Soybean cyst nematode [SCN] is one of the most if not the most damaging pests that afflicts soybean grown in the U.S. The damage caused by this pest is mostly confined to soybeans that are grown on medium-and coarse-textured soils. Methods used to control/manage this pest and its effect on soybeans are outlined in a White Paper on this website, and include rotation of soybeans with a nonhost crop such as corn and growing resistant soybean varieties on sites that are known to be infested with damaging levels of SCN.
An article titled “How to choose an SCN-resistant soybean variety” by Rod Swoboda appears in a recent issue of WallacesFarmer, a FarmProgress publication. Information in this article is gleaned from an Iowa State Univ. publication titled “Soybean cyst nematode-resistant soybean varieties for Iowa” by Dr. Greg Tylka and Mark Mullaney, which contains a list of SCN-resistant varieties for MG’s grown in Iowa [0 through late 3]. However, Midsouth soybean producers who are dealing with SCN infestations in their fields are encouraged to consider the below points from these articles [mainly from Dr. Tylka], as well as the information in the above-linked White Paper.
• Damage from SCN infestations is not usually detected visually. In fact, the first indication of an SCN-related problem in a given field may be an unexplained, lower-than-expected soybean yield.
• SCN reproduces rapidly on susceptible soybean varieties and can survive in the soil for 10 years or more even if soybeans are not grown on the site.
• Two sources of genetic resistance [PI88788 and Peking] to SCN are currently being used to develop SCN-resistant soybean varieties. However, most of the resistant varieties [~95%] that are currently being grown contain resistance genes from PI88788, and this resistance is rapidly breaking down.
• Varieties that contain resistance genes from another source such as Peking should be used where possible/if available because varieties with the Peking source of resistance are effective at controlling SCN populations. However, varieties with this resistance source should not be grown repeatedly on a site because SCN populations will overcome that resistance just as they have overcome PI88788 resistance. Thus, rotating varieties with differing sources of resistance is recommended.
• Resistance is very effective for managing SCN, but not all resistant varieties maintain high yields plus keep SCN populations low. Thus, soybean producers must rely on both how well a resistant variety yields as well as the effectiveness of a resistant variety at suppressing reproduction of SCN.
• All sources of SCN resistance allow limited reproduction of SCN, and this limited reproduction on a resistant variety does not pose a problem in a single growing season. However, if a variety or varieties with the same source of SCN resistance is/are repeatedly grown on an SCN-infested site, then a population of SCN that readily feeds on varieties with that source of resistance may build to damaging levels.
• Rotating soybeans with a non-host crop such as corn plus rotating soybean varieties with different sources of resistance is the widely-accepted recommendation for managing SCN.
• Since SCN can spread in wind-blown soil, it is recommended that SCN sampling still be conducted in fields with no history of SCN-related problems.
Composed by Larry G. Heatherly, Dec. 2023, firstname.lastname@example.org