percentage map
TOO HIGH: A soybean cyst nematode-resistant variety should allow less than 10% reproduction. Today, these states show much higher rates than that on PI 88788 — including 88% in Illinois.

Take the test, beat the pest (again)

Like the disease it fights, the SCN Coalition is back with a vengeance.

In some circles of the pest fighting world, it’s déjà vu.

You may remember the fight — and the phrases — surrounding soybean cyst nematode management in the ’90s: “Take the test. Beat the pest.” After a 20-year hiatus, the SCN Coalition that founded that fight is back, but with a new mission.

This time around, SCN has adapted and reproduced on SCN-resistant soybean varieties, reducing yields along the way.

“SCN is still the No. 1 yield-reducing pest,” says Greg Tylka, Iowa State University nematologist and a veteran of the first SCN Coalition. “We’ve become a victim of our own success.”

Tylka says managing SCN has become more complicated than planting a resistant variety and assuming the problem is solved. Twenty years ago, the advice was to test for SCN, and if the results came back positive, plant an SCN-resistant variety.

The kicker? Today, more than 95% of all SCN-resistant soybean varieties contain the same source of resistance from the PI 88788 breeding line. Tylka says it’s natural selection in action.

“The nematodes are adapting,” he adds.

A resistant soybean variety should allow less than 10% reproduction versus a susceptible variety. In other words, a resistant variety should stop 90% of the SCN in a field from reproducing. Currently, researchers are discovering that on some farms, one out of every two nematodes can reproduce on a variety with PI 88788 resistance (that’s 50% reproduction).

And as SCN reproduction increases, yield decrease — often without visible symptoms.

“One of the problems is that SCN can cause yield loss without the plants and the crops looking sick,” Tylka says.

Why know your numbers?
The SCN Coalition is back primarily to sound the alarm over “increasingly aggressive SCN populations,” and to encourage farmers to actively manage SCN — which starts by testing fields.

“You’ll need those numbers to understand the severity of the problem,” Tylka says. “The higher your numbers, the greater your chances of yield loss, and the higher that yield loss will likely be.”

Tylka and the coalition recommend a four-step plan to manage SCN:

1. Test your fields to know your numbers.
2. Rotate resistant varieties.
3. Rotate to non-host crops.
4. Consider a seed treatment nematicide.

The SCN Coalition is a public-private partnership that relaunched this winter at Commodity Classic. Made up of more than 40 university researchers, Extension specialists and ag industry representatives, the coalition still urges farmers to “take the test and beat the pest.” The new wrinkle this time, thanks to PI 88788 resistance: Farmers need to “know your number” and actively manage SCN.

The new SCN Coalition was organized with soybean checkoff financial support from the North Central Soybean Research Program and supplemented with additional support from the United Soybean Board and private partners. The coalition brings together all branches of the soybean industry, including academia, seed companies, seed-treatment suppliers, agronomists, the soybean checkoff and media — including Prairie Farmer’s sister publication, Corn+Soybean Digest.

For more information, check out the SCN Coalition online resource center.

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