In a new video series titled “Let’s Talk Todes,” Iowa State University Nematologist Greg Tylka and North Dakota State University Plant Pathologist Sam Markell discuss how weather impacts soybean cyst nematode reproduction.
“We have data verifying that SCN is worse in hot, dry years,” Tylka said. “It’s not just because plants are stressed from drought, but also because the nematode is reproducing much quicker, raising population densities.
“We don’t know the mechanism of it, but reproduction happens much more quickly, creating more generations in a single growing season that ultimately leads to higher egg counts during fall soil sampling,” Tylka said. “In areas impacted by drought with a traditional corn-soybean rotation, I would expect that in 2022, many of the fields that grew soybeans this year would have increased levels of SCN and increased yield loss.”
In 2017, Iowa State University published research compiled from more than 25,000 variety trial plots that showed SCN reproduction on PI 88788 had increased over the 15 years studied while yields of resistant varieties decreased. The research revealed that when soil moisture decreased and soil temperature rose, soybean cyst nematode numbers increased linearly.
Take the test
The Soybean Cyst Nematode Coalition encourages growers to test for SCN so they know their number and can start an active management strategy.
SCN soil testing recommendations can vary by state, and some state soybean checkoff organizations have free soil sampling programs. State-specific advice is available by visiting The SCNCoalition.com. Click on "recommendations" and select your state in the "coalition experts" section.
“Successful management of SCN starts by knowing your number,” says University of Missouri Plant Pathologist Kaitlyn Bissonnette. “In Missouri, I recommend growers get a SCN egg count every three years.”
“In the Midwest, surveys have shown SCN to be found in 50% to 80% of fields,” says Tylka. “If a grower doesn’t know he or she has it and isn’t actively managing it, potential yield can be lost. After the results of the soil test are known, growers can select SCN-resistant soybean varieties and determine if a seed treatment is needed, or they might alter the rotation and slot in a second year of corn to try and reduce SCN population densities even more.”
Tylka says once SCN is detected, it will always be there at some level, which is why he encourages soybean growers to find it before populations explode. “It’s always there and it’s always going to be reducing yield. It might be 3 or 4 bushels per acre or it might be 23 or 24 bushels per acre. But you won’t know until you test your soil,” he adds.
Bissonnette says a SCN soil test can also demonstrate if a grower’s management is effective. “After you have a baseline, coming back and testing soybean fields after harvest will tell you if modifications need to be made.”
Click here for a list of laboratories that process SCN soil samples.