We are receiving reports on white mold and sudden death syndrome (SDS) appearing on soybeans in South Dakota.
The soybean plants are in the R3 – R5 development stage (pod development and fill), and the current weather conditions are favorable for development of both diseases. Additionally, the presence of inoculum (pathogen) and use of a susceptible variety will allow these diseases to work their way up the canopy and compromise yield.
White mold can be a problem on soybeans in fields where plant populations are high, row spacing is narrow, and the canopy closes early. In-season options for managing white mold in at-risk fields are very limited at this time. Fungicides are most effective to manage white mold when applied at, or close to R1 (flowering) and up to R3 developmental stage (pods are 3/16-inch long at one of the four uppermost nodes). However, late applications or fungicide applications when the disease shows up is not effective. For information on which fungicides are labeled, please refer to Foliar Fungicide Efficacy for Control of Foliar Soybean Diseases or the 2015 Soybean Pest Management Guide.
Consider planting soybean varieties with moderate resistance to white mold; these are available for maturity groups 0 through II. However, there are no soybean cultivars yet with complete resistance to the white mold pathogen (S. sclerotiorum). Check with the seed companies to get information on which soybean varieties for South Dakota are tolerant to white mold. Crop rotations with corn, small grains and forage legumes can reduce the number of sclerotia (hardened fungal mycelium) in soil (Figure 1).
Sudden Death Syndrome (SDS)
The SDS pathogen has been detected at low levels in samples from multiple South Dakota counties. With the current weather conditions continuing to be cool, there may be the possibility of the disease picking-up over time.
Symptoms of SDS usually show up in spots or scattered areas throughout the soybean field. The disease first appears as yellow between the leaf veins. This leaf tissue dies becoming brown in color and the leaf veins remain green. As the disease progresses the yellow and brown areas become large irregular shaped lesions (Figure 2). There are no in-season options available for SDS management. Foliar fungicides are not effective since SDS originates from the root system. For more information on SDS, refer to Sudden Death Syndrome on Soybean on iGrow.
Submitting SDS Samples
If you identify SDS in your field or have one of the SDS-like symptoms and are not sure what the disease may be, please consider sending samples to the SDSU Plant Science Department. Our labs are set-up to run tests to confirm for SDS in soybean samples. Additionally, these samples will be used in the SDS management research conducted by Mr. Paul Okello and Mr. John Posch (graduate students supported by the South Dakota Soybean Research and Promotion Council and the North Central Soybean Research Program).
The best way to submit soybean samples is:
- Collect at least 3 plants (including roots) showing SDS or SDS-like symptoms. The plants should not be wet with rainfall or dew. If they are wet, please allow the sample to dry before they are packed.
- Please include information on location (GPS, county), tillage, growth stage and previous crop.
- Please send samples to:
SDSU Extension Oilseeds Plant Pathologist
South Dakota State University
113 Plant Science Building (SPSB), Box 2108
Brookings, SD 57007