Why Soybean Cyst Nematodes are So Darn Difficult to Eliminate
If you’re a soybean producer, you know how Soybean Cyst Nematodes (SCN) can damage your crops and lower your yields. But, how much do you really know about these pests?
You may think that a Soybean Cyst Nematode is a bug—but according to Dr. Greg Tylka, Nematologist at Iowa State University and the Director of the Iowa Soybean Research Center—it’s actually a microscopic worm!
“The worm is about 100th of an inch long, and it’s confusing to people, perhaps also because it goes into the root and attaches to the vascular tissue of the soybean root, but then it swells up. The adult female eventually gets so big that she pops out of the root, and you can see her as a little white dot on the surface of the root. In fact, that’s one way we advise that farmers and agronomists to check fields for SCN. Wait till five or six weeks after planting, and then, pretty much, through to August, maybe mid-August, dig roots and look for those little white females. Even though the nematode is a microscopic worm, you can see the swollen adult females with your naked eye. The size of a period at the end of a printed sentence. The period at the end, that’s about as big, but it’ll be white-colored and about that size, and you can see them with your naked eye.”
He says the reproduction cycle of the nematode can create challenges because they aren’t monogamous.
“There are, like humans, males and females that have to mate for offspring to be produced. The female produces all the offspring in the form of eggs. But the interesting and problematic part is a male will mate with several different females, and a female will be mated by several different males. If a female makes a total of 250 eggs, they might have 200 different genetic types because of the inner mating that occurs, so they’re not clonal. Clonal would mean that all the eggs are just like the mother’s genetics. They are a mix of the genetics of all the different males that mated with the female to produce those eggs, and that genetic diversity allows the nematode to adapt. That’s why we’ve seen the nematode adapt to and overcome the common pi 887, 88 resistance, because of that genetic diversity.”
That also means the nematode can develop a resistance to certain pesticides, which is why it’s far more difficult to eliminate them.
“88788 resistance took about 20 years to start to fall apart, and here we are 30 years into it, so it’s falling apart in that there’s lots of nematode reproduction. Peking, we don’t believe is going to be as durable, and it’s kind of counter-intuitive, but it’s not going to be as durable because it’s more effective. So, 88788 always allowed a little bit of reproduction, and so the nematode population in a field over decades always had a vulnerable part of its population. Peking is so effective that the tiny percentage that overcomes Peking is truly able to reproduce. And over time, it’s going to build up quicker than the slow curve that we saw for 88788.”
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