bushels per acre. But in hot, dry years, yield loss can approach 50% or more.
"No matter what is the extent of yield loss, SCN numbers can increase dramatically within a growing season if susceptible soybean varieties are grown," says Greg Tylka, Iowa State University Extension nematologist. "And high SCN numbers jeopardize long-term profitable soybean production."
Hundreds of soybean varieties that are resistant to SCN are available for Iowa growers. Resistant varieties yield well in SCN-infested fields, and they also keep SCN numbers from increasing. It's important for growers to know what soybean varieties are resistant to the nematode and what sources of resistance the varieties possess, says Tylka. He recommends rotating different sources of resistance and different SCN-resistant varieties to prevent the buildup of SCN populations with increased reproduction on resistant soybean varieties.
An added benefit of growing SCN-resistant bean varieties
To help Iowa soybean growers know their options for SCN resistance, ISU Extension annually publishes a list of SCN-resistant soybean varieties in maturity groups 0, 1, 2, and 3. The 2010 version of the publication, developed with soybean checkoff funds from the Iowa Soybean Association, has been recently released and is available at ISU Extension Online Store as publication PM 1649 at www.extension.iastate.edu/store. The publication is also available on the Production Research section of ISA's website at www.iasoybeans.com/productionresearch/productiontech.html. Printed copies of the publication will be available in late 2010 or early 2011.
An added benefit to growing SCN-resistant soybean varieties may be less severe occurrences of soybean sudden death syndrome, a soil-borne fungal disease that devastated soybean fields in parts of Iowa in 2010, says Tylka.
There is a connection bewteen SDS and SCN infestations
He adds, "In years like this past season, when weather and other conditions are right for SDS to develop, soybean fields that also have SCN will show symptoms of SDS earlier in the growing season, and the SDS symptoms develop to higher levels than in fields not infested with SCN. Earlier appearance of SDS symptoms and increased symptom levels lead to greater yield losses. Growing SCN-resistant soybean varieties won't protect fields from SDS, but it may lessen the aggravating effect of SCN on SDS."
The 813 SCN-resistant varieties that are listed in the updated ISU publication are the most ever, but almost all of the SCN-resistant varieties in the publication have the same source of resistance, notes Tylka. That source comes from a breeding line called PI88788. Only 15 of the 813 varieties in the publication have a source of resistance that is not PI88788.
"I would also point out that 21 SCN-resistant soybean varieties in the list were developed by ISU scientists with soybean checkoff funding from the ISA," he says. Two of the varieties, "IAR2101 SCN" and "IAR3001 Phyto SCN," have sources of SCN resistance that have not been used in any soybean varieties previously included in the list.