By Nathan Kleczewski
We have seen soybeans that are exhibiting foliar symptoms that could be concerning to some people. Unfortunately, Sudden death syndrome (SDS) has been claimed to be the culprit for these issues when in all likelihood it is not. What might you see out there and what is the likely cause?
Several growers have noticed areas of fields such as turnrows, entrances, and field edges with beans that have yellowing foliage and interveinal chlorosis (the area between the veins is yellow or even brown). What you are looking at are water stressed beans that are senescing earlier than the beans in the surrounding parts of the field. These areas also are often compacted, leading to water stress issues. Plants in compacted areas also tend to have roots that flare out and are shallow, another indicator that SDS is not the culprit.
Other people have noticed interveinal chlorosis throughout the field. Check your soil, as we have found this to be associated with severe nutrient deficiencies (such as manganese or magnesium) (Figure 1).
Figure 1. Some severe nutrient deficiencies can cause foliar symptoms that appear similar to SDS.
So how can you tell if you have SDS? First, SDS requires a large slug of water at planting and typycally cool temperatures to infect. This year we did not have conditions highly conducive to SDS. Second, with one exception, we have not seen widespread SDS as has been observed in the Midwest. This is likely due to the higher sand content of our soils. Typically SDS infections occur in irregular patches, often in poorly drained areas of the field. The foliar symptoms are a result of toxins that are produced by the fungus after infecting the roots and stem. These toxins move with the water flow of the plant into the leaves and burn out the leaves (Figure 2). Third, SDS causes the vascular tissue to brown. Nutrients or drought will not cause this symptom. In addition, after wet weather you will see blue growth at the soil line or in the root zone (Figure 3). Again, this will not be observed in nutrient or drought stressed plants.
Figure 2. Sudden Death Symptoms on a soybean leaf.
Figure 3. Blue growth on the root and soil line is indicative of Sudden Death Syndrome.