Soybean Disease Management with Fungicides, Plus 2024 Production
In today’s soybean production environment of high and/or increasing input costs, the question “Is disease management in soybeans worth the cost” is often asked. For many years, use of late-season applications of foliar fungicides has been promoted by some to improve plant health with the subsequent result of increased seed yield. The conduct of a multi-year study in Missouri and its results offer guidance for managing diseases that affect soybeans.
• Multi-year strip trial research that was sponsored by the Missouri Soybean Merchandising Council and Univ. of Missouri Extension was conducted on farmer fields in Missouri.
• Commonly used foliar fungicides were applied to soybeans at stage R3 in strip trials that were located in all sections of the state.
• Results showed that spraying soybeans with a fungicide as a routine practice does not yield a positive return on investment [ROI] most of the time. In fact, the average yield increase of about 1.8 to 3.0 bu/acre was not enough to cover the cost of the fungicide application in most cases. Only 21% of the trials showed yield increases ≥3.3 bu/acre.
• In the strip trials, diseases such as septoria brown spot [does not typically result in yield loss] and FLS were present, but the severity levels were often too low to justify a fungicide application.
• A survey of Missouri farmers conducted by Dr. Mandy Bish found that about 65% of the state’s soybean acres receive a fungicide application, but only about 10% of these acres were scouted for disease presence before spraying. The preventative spraying that occurred in the state was usually done to control or manage FLS.
• The findings from this research are similar to research with fungicide application in other states, where applying foliar fungicides to soybeans resulted in only an average 2.7% yield increase in 90% of cases.
• These results lead to the following conclusions. 1) Using foliar fungicides when they are not needed will speed up/intensify resistance development to a fungicide in disease pathogens. 2) The uncertainty of the soybean market, the low yield response and negative ROI in most cases, and increasing cost of inputs means that soybean farmers must use scouting to determine the need for a foliar fungicide application vs. a prophylactic application. 3) Scouting for disease presence should be conducted before fungicide application. 4) When possible, soybean varieties with genetic resistance should be planted where the presence of a problematic disease is known or expected.
Overall, the preponderance of data defy the common belief that automatic or prophylactic fungicide applications during soybean reproductive development contribute to significant yield increase and profitability. This means that scouting should be used to determine the need for a fungicide application that will protect against significant yield loss. This will reduce the overuse of foliar fungicides which should in turn protect the technology so that it will be effective when actually needed to control a severe disease outbreak in soybeans. Click here to access a White Paper that provides information about disease management in soybeans.
Midsouth Soybean Production. According to USDA-NASS, Arkansas, Mississippi, Tennessee, and Louisiana, respectively, produced the 10th [166,100,000 bu.], 12th [127,120,000 bu.], 16th [75,600,000 bu.], and 18th [55,120,000 bu.] most bushels of soybeans in the U.S. in 2024. Harvested acres in the respective states were 3.02, 2.27, 1.80, and 1.06 million. The production and harvested acreage of the combined four states were 9.7% and 9.5% of the U.S. totals, respectively. Click here to access a White Paper that shows how the average soybean yields of the four states compare to the national average over the last 10 years.
Composed by Larry G. Heatherly, Mar. 2025, larryh91746@gmail.com