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The Best Soybean Cyst Nematode Resistance
Just when you think you have a crop pest whipped, the little buggers sneak back. That’s true of the soybean cyst nematode (SCN). It has been fought against with resistant soybean varieties, seed treatments, and crop rotation for many years with success. Still, it keeps coming back.
The problem comes in fully understanding two things, says George Bird, a Michigan State University entomologist. These two things are the source of varietal resistance and the type of SCN you have in your soil.
Source of resistance
There are really just three SCN-resistant genetic sources in all soybean lines, Bird explains. They are designated by the genetic lines PI 548402, PI 88788, and PI 437654. The first two are dominant lines used to impart resistance. Seed companies will often label their varieties as resistant or moderately resistant to SCN, but Bird says you need to ask for the exact line of resistance – one of those three numbers.
“They should know it, and they should tell you,” he says.
Those genetic lines show different levels of resistance to the various types of SCN. The dominant ones are Type 0, Type 1, Type 2, and Type 4. Types 0 and 2 represent about 95% of the problem, Bird says, and you can only know which type is in your fields by a soil analysis done at a qualified lab.
Once you know your resistant line of seed and your type of SCN, then you can plot the two against each other. Bird has done that in the table that he developed.
Is it worth the trouble of knowing your SCN type and the resistance source in your seed? Absolutely, says Bird. It can easily be worth up to 10 bushels per acre.
“In one of our 2015 yield trials, we had an SCN susceptible variety in which we counted 29,840 SCN eggs in a 100-cc soil sample,” he says. “Where we planted a similar variety with PI88788 source resistance, the egg count was 536. The yield went from 57 bushels an acre up to 64 bushels with resistance. Sometimes it adds much more than that.”
George Bird, Michigan State University entomologist, lists some of the problems and solutions for battling soybean cyst nematode (SCN).
- SCN eggs can remain alive in the soil for up to 10 years, even without a host to feed on.
- Crop rotation helps, but it won’t eliminate SCN because of the 10-year survival in the soil.
- While SCN is often very visible to the naked eye with stunted plants and yellow foliage, sometimes it isn’t. “We’ve seen 10-bushel-an-acre yield hits or more with no visible symptoms,” Bird says.
- Biological seed treatments (such as Poncho/Votivo and Clariva) and chemical controls (such as Avicta) can be effective at preventing SCN from colonizing the plant and poisoning it. Bird says they should be used in addition to planting the appropriate line of resistance.