Research Highlights

Soybean Growers Can Manage for SCN, Maintaining Higher Yields

By Sarah Hill

Here’s a riddle: name the pest that persists in the soil forever, cannot be eliminated, shows no symptoms on the plants, can reduce soybean yields, and lowers soybean growers’ profitability? You guessed it — soybean cyst nematode. 

Microscopic nematodes are more commonly known as roundworms, and according to Erik Smith, Area Field Crop Specialist, Cornell Cooperative Extension, they’re everywhere. 

“In the scientific community, roundworms are considered the most abundant organism on the planet,” he says. “They’re in the soil, found in vertebrates, plants, animals, and free living in the environment.”

However, Smith clarifies that nematodes can be host-specific. For example, plant parasitic nematodes only feed on plants. SCN can infect agricultural crops including soybeans and clovers. 

This pervasive organism can also occur in conjunction with several fungal pathogens, including white mold. When present together, SCN and white mold can reduce yields even further than only one of the pathogens by itself.

An Invisible Problem

“The most concerning quality of SCN is that the grower doesn’t know they have it just by looking at the plants,” says Smith. “It’s scary, because the grower may think everything is fine, but they’re actually losing money.” 

Affected plants may be stunted in appearance, but it’s subtle, according to Smith, and may be attributed to other issues, such as drought. 

SCN establishes itself by infecting plant roots with free-living juvenile roundworms. Female nematodes make their home in the roots, maturing there and filling their body with eggs. The eggs solidify, becoming a cyst that can persist for years — even after soybeans have been harvested. The entire time, the roundworms are sapping the soybean roots of nutrients, preventing the crop from taking up all the nutrients that are available and making the plants more susceptible to other pathogens.

“A grower might see a lush, green plant, but it’s just not thriving as it should be,” Smith says.

Widespread Problem

So far, Smith says that SCN is widespread across New York, but most fields seem to only have low populations of SCN, with only two fields showing high populations. A few counties have moderate levels.

“SCN populations are measured by the number of eggs in a cup of soil,” he says. “Less than 500 eggs per cup is considered low. Five hundred to 10,000 eggs is moderate, and more than 10,000 eggs is considered high.”

Smith recommends conducting soil testing in high-risk areas of crop fields, including the entry, headlands, areas prone to high traffic, sections that flood or remain wet, any consistently low-yielding areas, or low spots.

“SCN is very common in areas of infested fields near trees or in the shade,” he notes. “If you know you have the pest, keep tabs on the population levels each year, so you can better manage for it.”

Soil samples should be kept moist and shipped immediately after sampling to a SCN analysis lab for the best results.

“Make sure you’re testing the soil year after year and scouting your fields to be aware of any SCN population in the soil,” he says. 

Management Strategies

Crop rotation is one of the management strategies for dealing with SCN. Seed treatments are available for fields with especially high SCN populations. Another option is to select soybean varieties that are resistant to SCN, but that may not be a choice for much longer, according to Smith. 

“In recent years, SCN has begun to overcome that plant resistance,” he says. “If you’re a soybean grower with SCN, there are type tests for SCN that can help determine what type of nematode is present, so you’ll know if those resistant soybean varieties will be effective in your fields.”

Type testing the SCN is helpful in managing the pest, but Smith says that populations need to be fairly high for results to be conclusive. Throughout the Midwest, SCN populations have overcome commonly used resistance traits in many soybean varieties that were once SCN resistant. 

“It’s on our radar and we’re monitoring fields every year,” Smith says. “However, PI 88788 is starting to fail throughout the Midwest. If resistant SCN populations are present, growers should definitely explore SCN-resistant seed treatments, but that can’t be the only tactic they employ.”

Another concern for growers is the fact that crops like pinto beans, navy beans, kidney beans and black beans are all susceptible to SCN, in addition to soybeans. Although rotating out soybeans for a year can reduce SCN populations by as much as 50%, growers have to be careful to select non-host crops for rotation. 

Growers have a difficult challenge to prevent an SCN infestation if the pest is in their county or state, but one suggestion Smith offers to stave off nematodes is cleaning equipment between fields — which is especially important for custom operators. 

Soybean growers should have a management plan in place to protect their yields and profitability from damage by SCN that includes a variety of strategies and soil testing.

Published: Nov 13, 2023