Why PI 88788 Soybean Resistance Is Losing Ground Against SCN

For decades, PI 88788 has been the workhorse source of soybean cyst nematode resistance in North American soybean varieties. That long run of success has also created a predictable problem: repeated use gives SCN populations more opportunities to reproduce on—and gradually adapt to—the same resistance source.

A new Iowa analysis puts numbers behind what many farmers and crop advisers have suspected. Researchers examined SCN performance in resistant soybean variety trials through 2023 and found that the nematode’s ability to reproduce on PI 88788-derived resistance increased by about 2% per year from 2001 to 2023. If the trend continues, the researchers project that PI 88788 varieties may provide only about 40% control by the end of the decade.

What this means in the field

“Resistant” does not mean immune. A PI 88788 variety may still yield better than a susceptible variety, but the protection can weaken when the field’s SCN population has adapted. That can allow egg numbers to build even when aboveground symptoms are subtle or absent.

The study estimated that, without changes in management, average losses could approach 9 bushels per acre—about 12% of yield potential. The exact loss on any farm will depend on starting egg counts, weather, soil conditions, variety performance and the local SCN population. The practical message is not to abandon PI 88788 everywhere. It is to stop treating the resistance label as a complete management plan.

Four actions for soybean growers

1. Test SCN-infested fields regularly. Sample after harvest or before planting and compare egg counts over time. A single result tells you whether SCN is present; repeated results tell you whether your program is driving the population down or allowing it to increase.
2. Ask which resistance source is in each variety. Variety names change quickly, and two high-yielding “SCN-resistant” products may rely on the same PI 88788 genetics. Work with your seed supplier to identify Peking-derived options or other resistance sources that fit your maturity group and agronomic needs.
3. Rotate resistance sources, not just brand names. Switching brands while planting PI 88788 again may apply nearly the same selection pressure. Where suitable varieties are available, alternate PI 88788 and Peking resistance rather than relying continuously on one source.
4. Use nonhost crops and other tools as a system. Corn and other nonhost crops can reduce SCN reproduction, but one rotation year will not erase a high population. Seed treatments may protect early roots or reduce reproduction, yet performance varies by product, field and season. Neither replaces host resistance and sampling.

Do not create the next resistance problem

The Iowa work did not find the same long-term overall increase in reproduction on Peking resistance. However, elevated reproduction on Peking occurred more often in recent years. That is an early warning: moving every acre from PI 88788 to Peking could simply repeat the same selection cycle.

A better strategy is diversity. Match the variety to the field, rotate effective resistance sources, include nonhosts, and measure whether egg counts respond. When comparing varieties in an SCN field, look beyond yield alone. Ask for resistance source, local trial performance and—when available—information on the field population’s ability to reproduce on different resistance sources.

A simple decision rule

If SCN egg counts rise after growing a resistant soybean, investigate before using the same resistance source again. Confirm that the sample timing and location were comparable, review the variety’s genetics, and discuss alternate resistance or rotation options with your agronomist or Extension specialist.

The most expensive SCN problem is often the one that remains invisible. Healthy-looking plants can still support reproduction. Soil testing turns resistance from a label into a measurable management tool.

Source

“Soybean Cyst Nematode Virulence to PI 88788 Soybean Resistance in Iowa: Selection Marches Steadily On,” Plant Health Progress, published July 27, 2026. Read the paper via DOI.

Wise Farmer question: Do you know whether the SCN-resistant soybean varieties on your farm use PI 88788, Peking or another source? Share what information is easiest—or hardest—to get from your seed guide.