What are Soybean Cyst Nematodes, and How are They so Damaging to Soybeans?

Soybean cyst nematodes, commonly known as SCN, are one of the most destructive pathogens to soybeans in the United States. To learn more about these destructive pests, we looked through multiple SCN resources and reached out to soybean cyst nematode expert Dr. Greg Tylka for more information. to see all of the questions we asked, and the answers from Dr. Tylka, click on the link below!

According to Dr. Tylka; “SCN is estimated to cause $1.2 to $1.5 billion in damage annually in the US and Canada. On a field level, SCN has reduced soybean yields by >20 bushels per acre in field experiments in Iowa.” So what exactly are these yield damaging pests?

Soybean cyst nematodes, as the name implies,  is a type of nematode, which is an unsegmented roundworm. It has several lifecycle stages, but the most recognizable is the final stage of the female soybean cyst nematode where a portion of the female begins to protrude from the root, and becomes visible to the naked eye (if you pull up the plant).  While Soybeans are the most common host, SCN will affect other host plant species with varying degrees of success. Once attached to a host, the nematode will siphon nutrients from the roots of the plant to feed itself. Too many nematodes and the plant may become nutrient-deficient, leading to a smaller yield. If other environmental factors cause too much additional stress on top of the nematode feeding, the infestation can also cause a portion of the plants to wilt and die.

According to the University of Minnesota Extension, soybean cyst nematode’s have a series of lifecycle stages going from egg, to juvenile, to adult. SCN goes through four separate iterations of the juvenile stage before becoming a full adult. After hatching from its egg, a juvenile SCN will hunt for actively growing roots, and begin its infection by penetrating into a host plant’s roots. Once there, it will begin feeding in the vascular tissue of the root. After three molts, SCN will enter its adult phase. Females will soon begin to protrude outside of the root, and males will become a more motile worm-like creature. At this stage, the male will stop eating, and begin looking for female SCN to begin the breeding process.

Once fertilized, the female will deposit a small number of her eggs soon after, and hold onto the rest. The clutch of eggs laid shortly after fertilization will develop enough to infest the roots again during the same year, increasing the number of SCN in the roots and soil. As the female ages and eventually dies, its body forms what is referred to as a cyst, which is used to protect the remaining eggs within the female from damage, allowing them to survive the winter and other dangers. Eggs within the cyst can last for several years before hatching, allowing re-infestation of a field to occur even after a crop rotation.

The main symptom for heavy SCN infestations according to Dr. Davis and Dr. Tylka in their article, Soybean Cyst Nematode Disease, are large portions of soybean fields “with plants that are severely stunted and yellow or dead”. The problem, however, is that this is the only real visible symptom above ground, making SCN more difficult to detect. SCN’s main symptom is also commonly attributed to other issues, which can cause the infestation to expand rapidly as the actual root cause is not dealt with. This is why sampling and discovering the infestation early is important.

While some states have all or nearly all counties infested, it is still possible to go several years without realizing there is an SCN infestation. The above-ground symptoms are often barely noticeable, or easily attributed to other yield-affecting factors. As such, proper scouting for an infestation is important so that you can begin management practices before SCN numbers grow out of control.

We asked Dr. Tylka what he and his team suggested for SCN sampling and testing. Dr. Tylka let us know the following;

“The most effective way to check for SCN fields is through soil testing. Soil samples for SCN testing can be collected anytime throughout the year except when the soil is: 1) frozen, 2) snow-covered, or 3) muddy.”

“The best approach is to collect soil samples for SCN testing in the fall, after harvest but before the ground freezes, and to soil sample fields that will have soybeans grown there in the next growing season. Proper soil sampling involves collecting 10-20 8-inch-deep soil cores with a 1-inch-diameter soil sampling probe in a zig-zag pattern from no more than 20 acres per sample.”

“Nonhost crops, such as corn should be grown in annual rotation with soybeans in SCN-infested fields. SCN numbers will decline in years when nonhost crops are grown.” Dr. Greg Tylka

As noted in the Iowa State Extension’s article on Soybean Cyst Nematodes, without a host, SCN cannot reproduce. A highly effective strategy to help lower SCN numbers from one year to the next is to rotate in non-host crops. Without a food source, any SCN that hatch will have nothing to eat, and die. While a good crop rotation will help keep numbers in check, due to the longevity of the cysts and how long the eggs remain viable, it is nearly impossible to fully wipe out a SCN infestation while rotating crops. If you intend to try this strategy, verify your choice of crop is not a suitable host for SCN before beginning. The Purdue Extension provides a chart that lists many of the common host plants for SCN, and how effective a potential host species is. The chart also lists several non-host plants that SCN struggles to affect and would make great rotation crops for reducing SCN numbers.

A common defense against different plant pathogens, resistant varieties of the desired crop tend to be an effective method of control. The same goes for SCN. The two most common resistant varieties are PI 88788 and Peking. However, as Dr. Tylka informed us,  SCN can adapt to a resistant variety if used multiple seasons in a row, and with how effective the Peking variety is currently, it can quickly lose that efficiency.  This is why rotating the resistant varieties helps to maintain their effectiveness for longer periods. In addition, this strategy is further enhanced by rotating non-host crops to starve out some of the nematodes that manage to develop a way around the plant resistances. 

“Nematode-protectant seed treatments can be applied to soybean seeds before planting, and these seed treatments may provide some yield protection (i.e. yield increases of 2 to 4 bu/ac).”- Dr. Greg Tylka

Most forms of Nematicides, or pesticides which are toxic to nematodes, are no longer readily available. (Purdue Extension Soybean Cyst Nematode). Instead, nematode-protectant seed treatments have become an option that provides a small amount of additional yield protection. These seed treatments are designed for early season protection from SCN, according to this NC State Extension article that explores several soybean seed treatment options for a variety of different situations. While helpful, seed treatment alone will not slow down heavy SCN infestations on its own.

Holly Andres and Zane Grabau suggest in their article on the University of Florida’s IFAS Extension that carefully sanitizing soil moving equipment can be beneficial in managing SCN. Moving soil from one field infected with SCN to a new field can start the infestation in the new field, even if it is only a small amount of soil. Making sure to clean equipment before moving to a new field can help slow SCN’s spread into neighboring fields.

University of Florida IFAS Extension; Soybean Cyst Nematode, Heterodera glycines (Ichinohe, 1952) (Chromadorea: Rhabdita: Heteroderidae)

Some types of weeds are host plants for soybean cyst nematodes. As such, making sure to keep weeds under control will increase the effectiveness of rotating to a non-host crop such as corn. Too many weeds may allow SCN to continue reproducing regardless of the main crop.

Additionally, some cover crops are hosts for SCN, which can increase infestation levels. In fields where you are dealing with SCN issues, make sure to select mostly resistant cover crops or non-hosts.

Michigan State University Extension; Integrated Management Strategies for Improved Soybean Cyst Nematode Control

We have crop insurance products designed to help protect your yields tailored specifically to your operation. Want to see what options are available to your farm? Contact us and one of our agents will work with you and take a look at your farm to help build the best risk management strategy for you.

Teams across the United States continue to investigate soybean cyst nematode infestations to find additional management options. Several potential ideas have been investigated, with a few new tools potentially on the horizon for SCN management.

With more resistant varieties, there are more options for rotating resistant soybeans to try to keep ahead of SCN. A few different varieties are in the works, including a PI 88788 resistance variety further reinforced with Bt SCN resistance. Additionally, some researchers from the University of Missouri believe they have discovered an entirely new SCN resistance. While the university article did not provide a ton of information on this resistance, their research may provide another resistant soybean variety to add to producer toolkits.

“BASF is developing SCN-resistant soybean varieties with “PI 88788” resistance that is fortified or supplemented with Bt SCN resistance. The varieties will be called “Nemasphere.”  “Bt” stands for Bacillus thuringiensis. This technology was used many years ago for resistance to insects in corn. “Nemasphere” reportedly will first become available in 2028 for a limited number of acres and widely available in 2029.”
– Dr. Greg Tylka

Dr. Tylka also provided us with a link to read more about the research, which has been provided below.

Along with resistant varieties, there have been some investigations into utilizing different microbes to combat SCN. Often called microorganisms, the most common types are bacteria, viruses, and fungi. – In Brief: What are Microbes?, National Library of Medicine. Glen Hartman and Michelle Pawlowski investigated fungi in particular to see their effect on SCN while working with the Agricultural Research Service. Their study in 2020 found that arbuscular mycorrhizal fungi in particular seem to affect SCN numbers. However, as the exact relationship between the fungus and SCN is not fully understood, they determined more research was required to discover how useful this may be.

Aside from fungi, there have been some interesting developments with bacterial defenses. a protein known as Cry14 that is produced from Bacillus thuringiensis, a soil-dwelling bacterium, has been discovered by BASF, a research company in Michigan. The protein effectively pokes holes in the gut of SCN, leading to the parasite essentially starving to death. BASF intends to utilize this trait in their upcoming Nemasphere product by creating a resistant soybean variety that incorporates the protein into the plant, causing the nematodes to die while they try to feed. According to the Progressive Farmer article that reported on this, BASF is hoping to have the product available to select growers in 2028, with a full launch in 2029.

How nematode egg hatching works has been the subject of several research projects including this one from ScienceDirect that goes over hatching factors for a large number of different nematodes. With SCN, scientists have been trying to figure out how to induce them to hatch in unfavorable conditions for the last four decades according to Dr. Tylka. Unfortunately, no one has been able to find an effective way to trick the SCN eggs as of yet.

Soybean cyst nematode infestations are not going away any time soon. However, as Dr. Tylka mentioned, SCN is a chronic health problem for soybeans and not the end of the world. By using proper techniques you can successfully manage SCN in your fields, and with continued research, new management tools may become available to deal with these destructive pests.

Dr. Greg Tylka is a Morrill professor in the Department of Plant Pathology and Microbiology at Iowa State University. He additionally has several responsibilities with the Iowa State University Extension for plant-parasitic nematodes. Dr. Tylka has been studying Soybean Cyst Nematodes for a long time, starting in 1986. We want to thank Dr. Tylka for taking the time to answer our questions for this article, and for all the hard work he and his team have done investigating SCN over the years!

This map from the SCN Coalition site shows the currently known distribution of soybean cyst nematodes in the US and Canada as of early 2025. Additional information is provided on their page!