The first noticeable symptoms of SDS are yellow, chlorotic blotches that form between the veins of soybean leaflets. These blotches expand between the veins into large, irregular chlorotic patches that later turn brown and die (Figure 1). Severely affected leaflets may drop off the plant, however the leaf petiole remains attached to the stem. Occasionally, bluish-white mass of SDS pathogen spores may be observed on the roots.
SDS foliar symptoms can be similar to brown stem rot (BSR), stem canker, and charcoal rot, however dead leaflets from these diseases tend to remain attached to the petiole. Also, SDS-infected soybean plants should have a white, decay-free pith when splitting the stem length-wise (Figure 2) compared to BSR infected plants which have a tan to brown pith at or near the crown and often at stem nodes (Figure 3). Although the pith remains white in SDS infected plants, the cortical tissue may exhibit tan to light-brown streaks.
Infected plants often have increased flower and pod abortion. SDS can affect entire fields of soybeans, but usually begins as scattered areas within a field.
The fungus overwinters in crop residue or soils. Infection can occur soon after planting but above-ground symptoms usually appear after flowering and during pod fill. SDS is favored by high-yield environments, cool and wet weather after planting, and compacted soils. In addition, moderate to high populations of soybean cyst nematode (SCN) can be associated with SDS and may increase the severity of the disease.
Yield losses from SDS range from slight to nearly 100% and are dependent on disease onset and severity. A management strategy should be developed before planting to help reduce infection. Foliar fungicide application have no effect on SDS suppression due to fungal infection occurring on the root system. An integrated management plan for SDS may include the following:
1 Westphal, A., Abney, T.S., Xing, L. and Shaner, G. 2008. Sudden death syndrome of soybean. The Plant Health Instructor. http://www.apsnet.org.
2 Robertson, A. and Leandro, L. 2010. Answers to questions about soybean sudden death syndrome in Iowa 2010. Iowa State University Extension. http://www.extesnion.iastate.edu.
Web sources verified 5/16/17.