Soybean Sudden Death Syndrome (SDS) is epidemic in Doniphan and Atchison counties this year and is at record levels in many other counties in northeast Kansas. The heavy rains following planting in early June combined with continued rain events in the northeast part of the state in recent weeks have provided ideal conditions for the disease to develop.
SDS is a disease caused by the soilborne fungus Fusarium virguliforme. This fungus prefers wet conditions and thus is usually most severe in irrigated fields. In 2014, however, it is equally bad in non-irrigated fields including not only bottomland fields but upland fields as well. SDS tends to be most severe on well-managed soybeans with a high yield potential. It also tends to be more prevalent on fields that are:
- Infested with soybean cyst nematode
- Planted early when soils are wet and cool
- Compacted
This year, SDS disease is severe in the Kansas River Valley from Geary County to the Missouri border and northeast Kansas in the Missouri River basin area. The disease can also be found in irrigated fields in the Republican River Valley northeast of Clay Center. SDS is even showing up in some areas of southeast Kansas.
Historical yield losses from this disease are generally in the range of 1 to 25 percent but it would not be surprising to see losses in the 50% range in the most severely affected fields this year. If yields on SDS-free fields are in the range of 60 bushels per acre, that means up to 15 - 30 bushels per acre could be lost to the disease on the most severely affected fields.
Symptoms of SDS are fairly easy to recognize. SDS begins as small, bright, pale green to yellow circular spots on the leaves during late vegetative or early reproductive growth stages. As the disease progresses, the tissue in these spots starts to die and enlarges to form brown streaks between the veins. Symptoms are more pronounced on top leaves.
Figure 1. Scattered yellow spots on some of the greener leaves in the lower right in this photo are the early leaf symptoms of SDS. The leaves in the center foreground have more advanced symptoms of SDS. Photo by Stu Duncan, K-State Research and Extension.
Figure 2. A soybean field in Franklin County with SDS. Photo by Eric Adee, K-State Research and Extension.
Flowers and pods may abort or not fill. Another key symptom of SDS is substantial amounts of root decay and discoloration of roots and crown.
Figure 3. Root rot occurs on plants infected with the SDS pathogen. This symptom distinguishes SDS from brown stem rot and stem canker. Left image by Jim Shroyer, K-State Research and Extension; right image courtesy of Iowa State University.
Diseased plants are easily pulled out of the ground because the taproots and lateral rots have deteriorated. Symptoms present on both the leaves and roots are diagnostic for SDS.
Soybean yield losses from SDS depend on variety and stage of crop development when the symptoms first appear. Appearance of the disorder at early pod fill is more damaging than its appearance at a later stage of plant development. Yield reduction is the result of reduced photosynthetic area, defoliation, flower and pod abortion, and reduced seed size.
Effective management of SDS requires an integrated approach. Management starts with the planting of SDS resistant varieties. At K-State, we have been evaluating soybean varieties for SDS resistance in our performance test for the past several years. Most varieties are susceptible to some degree, and very few have good resistance. The most susceptible varieties yield 40 to 50 percent less than the resistant varieties at locations where SDS is present and yield levels are in the range of 60+ bushels per acre.
Figure 4. The variety on the right in a recent K-State performance test was susceptible to SDS. The foliage was completely dead by early pod fill. Photo by Bill Schapaugh, K-State Research and Extension.
Seed companies also have SDS ratings for most of their varieties, and there is typically a wide variation in ratings. There is little or no correlation between the maturity of a variety and its SDS resistance rating.
The presence of SDS is strongly correlated with the presence of soybean cyst nematode. Therefore, where SDS is present, soil samples should be taken to determine the level of soybean cyst nematode present and it will need to be managed along with the SDS. Producers cannot manage SDS simply by selecting varieties that have soybean cyst nematode resistance, however. Some varieties with resistance to soybean cyst nematode are susceptible to SDS. And some varieties that are susceptible to soybean cyst nematode are resistant to SDS. Ideally, producers should select varieties that are resistant to SDS and multiple races of soybean cyst nematode.
Cultural management practices that can reduce the risk of SDS infection include delaying planting until soil temperatures are warmer, avoiding planting into overly wet soils, and reducing compaction problems within a field. Producers who have fields with compaction problems should make every effort to correct that problem before planting soybeans next season.
Crop rotation also seems to have some positive effect on SDS, but only if the field is not planted to soybeans for four years or more.
Recent research with seed treatments on soybeans has shown some promising results. A study with seed treatments applied to soybean was conducted at the Kansas River Valley Experiment Field in 2013, with treatments applied to three soybean varieties of with different levels of tolerance to SDS. The study was irrigated earlier and more often than normal for soybean to promote the disease. The most severely infested plots had more than 80% of the leaf area expressing symptoms of SDS by the R6 growth stage. Treatments with the experimental product ILeVO from Bayer CropScience reduced the amount of foliar disease in all varieties and increased yields up to 16 bu/acre, or more than 40% (Table 1). ILeVO is not yet on the market.
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Table 1. Influence of soybean variety and seed treatment on Sudden Death Syndrome, Kansas River Valley Experiment Field-Rossville, 2013 |
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Soybean varieties |
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Most resistant |
Moderately resistant |
Susceptible |
Most resistant |
Moderately resistant |
Susceptible |
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Seed treatment |
Yield (bu/acre) |
% Leaf area with SDS at R6 |
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None |
28.6 |
29.2 |
21.3 |
18% |
44% |
63% |
|
ILeVO* at 0.25 mg/seed |
41.6 |
39.7 |
37.4 |
4% |
28% |
45% |
|
ILeVO at 0.15 mg/seed |
42.9 |
41.0 |
26.2 |
5% |
28% |
72% |
|
LSD 0.05 |
8.3 |
17.4 |
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* Fluopyram 600 FS, Bayer CropScience
Doug Jardine, Extension Plant Pathology
jardine@ksu.edu
Bill Schapaugh, Soybean Breeder
wts@ksu.edu
Stu Duncan, Northeast Area Crops and Soils Specialist
sduncan@ksu.edu
Eric Adee, East Central Experiment Field Agronomist-in-Charge
eadee@ksu.edu
Doug Shoup, Southeast Area Crops and Soils Specialist
dshoup@ksu.edu
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
ciampitti@ksu.edu
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