Soybean Cyst Nematode
June 18, 2008
By Berlin D. Nelson and Rubella S. Goswami,
Plant Pathologists, Dept. Plant Pathology, NDSU, Fargo
The soybean cyst nematode (SCN), Heterodera glycines, is the most economically important pathogen of soybeans in the United States. The nematode is known to attack other plants, but most are not important crop plants with the exception of dry beans. Dry beans have been known to be a host for over 80 years, but there has been very limited research on the effect of the soybean cyst nematode on dry bean production. Most large dry bean production areas in the United States are not located in the main soybean production areas where SCN is common, thus, there has been limited concern about the potential effects of SCN on dry beans. SCN was discovered in the Red River Valley of North Dakota and Minnesota between 2003 and 2004. All the evidence indicates that SCN will continue to move north and west into dry bean production areas.
Because North Dakota and northern Minnesota is a region with a large dry bean production, we are concerned about the potential damage SCN may cause. A serious problem in soybean production has been that you can have yield loss without obvious above ground symptoms. This makes it difficult to diagnose the problem. A similar situation may occur in dry beans. SCN can be seen with the naked eye on the roots of dry beans. The white females are swollen and protrude from the root, but you have to carefully examine the roots to find them when populations are low.
Research conducted at NDSU has shown that SCN can reproduce on dry bean cultivars grown in this region. Kidney beans are as susceptible as soybeans, whereas pinto and navy beans are a little less susceptible and black beans appear to be the least susceptible. In 2007 we demonstrated that SCN reduced the growth of pinto beans in the field (as reported in the Northarvest Bean Grower Volume 14, Issue 2). There had never been evidence reported previously of a reduction in growth in the field due to SCN. There are many questions about SCN on dry beans which we still need to answer, but the answers will only come with good research. We do not know at what levels of SCN in the soil (usually expressed as eggs per 100 cc of soil) dry beans will be damaged. It will probably depend on the bean class and environmental factors such as drought stress. There is another potential impact SCN could have on dry beans and that is the interaction of SCN with fungal root rot pathogens such as Fusarium and Rhizoctonia. Root rot pathogens cause important dry bean diseases in our area and SCN could exacerbate the root rot problem. It is well known in soybeans that SCN interacts with fungal pathogens on the roots. These are areas of research that we wish to investigate. In addition we need to look for sources of high levels of resistance in dry bean to SCN in case this becomes a serious problem in the future.
There are some steps growers can take to minimize the potential damage from SCN. First, learn what SCN is and how to identify it. If you are bringing in equipment from areas with SCN, thoroughly power wash to remove all the soil and debris. SCN is easily carried in soil on tires and equipment. If you suspect SCN in your fields, collect soil samples at random from the field, bulk the samples and send it to a laboratory to have the egg number determined. If you find that you have SCN, consider increasing the rotation time between susceptible crops to allow nature to naturally reduce the egg numbers. It is important to keep egg numbers low since there is generally a direct correlation between egg numbers and the amount of damage to the crop. Also, high egg counts take longer to reduce with crop rotation. As more research becomes available, there will be additional information on control of SCN.
For more information on SCN refer to these web sites: