As you are driving around the county you may begin to notice yellow patches popping up in soybean fields. This can be attributed to several things; early senescence, brown stem rot, charcoal rot, or sudden death syndrome. While we have seen each of these things this year, the most common culprit is sudden death syndrome. This blog will be focused on sudden death syndrome, or SDS, and what we can do about it.
What is Sudden Death Syndrome (SDS)
Sudden death syndrome is a soil borne disease caused by the fungus fusarium virguliforme. This fugus overwinters in the soil and in residue. Come spring, it will infect soybean plant roots ultimately resulting in the symptoms we see in the field. Infection can occur days after the seedlings germinate. SDS is favored by cool, wet environments. Irrigated, high yielding fields also favor disease development. Additionally, fields higher in sand content, lower pH, and with higher phosphorus levels also may favor development. Yield impact can range from very minimal, to complete yield loss based on time of infection and quantity of inoculum. SDS moves on residue in flood waters, or transported on equipment from field to field.
Symptoms of Sudden Death Syndrome
SDS is characterized by development of chlorotic or yellow areas on the leaves of the plant between veins. As the disease progresses, the chlorotic spots will become necrotic (brown) and can eventually cover the entire leaf. If it progresses that far, this will often result in premature leaf drop. The foliar symptoms are not a result of the disease itself but rather a toxin that is produced in the roots and translocated to the leaves. The fungus never moves more than a few inches from the crown of the plant. Additionally, foliar symptoms are not manifested until the soybeans are at the podfill stage.
Symptoms also show up on the root system. A generic looking rot may appear on the tap root. In heavily infected plants, the fungus may also show up as blue growths on the root system. The root system symptoms can easily be confused with brown stem rot. Cut open the tap root and look at the inside of the stem. Plants infected with SDS will retain a white pithy interior, while brown stem rot will be obvious as a brown rotted interior.
Pod fill is reduced in plants with SDS. Size of beans will be reduced in minor infections. In locations with heavier pressure, pod fill may be aborted and pods will fall off the plant.
Fields that have Soybean Cyst Nematode can also result in worse levels of SDS. The SCN creates entry points for SDS and increases the amount that is able to enter the plant. If you have moderate to high levels of SCN in your field, be on the lookout for the impacts of SDS.
Management
Because SDS is a soil borne disease, it will always occur in the same location from year to year. This consistency is very useful in knowing which locations in the field are at risk and what areas need the most management. Site specific management is possible with the predictable nature of this disease.
A variety with a good SDS score should be planted. No variety is completely resistant to the disease, but several varieties such as P31A22, and P38A98 are rated particularly high for disease resistance. Quite a few other varieties provide a moderate level of resistance to SDS.
Early planting will encourage SDS development, so in heavily infected fields, a delayed planting date may be beneficial. Crop rotations can also help with inoculum levels, however the fungus can overwinter below freezing temperatures and can stay in the soil without a host for many years, so this cultural practice should not be used as the only means of management. Additionally, many other legumes are host crops. Research the list of host crops before planting a covercrop with a host species included. Some research shows that tilling the soil can reduce infection levels by eliminating compaction and helping warm the soil quicker. However, this also could serve to spread the disease to a larger portion of the field.
ILeVO
There has been one particular product that has been shown to dramatically reduce the effects of SDS on both foliar symptoms and overall yield impact. This seed applied product is called ILeVO from Bayer Crop Sciences and uses the active ingredient fluopyram.
Pioneer Seeds conducted a study covering 91 locations across 4 years testing the efficacy of ILeVO at two different rates compared to a standard seed treatment. These studies showed an average of 1.4 bushels per acre advantage with a half rate of ILeVO over a standard treatment. When applied with the full rate of ILeVO, there was a 2.0 bushel per acre advantage over the standard seed treatment. In locations classified as moderate to high levels of SCN and SDS, the full rate resulted in a 6.4 bushel per acre advantage to the standard seed treatment.
Three studies from the University of Nebraska On Farm Research Network tested ILeVO. Two of the studies resulted in a 2.8 to 3.7 bushel per acre advantage. One site had very low disease ratings and consequently had no difference in yield impact.
The price per acre of ILeVO may be a limiting factor for some operations. If historical distribution of SDS is well known in a field, site specific application may be possible to reduce input costs but still provide the level of protection needed for the areas with SDS. A study from the University of Nebraska utilized a multi-hybrid planter to site specifically place ILeVO seed treatment in portions of the field with past levels of SDS. Three fields had low levels of disease pressure in the study years and showed no difference in seed treatment. One field had moderate to high levels of SDS pressure and resulted in a 9 bushel per acre advantage in the portion of the field with historical levels of SDS and no difference in yield in the part of the field with no history of SDS. At this field site, the seed treatment resulted in a $78 per acre benefit. These results are exceptional and not likely in most cases. This case study does go to show the benefit that is possible in situations with very high levels of SDS.
Next Steps
Do you have any fields with SDS? Do these also have SCN? Some of the next steps would be to visually identify distribution of SDS within your field. Verify this distribution with both aerial imagery and yield data. Pull soil samples to send to a University to check for SCN populations. Higher levels of SCN will often warrant treatment. Next, select a variety with higher levels of resistance for the field. Finally, talk with a member of the Pederson Seed Team to discuss the use of ILeVO for your acres with SDS. While a permanent fixture in some fields, management techniques are available to help deal with the effects of Sudden Death Syndrome. What steps have you taken to deal with Sudden Death Syndrome in Soybeans? Leave a comment below!
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