Significant flooding in many areas of the Midwest may have done more than drown newly planted crops and hinder development — it may have given soybean cyst nematode (SCN) the opportunity to move into new areas.
“Considering how much flooding occurred across the Midwest and the historical movement of soybean cyst nematodes, it's highly likely SCN moved into fields that previously may have tested negative,” says Shawn Conley, state soybean specialist at the University of Wisconsin.
“There's a valid concern, especially in states where SCN is not widespread,” says Greg Tylka, professor of plant pathology at Iowa State University. “Flooding occurred in many fields that may not have seen that amount of water in many years.”
Soybean cyst nematodes are very durable, and hitching a ride in moving floodwater can take a cyst or eggs many miles. “There's nothing in the whole flooding process that could hurt a nematode egg,” Tylka says. “SCN could easily survive a trip of 30 miles or more. Even at 300 miles, there's nothing about that venture that will hurt, especially if eggs are inside the cyst.”
Cysts are well protected against the elements, can float and can survive several weeks in water. SCN is not uncommon across flood zones, but the extent of this year's flooding, combined with the relatively new movement of SCN in some areas, may have deposited cysts, eggs or live nematodes into fields that previously tested negative.
“SCN is a relatively new pest in some northern states, and some fields this year saw flooding that hasn't occurred in decades,” Conley says. “Combine those two factors and it's a good bet that SCN advanced this year.”
IT MAY SOUND like a broken record, but testing remains a key tool in SCN management. And while SCN may have moved into a new field this year, it may be 10 years before nematodes reach levels to cause economic damage.
“It's hard to convince producers of the seriousness of SCN unless you've had it in your fields,” Tylka says. “Sample often and catch SCN early.”
It's a tough message, but one that doesn't get old. “I've been at Iowa State for over 18 years, and I still run into producers who haven't tested for SCN. They may have it and not know about it,” he says. “SCN is sort of like high blood pressure: it can be very serious if not controlled early. So the key is to catch it early.”
Nematodes need time to establish in the soil, so even testing this fall may not detect SCN. “It takes time to build up, and our soil extraction methods are not 100% effective,” Tylka says. “So a test that shows zero doesn't always mean zero.”
In fact, a statewide recent review of soil samples for SCN that are part of survey funded by soybean check-off dollars at Iowa State revealed that 20-30% of the soil samples in which zero SCN eggs were detected were actually infested with SCN. (That is, SCN females formed on soybean roots grown in the leftover survey soil samples after they had been tested for SCN eggs). “So it's imperative that producers continually test — especially in fields that you are going to grow beans in the next year,” Tylka says.
The bottom line is testing is always a good idea. “If there's significant flooding, make sure to test those fields,” says Hunt Wiley, research director at Dairyland Seed. “SCN won't show up all of a sudden, but it's a pest that does serious economic damage.”