C.O.R.N. Newsletter: 2024-38

Following the aftermath of severe drought and Hurricane Helene, soybean farmers in Ohio have faced considerable challenges with stem, pod, and seed decay, leading to the occurrence of blackened soybeans in certain regions. This article serves as a follow-up to our previous report.

Understanding the Impact of Pod and Seed Decay on Soybean. The heavy rains following Hurricane Helene, which came after a severe drought, have created ideal conditions for fungal growth to negatively impact soybeans, especially those planted early (Fig. 1). These fields that matured early, already weakened by drought stress, became more vulnerable to fungal colonization, resulting in stem, pod, and seed decay. This "black soybean" phenomenon has been particularly noted in areas affected by this extreme weather pattern.

Key Findings:

1. Fungal Proliferation: The substantial rainfall accelerated the growth of fungi responsible for pod and seed decay. The primary pathogens involved are fungi from the Diaporthe/Phomopsis complex, Cercospora, Fusarium, and Alternaria. Alongside other saprophytic fungi, they contribute to the darkened appearance of affected soybean plants (Fig. 2).

2. Pod and Seed Decay: Drought-stressed pods are prone to shattering, which exposes seeds to fungal pathogens, leading to prominent decay (Fig. 2). Field areas that experienced higher evapotranspiration during the drought, such as hilltops, show more pronounced darkening, whereas areas with higher humidity, like lower regions, exhibit less discoloration.

3. Germination Challenges: At the Soybean Pathology and Nematology Lab of Ohio State University, a significant reduction in seed germination rates was observed due to fungal infections from "black soybean" compared to healthy-looking soybean plants. Infected seeds not only demonstrate reduced germination potential (Fig. 3) but also decreased storability and weight.

4. If you suspect a soybean disease, send samples to diagnostic labs before plant senescence. Early testing is crucial, as post-maturity colonization by saprophytic organisms, including fungi, complicates accurate diagnosis. For example, mature plants with black discoloration were submitted to the lab. Upon closer examination, the fungus responsible for white mold (more here) was identified as the primary causal agent, while secondary fungi were found colonizing the plants post-mortem (Fig. 4).

Read more about soybean seed quality (here) and about pod and stem blight and seed decay (here and here). We are happy to assist with diagnosis. You can send your sample to:

OSU Soybean Pathology and Nematology Lab

Attn: Horacio Lopez-Nicora Ph.D. 110 Kottman Hall 2021 Coffey Rd. Columbus, Ohio 43210 lopez-nicora.1@osu.edu

Strategies for Mitigating Pod and Seed Decay: As the 2025 growing season approaches, start by selecting pathogen-free, disease-resistant soybean seeds to enhance crop resilience. Consider the use of fungicide seed treatments to prevent disease transmission from seeds to seedlings. Implement crop rotation with non-host plants to reduce soil-borne pathogen levels and lower future outbreak risks. Integrate pest management (IPM) strategies to control pests like bean leaf beetles and aphids, which can introduce viruses and facilitate fungal infections. These measures collectively strengthen soybean crop health and productivity, though unpredictable weather events, like this year's drought followed by heavy rainfall, can still pose challenges.

Conclusion. Ohio's extreme weather conditions—ranging from severe drought to heavy rains following Hurricane Helene—have posed significant challenges regarding stem, pod, and seed decay in soybean production. Consider how varietal selection and seed treatment decisions made this winter could impact risks for infection in the coming year. By implementing robust management practices and maintaining vigilant monitoring, we can protect our crops, maximize yields, and ensure a more stable future for soybean production.