Season 3, Episode 7 of Battle for the Belt is now available: https://www.youtube.com/watch?v=X5k8Y9eiXt0
In Episode 7, Dr. Horacio Lopez-Nicora, the Ohio State Soybean Pathologist and Nematologist, discusses soybean seedling diseases.
Figure 1. Disease triangle. Roth et al. 2020. Journal of Integrated Pest Management, 11(1): 17; 1–28.
For a disease to develop and be present in a field, there needs to be a susceptible host, the presence of a pathogen, and favorable environmental conditions (Figure 1). If these three requirements are not met, then the disease will not occur. Cool, wet weather often creates favorable conditions for many seedling diseases in soybean. However, certain soilborne pathogens can thrive and also cause severe seedling diseases in warmer soil temperatures.
This spring, the persistent wet weather across most of the state over the past few weeks has created ideal conditions for the onset of early-season soybean seedling diseases. In Ohio, we struggle with many soybean diseases that cause damping-off. Damping-off is the wilting of the seedling before emergence, called pre-emergence damping-off or the death of the seedling just after emergence, also called post-emergence damping-off.
Phytophthora and Pythium (Figure 2) are common water mold pathogens that cause damping-off. While it is common to expect disease establishment early in the spring, Phytophthora Sonae can infect plants later in the season, resulting in root and stem rots. The ideal environment for a water mold is saturated soils, wet conditions, and soil compaction. Both Phytophthora and Pythium have a different need when it comes to temperature, though, with Phytophthora requiring temperatures >60/70°F, while Pythium needs 50-60°F or 85-95°F. In this range of suitable temperatures, if your field has a history of these seedling pathogens and soils are saturated, the development of disease will be very likely, requiring integrated pest management techniques including seed treatments and choosing resistant soybean varieties.
Figure 2. Phytophthora Root and Stem Rot (left) and Pythium Seedling Blight and Root Rot (right).
While water molds are fungus-like organisms, our fields in Ohio also deal with true fungi such as Fusarium species, which cause Fusarium Root Rot, and Rhizoctonia solani, the causal agent of Rhizoctonia Seedling Blight (Figure 3). Early-season symptoms of water mold and fungal infections in soybean can appear similar, but distinguishing between them is crucial for selecting appropriate seed treatments. The active ingredients effective against water molds differ from those that protect against fungi, making accurate disease identification essential for effective management. Figure 4 illustrates this importance: soybean plants inoculated with Fusarium and treated with fungicides show effective control when using products specifically designed for true fungi, such as CAPTAN 400 or MAXIM 45. In contrast, APRON Max, designed for water molds, provides no control. Since both types of pathogens can coexist in the field, using a mixture of active ingredients can effectively manage each pathogen.
Final Considerations for Stand Reductions
Is disease causing poor stand establishment?
Many abiotic and biotic conditions can cause stand losses. Therefore, an accurate diagnosis of disease is necessary to determine the cause of stand loss.
Could the fungicide rate be the issue?
The fungicide rate could be a problem, so verifying that the seed treatment was applied appropriately is important.
Can the environment reduce treatment success?
Yes, if the seed has been sitting in cool wet soil for a long period of time, the efficacy can be reduced.
What else can help?
If there are multiple diseases and abiotic factors influencing stand, an integrated management approach is recommended. Well drained soil, resistant varieties, and a seed treatment labelled for the disease are the top management practices for limiting the severity of these diseases.
For more information on soybean seedling diseases please visit:
- An Overview of Soybean Seedling Diseases [https://cropprotectionnetwork.org/publications/an-overview-of-soybean-seedling-diseases]
- Seed Treatments: Questions that Emerge When Plants Don’t [https://cropprotectionnetwork.org/publications/seed-treatments-questions-that-emerge-when-plants-dont]
- Fungicide Efficacy for Control of Soybean Seedling Diseases [https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-soybean-seedling-diseases]
If you have any questions or issues in the field, please contact Dr. Horacio Lopez-Nicora with the information below.
If you notice any disease issues, please get in touch and send samples to the lab for analysis
Attn: Horacio Lopez-Nicora, Ph.D. (lopez-nicora.1@osu.edu)
Department of Plant Pathology – The Ohio State University
110 Kottman Hall – Soybean Pathology and Nematology
2021 Coffey Rd., Columbus, Ohio 43210
Crop Progress Updates from the Field
Due to rainfall, most of Ohio soils were saturated last week, impeding much of the state from planting, including our three research stations. Therefore, planting progress has been slow as of recently. We are looking forward to warmer weather and hopefully drier fields to have the opportunity to plant again this week.
Across all locations and planting dates, the corn is at the same stage, V2. Impressively, planting dates ranging between March 27th and April 18th, northern and southern Ohio, are similar in stage. Like corn, all the soybeans are at a similar stage, VC. However, soybean growth/emergence is less even while corn stands are more uniform, though, corn is still showing yellow coloration due to wet-cold conditions. Table 1 and Figure 5 show more crop progress details across sites, corn and soybean.
Table 1. Precipitation, soil temperature, average air temperature, cumulative GDDs, and stage at the Western Agricultural Research Station, the Northwest Agricultural Research Station, and Wooster Campus. Weather data retrieved from: https://weather.cfaes.osu.edu/.
|
Precipitation (Inches) (May 5 - May 11) |
2-inch soil temperature |
Air Temperature (May 5 - May 11) |
Planting date |
GDDs (Cumulative) |
Corn |
Soybean Growth |
|
|
Western, Clark County |
0.68
|
Min: 55°F Max: 72°F Mean: 55°F |
Min: 39°F Max: 79°F Mean: 58°F |
April 18 |
259 |
V2 |
VC |
|
Wooster, Wayne County |
1.07
|
Min: 55°F Max: 67°F Mean: 60°F |
Min: 55°F Max: 74°F Mean: 34°F |
March 27 April 18 |
255 195 |
V2 V2 |
VC VC |
|
Northwest, |
1.63
|
Min: 48°F Max: 67°F Mean: 57°F |
Min: 56°F Max: 79°F Mean: 35°F |
March 27 April 16/17 |
260 212 |
V2 V2 |
VC VC |
Corn pictured on the top and soybean on the bottom. Photos taken on May 9th.
If you would like to learn more, check out our research updates through C.O.R.N. article updates and YouTube Videos this growing season! You can find the full video playlist of Battle for the Belt on the Ohio State Agronomy YouTube channel.