Recent years of dry growing conditions have reduced the occurrence of sudden death syndrome (SDS) in soybean fields. Yet, DuPont Pioneer soybean scientists warn that cool spring soils and high rainfall in areas of the Corn Belt may lead to a midsummer appearance of SDS symptoms.
Fortunately, Pioneer soybean research has tested for SDS since 2001 and continues to develop Pioneer brand soybean varieties with high tolerance to the disease.
“Since the research program was initiated, the number of Pioneer brand soybean varieties with a SDS tolerance score of five or greater has grown from 20 percent of all varieties to more than 80 percent,” says Steve Schnebly, DuPont Pioneer soybean researcher. The testing program focusing on SDS was added as soybean researchers identified field infections spreading from the southern Corn Belt to north and east.
The severity of SDS depends on environmental conditions, time of infection and other crop stressors. Although SDS infects soybean plants just after germination and emergence, symptoms generally do not appear until midsummer.
Soybean SDS varies in severity from area to area, and from field to field. That’s why growers must clearly understand the extent of an SDS infection in each of their fields to effectively manage the disease. This requires scouting fields when disease symptoms are present, ideally using GPS tools like Encirca View to map SDS-prone areas. Encirca View maps can be overlaid with yield maps to reveal the extent of yield losses from SDS. Check pioneer.com for information about Encirca services. For a free download of Encirca View, go to encirca.pioneer.com.
SDS leaf symptoms first appear as yellow spots, usually in a mosaic pattern on upper leaves; the yellow spots coalesce to form chlorotic blotches between leaf veins. Infected leaves, appearing about midseason, twist and curl before falling from the plant prematurely.
Root symptoms include rotted roots with deteriorated taproots and lateral roots. The root cortex shows light gray to brown discoloration; if soil moisture is high, sometimes bluish fungal colonies are present. These symptoms signal reduced water and nutrient uptake. Visit pioneer.com for more information on SDS scouting tips and management options, or contact your local DuPont Pioneer agronomist or Pioneer sales professional.
Selection of tolerant varieties is the best defense against SDS and other soybean diseases. Additional SDS management practices include planting disease-prone fields last, improving field drainage, reducing compaction, maintaining field fertility, evaluating tillage systems and reducing other stressors.
“Every disease and pest cycles in intensity from year to year, and at some point, SDS returns,” says Schnebly. “When conditions are ripe for SDS, we want to have the best, tolerant products on the market—we can’t let our customers down.”
Demanding research timelines enforce the need to maintain a high-intensity research effort in developing soybean varieties with tolerance to SDS and other diseases. “Developing any new soybean product requires seven to nine years of research,” Schnebly says. “We can’t back away from testing products for SDS tolerance just because we haven’t seen it in a couple of drier years.”
Research testing for SDS in areas affected by the disease is a group effort by DuPont Pioneer soybean research stations located across the Corn Belt. To ensure a high level of accuracy, Pioneer researchers work with local growers to identify field areas with high incidence of Fusarium solani, the fungus that causes SDS.
“Some of our SDS testing has occurred at the same field site over several years,” Schnebly says. “In those years when conditions aren’t good for SDS at one site, there might be a high incidence at another. Maintaining a large number of SDS test sites allows us to continue evaluating breeding material for Pioneer research as the conditions for SDS vary year to year.”