Marisol Quintanilla, a nematologist at Michigan State University, visited northwest Indiana on Aug. 21 to share a secret weapon against soybean cyst nematodes (SCN).
SCN is microscopic, sand-grain sized round worms that attach themselves to the roots of soybeans.
"When infected with SCN, the plant is not working for you. It's working for the nematode," Quintanilla told a group of farmers during the Pinney Purdue field day in Wanatah. "The nematode becomes obese, it becomes like a big round ball, and the female body becomes a casing for 100-250 eggs that are inside of her."
One of the devastating characteristics of SCN is that it has a long lifespan, even without a host. Quintanilla said if a farmer stopped planting in an affected field even for 20 years, that next planting would wake up the resident SCN and the soybeans would get just as damaged as 20 years before.
"We can't get rid of them, but we can manage them," she said. The best way to do this is through crop rotation. And Quintanilla has found that one crop rises above them all in cutting down on SCN.
"Wheat has superpowers," she said. "Wheat reduces nematodes better than using corn or no crops. In fact, it reduces them up to 30% more than using no crops at all."
The reason for this is still unclear.
However, Quintanilla led studies showing that SCN rates were higher in fields rotating corn and soybeans than those rotating soybeans and wheat.
She also said it is important to rotate the soybean brand in order to elongate effective resistance against the pest.
"We have been planting the same control for cyst nematodes. If you plant the same soybean type, cyst nematodes adapt. We are losing resistance," she said.
Another way to increase resistance against SCN is to rotate the resistance used, she said.
"This is hard, because there are currently only two: Peking and PI 88788," she said.
After a four-year trial, Quintanilla found that the most effective planting cycle was to use PI 88788 for two years, then rotate Peking in for one year.
Another resistance method is to apply certain manures, which create a hostile environment for SCN. The most effective manures Quintanilla's study found were poultry and swine manure. However, she said this form of resistance is much less plausible because, in order to be 100% effective, the soil composition would have to be 5% poultry manure.
"That's not really possible," she said.
However, applying poultry manure does add another layer of protection against SCN. Also, clay and heavier soils are less conducive to SCN habitation.
Finally, Quintanilla said it is important to know what type of SCN is in the field, because this will affect what type of resistance is most effective.
"It is too much to ask seed treatments to do all the work in biocontrol," she said.
It is imperative to employ and rotate various methods of resistance to deplete the SCN population in soybean fields.