Soybean Disease Updates

Alyssa Koehler, Extension Field Crops Pathologist;

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. With the recent rain it may increase foliar disease pressure. The 2023 National Fungicide Efficacy Recommendations for Foliar Diseases of Soybean provides an overview of product ratings based on trials conducted by Extension specialists across the country (Figure 2).

Soybean with Septoria Leaf Spot on the Bottom

Figure 1. Low canopy Septoria brown spot

Chart of Fungicide Efficacy on Soybeans

Figure 2: 2023 Fungicide Efficacy Ratings for foliar diseases of soybean (