Frequently Asked Questions. About SCN and The Coalition.
The PI 88788 SCN resistance source is used in about 95% of all SCN-resistant varieties, and it's starting to lose its effectiveness in some soybean-growing states. SCN populations are adapting to and reproducing on PI 88788. As SCN populations increase, yields decrease - and the problem is getting worse.
Nature finds a way. Just like weeds have become resistant to herbicides after years of use, using the same SCN resistance source in the vast majority of SCN-resistant soybean varieties over decades has led to SCN populations adapting to and overpowering the resistance.
The scientific definition of resistance: <10% SCN reproduction on a variety. There is no legal definition. Unfortunately, SCN' s ability to reproduce on PI 88788 at greater than 10% is common in most areas, and on the rise. As SCN reproduction increases, yield decreases.
Think of it like blood pressure. You need to know your BP before you decide how to manage it. With SCN adapting, populations with the ability to reproduce on PI 88788 at greater than 10% are common in most areas, and on the rise. In fact, 30% or higher SCN reproduction on PI 88788 isn't uncommon in many soybean-growing states. As SCN increases, field decreases. If you don't know your number you could be losing yield.
Here’s the math: If half of a cup of soil starts with 100 eggs, around half of those eggs will be female and produce 250 additional eggs each. Even with a 95 percent egg mortality rate, after three generations there would be 24,414 eggs in that same half-cup of soil. Depending on the environment, most north central states will experience three to six SCN generations in one growing season, so that number could be exponentially higher for some farmers.
That depends on where you farm, what your SCN numbers are, and what your next crop will be. For example, a grower in North Dakota will have more non-host crop options than a grower in Iowa. Talk it over with those who advise you – Extension, agronomists, seed salesmen, industry reps or crop consultants – about the best way to actively manage SCN on your farm.
Your seed salesman may know. In any case, the next time you plant soybeans (after rotating to a non-host crop), plant a different resistant variety. Not all SCN-resistant varieties are created equal.
You're not alone. The next time you plant soybeans (after rotating to a non-host crop), plant a different resistant variety. Not all varieties with the PI 88788 SCN resistance source are created equal.
Here are two common recommendations:
- Every three to five years
- Every second or third soybean crop
Check with your advisor or Extension specialist.
This can change from year to year, so check with your state soybean board. In 2017, these state soybean boards offered free SCN testing: Michigan, Nebraska, North Dakota, South Dakota and Wisconsin.
Two decades ago, the PI 88788 SCN resistance source worked very well. Two decades later, nature is finding a way around it. Just like weeds have become resistant to herbicides after years of use, using the same SCN resistance source in the vast majority of SCN-resistant soybean varieties over decades has led to SCN populations adapting to and overpowering the resistance. As SCN populations increase, yields decrease.
Any public or private entity can join us. Our goal is simple: Turn up the volume on the changing nature of SCN and encourage growers to "Know Your Number" and Take the Test. Beat the Pest.
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More than 90% of SCN resistant soybeans have the same source of SCN resistance (PI 88788), which has been used widely for more than 20 years. The PI 88788 SCN resistance source is starting to fail in some soybean-growing states. SCN populations are adapting to and reproducing on PI 88788. As SCN populations increase, yields decrease — and the problem is getting worse.