A fatal soybean disease is again infecting the Indiana crop, and Purdue University researchers are monitoring its spread and potential damage.

Sudden death syndrome (SDS), a soilborne fungus that attacks a soybean's root system, has turned up in soybean fields in southwest, north-central and northwest Indiana. Other areas of the state also may be susceptible.

Scott Abney, a USDA professor in Purdue's botany and plant pathology department who specializes in soybean diseases, said it is too early to predict crop losses stemming from SDS. Abney spoke today (Thursday, 8/24) at an SDS informational meeting in Knox County.

"There are indications that SDS is worse this year than it was last year," Abney said. "What happens in the next week and a half will dictate losses."

Indiana is projected to produce a record 260.3 million bushels of soybeans this fall, according to an Aug. 10 outlook report by the Indiana Agricultural Statistics Service. 

The SDS outbreak is occurring later this year, Abney said. Soybean plants may be far enough along in infected areas of Indiana to yield some crop even if the plant dies, he said.

Currently, there are no soybean varieties that are highly resistant to SDS. However, Abney said farmers can reduce the affects of SDS by selectively choosing soybean varieties that perform better in severe SDS years; diversifying or choosing varieties of more than one maturity classification; increasing crop rotation times; and planting soybeans later in May.

"It's also important to maintain plant health through management practices that reduce competition from weeds, damage from insects or other diseases, and stress from soil compaction or other soil factors," Abney said.

SDS is a root-rot disease that gets its name from the sudden appearance of small yellowish blotches on soybean leaves. It was first identified in Arkansas in 1971 and showed up in Indiana soybeans in 1985. SDS did significant damage to the Indiana soybean crop in 1993 and 1998.

While referred to as a "sudden" disease, SDS is actually a slow-developing infection. The fungus Fusarium solani f. sp. glycines enters the soybean plant early in the season but usually manifests itself later as the plant nears maturity. 

Leaf discoloration is caused by toxins produced by the SDS fungus. The blotches grow larger in size and number and the tissue within the infected area becomes brown and dies. As the disease progresses, entire plants may become infected. The discolored leaves may fall off, leaving barren petioles attached to the stems.

SDS thrives in wet conditions during soybean pod and seed development. The heavy rains that drenched much of Indiana earlier this month have contributed to the SDS outbreak, Abney said.

Knox County was among the first counties to be hit with SDS this year. Jerry Nelson, a Purdue Cooperative Extension Service educator in Knox County, said he's seen evidence of SDS in many soybean fields.

"One field may have an infected plant here or there and another field may have a third of its plants infected," Nelson said. "A fertilizer dealer told me that 80 percent of his customers have SDS in at least some of their fields."

Nelson said he's received numerous SDS-related calls from farmers. Concern was so great Nelson arranged today's informational meeting.

The Knox County educator said SDS has spread into surrounding counties, including Daviess, Gibson, Sullivan and Vigo.

About 125 miles northeast in White County, Extension educator Greg Bossaer said soybean farmers are witnessing the first stages of SDS.

"It's frustrating to producers to look out there on the first of August and see a pretty promising soybean crop, and then see this," Bossaer said.

SDS symptoms could pop up in eastern Indiana soybean fields in the weeks ahead. Many eastern fields were planted later than those in western Indiana, Abney said.

Abney's SDS research is partly funded by the Indiana Soybean Board.

Sources: Scott Abney, (765) 494-9859, tsabney@purdue.edu 

Jerry Nelson, (812) 882-3509, jerry.nelson@ces.purdue.edu 

Writer: Steve Leer, (765) 494-8415, sleer@aes.purdue.edu 

Other source: Greg Bossaer, (219) 984-5115, gregory.bossaer@ces.purdue.edu 

Purdue news release
N2956