BLOOMINGTON, Ill. — Herbicide-resistance across weed species and geography has been in the news for years, and now a similar development is happening underground.
Soybean cyst nematodes have been evolving into resistance to the PI 88788 soybean, a germplasm used in 95 percent of the seed market share that helped control SCN.
“It’s nothing new. It just appears to be getting worse. It just multiplied over the years,” said Stephanie Porter, Burris Hybrids sales agronomist.
“A smaller percentage source of soybean resistance against SCN comes from Peking, PI 437654, or combinations.”
SCN’s resistance was first noted about eight years ago by Terry Niblack, then-University of Illinois Extension nematologist and now chair at Ohio State University’s Department of Plant Pathology.
Diagnosing SCN is difficult as they can be located within patches across a field.
“I was actually visibly able to see it in the field for the first time this year. You are able to see more symptoms of SCN during drought years just because they have less roots. We’ve had several years that we’ve had a lot of rain and that can mask it,” Porter said
“But you also have to be careful because there are so many other things going on out there — root rot, compaction, pH levels and soil nutrient deficiency. Basically, you just have to rule it out.”
Porter said in cases of high populations, SCN cysts might be visible on roots, and there could be poor nodulation, uneven soybean growth, stunted plants or a low number of pods or soybeans per pod.
To rule out SCN, Porter sends a soil sample to the U of I Plant Clinic and another to a soil lab, and she also looks at the roots to make sure they’re not rotted or stunted by compaction.
Another option is the Hetorodera glycines test. Niblack was one of the first to use the HG test on populations within a field. The test determines if a there is a population of nematodes that are able to overcome PI 88788.
Iowa State University’s recent research found that an HG type test is most meaningful if a soil sample of 100 or more cores is collected throughout a field.
“It’s a little bit more an expensive soil test. The U of I Plant Clinic does it as do commercial soil laboratories. It also takes a long time to do it,” Porter said.
The procedure includes a 30-day greenhouse test to determine the SCN female index, the average number of SCN females produced on the HG type indicator line relative to the number produced on a standard, susceptible soybean cultivar.
With limited resistance provided by germplasm options, Porter said there is a movement toward seed treatments.
“It’s not going to be the ultimate savior, but that’s one thing you can do for early season control. Various companies have come out with different seed treatments. For example, we chose to go with ILeVO as an option for sudden death syndrome and SCN,” Porter said.
“That’s the one thing we can do now, but ultimately we’re waiting for more discoveries to happen. They have just discovered the genes that underline SCN resistance and we’re just kind of waiting for more things to happen in that arena and, hopefully with more funding and that kind of thing, we’ll be on the right path.”
Crop rotation and tillage can help reduce SCN populations, but won’t eliminate it.
“A lot of people have been saying maybe they can make more money with soybeans. That’s normal in Missouri, but there are so many problems that could come, one of them being your SCN population is just going to skyrocket,” Porter said.
“SCN cysts can remain in the soil for several years, and each cyst can contain more than 100 eggs. When they hatch, the juveniles will migrate to the plant root, set up feeding sites and steal nutrients, which can result in yield loss. SCN have also been deemed the ‘gateway for disease’ such as sudden death syndrome.”