Soybean Disease Update--March 2025
In a previously-posted article on this website, results from multi-year strip trials that were conducted in Missouri were summarized. The conclusion from this research is that the prophylactic foliar fungicide application that is applied by many producers at soybean stage R3 is usually not a profitable activity–i.e. the return on investment [ROI] was not positive in a large percentage of the cases. Rather, all soybean fields should be diligently scouted for the presence of disease(s) and the appropriate fungicide applied only if needed to protect yield and the technology, and to result in a positive ROI. Other tips for managing soybean diseases follow.
• Click here to see the major diseases that affect Midsouth soybeans. Click here to access a Disease Management White Paper that is posted on this website.
• Use a contact + systemic fungicide seed treatment on all soybean seed that are to be planted regardless of planting date. Click here to access a Seed Treatment White Paper on this website.
• Check out the Crop Protection Network [CPN] website for information that is included in publications, tools, and resources such as a Foliar Fungicide Efficacy Table.
• Click here to access the most recent “Fungicide Efficacy for Control of Soybean Seedling Diseases” that has been compiled by the CPN.
• Frogeye leaf spot [FLS] disease will significantly reduce yield of susceptible varieties, but its effect has been curtailed in Midsouth soybean fields because of the use of varieties that are resistant to the causal agent. If FLS is present in a yield-limiting amount, fungicides that contain a FRAC code 3 component should be used as a curative treatment.
• Sudden Death Syndrome [SDS] is not a problem disease in Midsouth soybeans at this time. However, fields should be scouted for its presence since it can significantly limit yield if present.
• An article titled “10 factors fields with SDS have in common” provides information from Dr. Daren Mueller, Extension Plant Pathologist at Iowa State Univ., who headed a project through the CPN to determine where SDS would be most likely to occur. The list was headed by soils with a pH above 6.5, and also included fields that had soybean cyst nematode [SCN] eggs present.
• Soybean Cyst Nematode and Root Knot Nematode [RKN] are nematode species that will reduce Midsouth soybean yields if not managed properly. Click here to access a White Paper titled “Managing Nematodes in Midsouth Soybeans” that provides pertinent information about the occurrence and management of both SCN and RKN.
• Rotation of soybeans with other crops is a key component of both SCN and RKN management, but rotation with non-host crops is different for the two nematode species. Check the above-linked White Paper to see appropriate crops to use in rotation if either nematode species is present.
• Where SCN is a recurring problem, producers should plant a variety with Peking resistance since SCN population adaptation to the PI 88788 resistance source that is used in most SCN-resistant varieties has become common.
• Syngenta is set to launch Victrato seed treatment for the 2025 growing season, pending regulatory approval from the US-EPA. It is being marketed for use at cropping sites with high pest pressure from several nematode species–including SCN and RKN–and diseases such as SDS. Its active ingredient is cyclobutrifluram, which has an SDHI mode of action.
• Nematicides should only be used in combination with the accepted nematode-management practices of crop rotation and use of resistant varieties. See the above-linked Nematode White Paper for more information.
Composed by Larry G. Heatherly, Mar. 2025, larryh91746@gmail.com