Soybean Cyst Nematode (SCN) is the most damaging pest for soybeans in the U.S. and around the world. Beating Soybean Cyst Nematode requires a proactive strategy because the pest is nearly impossible to eradicate once it’s in a field. Since it’s nearly impossible to eradicate once it’s in a field, the most effective strategy is a comprehensive Integrated Pest Management (IPM) program. An IPM approach combines multiple tactics—from cultural practices to genetic resistance—to keep nematode populations at manageable levels and protect yields.
The SCN Life Cycle: Know Your Enemy
To beating Soybean Cyst Nematode, you must first understand its life cycle. The nematode is a microscopic roundworm that can complete up to six generations in a single growing season. It starts as a juvenile worm that hatches from an egg inside a protective cyst (the body of a dead female). The juvenile penetrates a soybean root, where it feeds and develops. The male leaves the root, but the female becomes sedentary, swelling into a lemon shape that is visible on the roots. When she dies, her body becomes a cyst that protects hundreds of eggs for years, even in the absence of a host crop. This ability to survive for years is what makes SCN so difficult to manage.
Integrated Pest Management (IPM) That Works
A successful IPM program for SCN relies on three pillars: testing and monitoring, crop rotation, and resistant varieties.
- Test, Don’t Guess: The first and most critical step is to know your “numbers”—the SCN egg count in your soil. Since SCN can cause significant yield loss with no visible above-ground symptoms, regular soil sampling is essential. Collect soil samples in the fall after harvest when nematode populations are at their highest. A soil test will provide a baseline egg count and help you determine the severity of the infestation, guiding your management decisions for the next season.
- Crop Rotation: SCN cannot reproduce without a host plant. Rotating soybeans with non-host crops is a highly effective way to reduce nematode populations. A crop rotation of soybeans with non-host crops like corn, wheat, or grain sorghum can reduce the SCN population by 50% in a single year. In fields with very high egg counts (over 10,000 eggs/100cc of soil), a non-host crop for one or more years is often recommended to bring populations down to a manageable level.
- Use Resistant Varieties Wisely: Planting SCN-resistant soybean varieties is the most widely used and effective control method. However, SCN populations can adapt and overcome resistance. To prevent this, it’s crucial to rotate sources of resistance. Over 95% of SCN-resistant varieties use the PI 88788 source of resistance. Continuous use of this same genetic source has led to resistance breakdown in many fields. To combat this, farmers should rotate to varieties with different sources of resistance, such as Peking, to slow down the development of SCN populations that can reproduce on resistant varieties.
Additional Management Tactics
Beyond the core three pillars, other cultural practices can help keep SCN in check:
- Sanitation: SCN is primarily spread through the movement of infested soil on farm equipment, vehicles, or even boots. To prevent its spread, clean all machinery thoroughly before moving from an infested field to a clean one.
- Weed Control: Certain weeds can act as hosts for SCN. Maintaining a robust weed control program is an important step in an IPM strategy to prevent SCN from reproducing on alternative hosts.
- Soil Health: Maintaining good soil fertility and managing other plant stresses (like drought or nutrient deficiencies) can increase a soybean plant’s tolerance to SCN, reducing yield loss.
