Published on Wednesday, May 31, 2017
Did you know that Septoria brown spot (SBS), also know as brown spot, is the second biggest disease threat to soybean yield after soybean cyst nematodes?
Since SBS has the potential to reduce soybean yields more than most farmers and agronomists realize, it's important to implement additional attention and control measures to manage this disease.
SBS is a fungal leaf spot caused by Septoria glycines, a common disease of soybeans not only in Illinois, but throughout the entire Corn Belt. Nearly every soybean field in Illinois experiences some level of brown spot infection each year. For years however, many of us never considered this disease to be a real threat to our soybean yields.
Warm, moist weather conditions, combined with high humidity and poor drainage, favor the development of brown lesions on lower leaves. These lesions can reinfect and move upward through the canopy. Moderate to severe infection can lead to premature senescence and leaf defoliation, resulting in loss of stored nutrients, smaller seed size with lower seed weight, and yield reduction.
In Illinois, the soybean diseases typically associated with the greatest yield losses include soybean cyst nematode (SCN) and sudden death syndrome (SDS). While yield loss estimates continue to indicate SCN is the number one yield thief in Illinois, estimates provided by the North Central Soybean Research Program in 2015 show that SBS was the number two cause of yield loss. In Illinois in 2015, SCN was estimated to have caused yield loss upwards of 18.8 million soybean bushels, while SBS caused yield loss of 12.5 million bushels. By comparison, SDS was estimated to cause 6.2 million bushels of yield loss.
Septoria brown spot (SBS) infection on lower soybean leaves.
Picture taken June 15, 2016 in Champaign County, IL
These staggering yield loss estimates suggest SBS requires more attention and management for high-yielding soybeans than previously thought. In most years, I haven’t considered SBS to be a significant yield-limiting factor because it usually stayed lower in the canopy without much upward progression throughout the growing season. Therefore, we generally never see it. But think about it for a minute. A lot of the yield on a soybean plant comes from the middle of the plant and the foliage that resides there. The unobserved presence of SBS may have a bigger impact on yield than we previously thought.
A recent review of SBS research in scientific literature suggests that yield losses can vary based on several factors. These include genotype vulnerability, environmental conditions (rainfall and drainage), timing of infection, and use and timing of a fungicide application. Uncontrolled, natural infections of SBS in field trials over the past four decades have resulted in yield losses of up to 10.2 percent.
Research and farm practices have revealed that applying a fungicide (strobilurin, triazole or a combination of strobilurin + triazole) near the R3 growth stage (beginning pod) has been effective at reducing SBS infection and preventing yield loss when infections occur later in the season.
Research has also indicated that an infection of SBS during early vegetative stages, as early as V2 to V8 and before R1, can lead to greater disease pressure and yield loss than initiation of infection during mid-reproductive growth stages (R3 to R5). Infection of SBS is common in Illinois soybean fields during early vegetative stages. As previously mentioned, disease progression depends on varietal tolerance, rainfall during early vegetative studies, and adequate soil drainage.
This information raises many valid questions regarding the need to better manage SBS to increase soybean yields.
These are all questions we will look to answer. If you have any questions about SBS, please contact your local Beck's seed advisor or dealer.
Author: Chad Kalaher
Categories: Agronomy, NW Indiana, E Central Illinois
Beck’s Hybrids team sales agronomist for 22 counties in NE ¼ of IL and 7 counties in NW IN. Raised on grain and livestock farm in southern IL. B.S. Agronomy 1995 – University of Illinois, M.S. Weed Science 1997 – North Carolina State University. Previous positions in seed industry as researc
Beck’s Hybrids team sales agronomist for 22 counties in NE ¼ of IL and 7 counties in NW IN. Raised on grain and livestock farm in southern IL. B.S. Agronomy 1995 – University of Illinois, M.S. Weed Science 1997 – North Carolina State University. Previous positions in seed industry as research agronomist, district, and regional sales manager.