“A farmer must wear many hats” is perhaps the greatest understatement ever. You must manage tar spot, sudden death syndrome and corn rootworms. Today, you must also know herbicide modes of action and if Product X mixes well with Product Y. And then there is soybean cyst nematode — talk about complex, with resistance, female indexes and HG types.

“Hey, I don’t worry about soybean cyst nematode,” you say. “I don’t farm sandy soils.”

Not so fast. Betsy Bower, who spent years as an agronomist with Keystone Cooperative, a major Midwestern co-op, suggests you reconsider. Before the 2024 growing season, Bower collected samples from fields in western and southwestern Indiana in cooperation with BASF.

“About 65% of samples were positive for SCN,” Bower reports. “There was a higher-than-average number of sandy soils. But there were plenty of silt loam soils, too. In fact, one of the highest egg counts was a silt loam field.”

Many tests were pulled in cornstalks ahead of soybeans. “You will likely find higher numbers right after soybean harvest, but we wanted to know what farmers could expect in soybeans,” Bower says.

Who should test for SCN?

That’s more evidence that everyone should test for SCN, Bower says. Horacio Lopez-Nicora, Extension plant pathologist at Ohio State University, agrees. Lopez-Nicora is co-leader of The SCN Coalition, organized to increase awareness of SCN.

Related:What soil types are in your field?

“At least know if you have soybean cyst nematodes in your field,” he insists. “That is the first step. Even if you haven’t seen symptoms, you could lose yield to SCN.

“Know your numbers through soil sampling and testing. Then, if you have any nematodes, even one, take action. Manage fields to control numbers and limit yield losses.”

Managing SCN

Rotation is key, Lopez-Nicora says. Initially, rotate to another crop, such as corn. When you come back with soybeans, use SCN-resistant soybeans. Ideally, future years might include wheat and soybeans with different types and sources of resistance.

Bower says growers with sandy soils who have battled SCN for a long time know that the most common type of resistance, PI 88788, is not as effective today. Nematodes developed the ability to survive, with survival rates varying among different forms of PI 88788 resistance. So, some growers seek varieties with Peking resistance.

Bower notes that while earlier Peking varieties didn’t always yield up to par, newer Peking varieties from Pioneer and Brevant perform well.

Many farmers she advised also applied a seed treatment. Currently, Saltro and Ilevo are the main options. She notes that Avodigen from FMC, a bionematicide-biofungicide, produced about a 1-bushel-per-acre advantage in her area.  

“Some growers with severe problems invest in HG testing and refine their rotation of resistance,” she adds.

DEEPER DIVE: Ohio State Extension plant pathologist Horacio Lopez-Nicora suggests that farmers with serious SCN issues should consider learning about SCN types and female indexes.

When to learn more about SCN types

Testing for nematodes is inexpensive, normally around $20 per sample, with some states offering free testing. An HG type test costs about $100. HG stands for Heterodera glycines. Labs grow nematodes from your soils and determine if they reproduce on soybean breeding lines used as sources of SCN resistance.

Who should consider HG testing. If you have severe problems with SCN, sharpen your skills, occasionally wearing a plant pathologist hat, Lopez-Nicora says.

How HG type test works. There are seven indicator lines, Lopez-Nicora explains. Peking is labeled No. 1, PI 88788 No. 2, and so forth. If 10% or more of the SCN population reproduces on a line, the number of the line becomes part of the HG type.

Suppose surviving numbers for lines 1 through 7 are 15%, 60%, 0%, 0%, 5%, 0% and 5%, respectively. The SCN population would be labeled HG Type 1.2.

“The 1 signifies that the SCN population will have at least 10% reproduction on Peking lines, and the 2 means it will also have 10% or more on PI 88788 lines,” Lopez-Nicora says. “That’s a problem since those are your two sources of commercial resistance.”

What “female index” means. All is not lost if your variety is HG Type 1.2, Lopez-Nicora says. The percentage of the SCN population surviving on a line is also the “female index.” It is calculated by dividing mean number of SCN females produced on an HG indicator line by number on a susceptible line and then multiplying by 100.

How to use female index. “In this example, 15 — female index for Peking — is not far over 10, but 60 — female index for PI 88788 — is much higher,” Lopez-Nicora says. “So, you could opt for a Peking variety to manage rotation over time. However, you can’t come back with Peking every time, or you risk developing resistance.”

Bonus info. Female index is a factor in the SCN Profit Checker Calculator on The SCN Coalition website. It estimates potential yield losses. The formula assumes a female index assigned to your state. If you know your actual female index, Lopez-Nicora says your estimate will be more accurate.