What is Soybean Cyst Nematode?

By Dow AgroSciences.

Soybean Cyst Nematode (SCN) is a microscopic roundworm, Heterodera glycines, and is related to the animal-parisitic roundworms that infect livestock and pets.  Juvenile nematodes are the stage that actually enter the soybean root and can be either male or female. The female juvenile nematode is the form that causes plant damage, primarily due to the feeding of the female and the indirect effects of such feeding. A soybean cyst is the ‘brown stage’ or dead form of the female.

Each cyst can contain up to 500 eggs. The cyst protects the eggs from the harsh soil environment, helping them to persist for years in a dormant stage. SCN can complete up to six generations during the growing season.  Best time to look for SCN infestations is to observe white females on soybean roots. These females are easiest to spot in the field at about the time soybean plants are beginning to flower. The nematodes are easily dislodged, so the root system must be dug up very carefully with a shovel and the soil gently removed. The presence of white females will confirm a SCN infestation; however, they cannot tell you much about the level of infestation. The only way to get a reliable diagnosis of the level of infestation is through analysis of a properly collected soil sample by a  professional diagnostic laboratory. 

SCN AFFECT ON SOYBEANS 

SCN cannot reproduce without a host plant - see host plant chart below. It’s important to note that conditions that favour soybean growth also favour SCN development.  SCN effect soybean plants by the removal of plant nutrients, disruption of nutrient and water uptake in roots and retarding of the root growth. Soybean growth and yield is directly related to the numbers of nematodes feeding on the root system. Nematode damage is often not visible during the soybean growing period; however, yields are  low because fewer pods develop on the infected plants.  SCN interacts with other pathogens that are present in  SCN-infested fields. SCN infections create openings on  the root surface that can serve as entry points for other soilborne  soybean pathogens such as Pythium, Rhizoctonia,  Phytopthora, Fusarium, and Macrophomina.    

SCN DAMAGE

Visible damage and SCN infestations do not always go together. Professional diagnosis is the best way to determine if you have SCN in your fields. Symptoms of SCN infections are highly variable and can range from no visible evidence of plant injury to plant death in SCN ‘hotspots’. The symptoms commonly associated with SCN damage are similar to other crop production problems such as potassium and nitrogen deficiencies, iron deficiency chlorosis, herbicide injury, soil compaction, drought stress and other soybean diseases. In high-yield production fields (greater than 40bu/ ac) or during years when soil moisture is plentiful, visible symptoms of SCN damage are rarely seen. SCN infestations are often suspected when poor or no-longerincreasing soybean yields are observed over several years, uneven plant height in the field, a delay in canopy closure and/or early senescence.

SCN MANAGEMENT

Once SCN has become established in your field it is impossible to eliminate it, so management becomes key. It is easier to keep SCN numbers low than to try to reduce a high population. Repeated use of the same SCN resistance source will result in development of an SCN population that is adapted to that variety. Most companies market soybeans with the PI 88788 SCN resistance source. Several companies, including MycogenTM, are now offering soybean varieties with the Peking (PI 548402) resistance source. Crop rotation with non-hosts will also help reduce the risk of resistance in the SCN populations in your fields. These non-hosts help decrease the numbers of SCN and slow down its adaptation to resistant soybean varieties. Successful SCN management is an integrated process and below are several factors that should be considered when dealing with SCN:

• Grow Resistant Soybean Varieties which will help reduce the ability of SCN to develop and complete its life cycle. Resistant varieties primarily slow down SCN reproduction rates. The use of resistant varieties allows you to grow soybeans profitably now, while managing SCN numbers so that soybeans can be grown profitably in the future. Repeated use of the same SCN resistance source will result in development of an SCN population that is resistant to that variety, so rotating SCN resistance types is a good practice to incorporate in your management strategy.

• Crop Rotation produces many benefits. If you have SCN, your rotation should include non-host crops and resistant soybean varieties and should not include other SCN host crops. Non-host crops cannot be used as a food source by SCN, thus SCN numbers will not increase that season, and any eggs that do hatch will starve, thus reducing SCN egg numbers in the field.

• Cultural Practices to Improve Soybean Plant Health will help plants compensate for damage by SCN but do not decrease numbers. These practices include maintaining adequate soil fertility, breaking hardpans and controlling weeds. Un-stressed soybeans are more likely to continue to grow, flower and fill pods even with SCN pressure.

• Nematicides and Seed Treatments can help keep SCN numbers in check. Most seed treatments work only for the initial growing period and do not provide control through the majority of the soybean growth stages from flowering to harvest when yield is determined.

SOYBEAN CYST NEMATODE Solutions for a Growing World ®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 014-0158 EN

If you have any questions of concerns about Soybean Cyst Nematode and how it can affect your field, please contact Holly at hloucas@dow.com or ask a question on Twitter @HollyLoucas.