Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Full season soybeans across the area are approaching or at R3. Overall, soybean disease pressure has been low across the region. I have been seeing a bit of low canopy Septoria Brown Spot. Leaf symptoms begin as small brown spots that can have a yellow halo around them, as spots coalesce the leaf may turn yellow (Figure 1). This disease usually stays to the bottom of the plant, limiting yield impact. Fungicide applications in soybean are most economical when disease is present and fungicides are applied during R1-R6 growth stages, with R3 being the most common timing. If you have disease present, and are considering a fungicide application, it is important to scout fields and monitor the weather. Most soybean diseases are favored by humid, wet conditions. If weather patterns continue to be hot and dry, disease pressure will likely remain low. However, we do often see wet falls, so continue to monitor rainfall and disease pressure through R6. The 2022 National Fungicide Efficacy Recommendations for Foliar Diseases of Soybean can be found at https://cropprotectionnetwork.s3.amazonaws.com/CPN1019_FungicideEfficacyControlSoybean_final2.pdf.
Figure 1. Low canopy Septoria brown spot