ILSOYADVISOR POST

SCN and SDS - Two Soybean Pests Worthy of Your Attention

SCN and SDS represent large threats to soybean production in Illinois. Attend the upcoming webinar “Solutions to effectively manage SCN and SDS” sponsored by the Illinois Soybean Association and ILSoyAdvisor. Presenters will be Jason Bond, plant pathologist from Southern Illinois University and Nick Tinsley with Bayer Crop Science.

Sudden death syndrome (SDS) and soybean cyst nematode (SCN) are two of the most economically significant diseases affecting soybeans grown in Illinois and throughout much of the Midwest. In fact, the soybean cyst nematode (Heterodera glycines) and the pathogen that causes SDS (Fusarium virguliforme) have been documented in almost every state where soybeans are produced and have become a major challenge to manage.

Growers typically notice SDS during midsummer, when the aboveground symptoms of interveinal chlorosis begin to appear. These irregularly shaped yellow patches on the leaves eventually expand in size and then turn necrotic after a period of time. Once aboveground symptoms are noticed, yield loss is inevitable and cannot be recovered. What many growers may not realize is that infection occurs early during the growing season and that the pathogen that causes SDS also causes a root rot, resulting in an unhealthy root system. Accompanying high densities of SCN can result in poorly developed root systems as well, which may cause soybean plants to appear stunted and chlorotic. However, it is also not uncommon for plants infected by SCN to display no aboveground symptoms at all.

The environmental conditions promoting yield loss from SCN and SDS are quite different. Yield loss from SCN tends to be more pronounced during hot, dry summers. Conversely, yield loss from SDS tends to be more severe with cool, wet conditions following planting—these conditions favor infection by the SDS pathogen. Additionally, heavy rains and saturated soil conditions during midsummer promote the upward movement of toxins in plants affected by SDS, resulting in the familiar aboveground symptoms.

Depending on the year, yield losses from SCN and SDS can be variable. Because a soybean field can be infected with SCN without noticeable aboveground symptoms, yield loss is often underestimated. However, in heavily infested fields, yield loss from SCN can exceed 30 percent. The severity of yield loss from SDS depends on when the aboveground symptoms are first observed, with an earlier onset of symptoms resulting in greater yield loss.

Managing these two important pests can prove to be challenging. Rotating away from soybean is certainly effective for reducing densities of SCN; however, this practice fails to reduce the risk of SDS development. Resistant varieties are commercially available for both SCN and SDS. While varieties resistant to SDS help manage foliar symptoms, they do not protect against the root rot caused by F. virguliforme. Furthermore, there is growing concern about the inability of SCN-resistant varieties to manage SCN populations adequately. The primary source of resistance, PI88788, occurs in the vast majority of varieties and has since the 1990s. There are some areas where this source of resistance does not seem to be as effective as it has been in the past.

For growers concerned about preventing yield loss caused by SDS and SCN, ILeVO® seed treatment offered by Bayer has demonstrated consistent results since its commercialization in 2015. The active ingredient in ILeVO (fluopyram) has activity against the pathogen causing SDS, as well as nematodes in the seed zone. Complementing their current SDS and SCN management tactics with ILeVO seed treatment offers growers a solution to reduce risk and preserve yield potential.


Nick Tinsley


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