For nearly 40 years, sudden death syndrome has ranked second only to soybean cyst nematode in damage to soybean crops. DuPont Pioneer research shows that, in extreme conditions, this root-rotting disease can cause yield losses as high as 80 percent.
"SDS varies in severity from area to area, and from field to field, but as a result of the cool, moist soil conditions earlier this season there may be a higher incidence of SDS in soybeans this year," says Jeff Thompson, DuPont Pioneer senior research manager. "Growers must understand clearly the extent of infection in each of their fields to effectively manage this disease so scouting becomes essential."
Disease severity depends on environmental conditions, time of infection and other stresses on the soybean crop. This year may result in a higher incidence of SDS in soybeans as a result of cool, moist soil conditions early in the growing season. Though SDS infects soybean plants just after germination and emergence, symptoms usually do not appear until midsummer.
The development of symptoms is often linked with weather patterns of cool wet conditions early on followed by warm temperatures and high rainfall during flowering or pod-fill.
"Symptoms begin as small pale-green spots during flowering, just before pod-fill," Thompson says. "And the most visible symptoms will occur as necrotic lesions during pod-fill, when plants are focused on water uptake and sending nutrients to the developing seed."
Usually observed 10 to 14 days after heavy rains, root symptoms include rotted roots with deteriorated taproots and lateral roots. The root cortex will show light-gray to brown discoloration, and if soil moisture is high, sometimes bluish fungal colonies are present. These symptoms signal reduced water and nutrient uptake by the plant.
Leaf symptoms of SDS first appear as yellow spots, usually in a mosaic pattern on the upper leaves. The yellow spots coalesce to form chlorotic blotches between the leaf veins and the affected leaves will twist and curl before falling from the plant prematurely.
As soybean plants lose leaf area and their roots deteriorate due to SDS, their yield-making components are damaged. Flower and pod abortion are common, which results in few pods and seeds. Seeds may also be smaller and late-forming pods may not fill or mature. Pioneer experts recommend several management options to combat these effects year after year.
Management practices for SDS include selecting tolerant varieties, planting disease-prone fields last, improving field drainage, reducing compaction, maintaining proper fertility on fields, evaluating tillage systems, and reducing other stresses on the crop.
"Growers should also scout their fields for SCN because there is a tendency for products susceptible to SCN to display more severe SDS symptoms," Thompson states.
Not only does SCN increase stress on soybean plants, it also creates wounds through which the SDS pathogen can enter the roots. If you discover SCN in your fields, consider planting a high SCN- and SDS-tolerant soybean variety in the future.
Another SDS detection tool you can rely on is the new Pioneer Field360 Notes app. The app will help you track SDS field history and assist with scouting. It streamlines and organizes field-by-field agronomic information for communication among DuPont Pioneer agronomists, sales professionals and growers, and is compatible with all tablets and mobile devices.
For more information on SDS scouting tips or management options contact your local DuPont Pioneer agronomist or Pioneer sales professional or visit pioneer.com.