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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.
Figure 1. SDS initial leaf symptoms.
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.
Figure 2. Severe SDS leaf symptoms with a split stem exhibiting white pith.
Figure 3. Soybean stem split lengthwise showing the brown pith in the stem from BSR.
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:
ILeVO® seed treatment is a management tool that can reduce the severity of SDS. Consider this product if you are planting into fields that have a history of SDS.
For SCN management consider NemaStrike™ Technology, a seed treatment technology that provides broad-spectrum nematode control, including SCN, for soybean, corn, and cotton crops. Other nematodes controlled include root knot, lesion, lance, reniform, sting, and needle.
With a novel mode of action and low water solubility, this synthetic nematicide (tioxazafen), NemaStrike™ Technology defends crops from the start and stays in the root zone as plants grow for up to 75 days. In numerous field trials over 4 years, the technology has helped to protect the average yields of soybean by 2.2 bu/acre (138 trials), corn by 6 bu/acre (140 trials), and cotton by 80 lbs lint/acre (63 trials).1 Performance results will vary based on nematode pressure.
Acceleron® Seed Applied Solutions with NemaStrike™ Technology will be offered to DEKALB® and Asgrow® brand seed purchasers. Please contact your DEKALB and Asgrow brand seed providers for additional information.