A three-year study of soybean cyst nematodes confirms Terry Niblack's suspicions. The underground pests steal yields and leave no visible clues.
The University of Missouri nematologist said, "We have been telling producers that they are losing yields, even when they can't see any symptoms. Now we have the scientific research to back that up."
The results are dramatic. Soybean cyst nematodes (SCN) can cut yields by 20 bushels per acre, or more, from a field without showing visible symptoms above ground.
"We looked at everything," Niblack said. "There was little difference in plant height or amount of leaves or stems, even the plants were infected."
The cyst nematode is a microscopic roundworm that feeds on soybean plant roots. They restrict uptake of nutrients to the plant. Although the tiny worms are invisible to the naked eye, they attach a visible, whitish cyst to the roots. The cyst is the dead body of the female, which contains a mass of eggs."
Specialists warn that you cannot always rely on a visual exam to detect cysts. A soil sample should be submitted to a nematology lab for positive identification.
"The researchers found little difference in seed composition, that is in protein, oil, fiber or total fatty acids, between susceptible and resistant varieties in fields with SCN infestations. The difference was in yield.
Weather played a bigger role in how the soybean plants look, Niblack said.
In the study both susceptible and resistant varieties were planted side by side in SCN infested fields in five locations in three states. In all, there were 2,100 plots in Missouri, Iowa and Illinois.
In Missouri, Niblack worked with Bill Wiebold, state Extension soybean specialist. Principal investigators in the other states were Greg Tylka, Iowa State University; Greg Noel, University of Illinois; and Mike Schmidt, Southern Illinois University.
The Soybean Research and Development Council, a consortium of Iowa and Illinois soybean check-off boards, funded the research.
"Many producers say they don't use resistant varieties, because they see no effect from growing soybeans on nematode infected fields," Niblack said. "The results are not noticeable until you harvest two varieties side by side. The plants may look the same, but the resistant varieties yield a lot more.
"Cyst nematodes start robbing yields at very low levels," Niblack said. "Even one SCN egg in a sample is too many."
In some test plots, where eggs were at only 200 to 400 eggs per cup of soil, which is a barely detectable level, the loss at the end of the season ranged from two to seven bushels per acre.
Niblack said the message for soybean producers is to go looking for the nematode infestations before symptoms become obvious.
Planting soybean varieties with bred-in resistance will pay off in increased yields from the very first year, Niblack said. Some producers are losing big yields year after year--and don't know it.
A 30% yield loss to cyst nematodes, which is not uncommon, is a big economic loss, she said.
A guide sheet, "Soybean Cyst Nematode: Diagnosis and Management" G4450 is available from county University Extension centers or from MU Extension Publications, 1-800-292-0969, or on the Internet at http://muextension.missouri.edu/xplor/agguides/crops/g04450.htm
The guide contains details on sampling for cyst nematodes. Information on submitting soil samples to the MU nematology lab can be obtained at local University Extension Centers.