By SHELLY STRAUTZ-SPRINGBORN
Michigan Correspondent

EAST LANSING, Mich. — Symptoms of Sudden Death Syndrome (SDS) have been identified in soybean fields throughout much of the Midwest.

First documented in the late 1960s near the Mississippi River in Arkansas and Tennessee, SDS occurs primarily in Alabama, Delaware, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Missouri, Ohio, Texas and Wisconsin.

This year, the upper Midwest – Minnesota, Iowa, Illinois, Wisconsin, Nebraska, Missouri, South Dakota and Michigan – is especially affected. The disease is more widespread in Iowa, where growers report it is severely damaging their crop.

“This year’s yield losses to SDS are expected to exceed 20 percent in some fields,” said David Wright, Iowa Soybean Assoc. director of contract research.

“In north-central Iowa we are seeing widespread SDS for the first time,” said Dean Coleman, a soybean grower from Humboldt. “We have spots varying from small areas to more than two-thirds of fields.”

In Michigan, the disease has been popping up in fields in the southwestern and south-central regions of the state and is prevalent in southern Berrien, St. Joseph, Calhoun, Cass, Van Buren and Monroe counties, according to Keith Reinholt, field operations director with the Michigan Soybean Promotion Committee.

Reinholt said the disease can quickly become a yield-limiting factor in production.

“There is definitely yield loss in areas within fields,” he said. “It is not always widespread, but it is in pockets. The total loss depends on the acreage size of the pockets.”

Reinholt said Michigan State University researchers have documented higher average temperatures in the state for 14 of the 15 weeks of this year’s growing season, coupled with above-average precipitation in the spring. These conditions closely parallel weather conditions elsewhere in the Midwest where the disease is more prevalent.

“They are wondering if this weather, which is paralleling the weather conditions throughout the central Corn Belt, is why we are having more problems this year,” Reinholt said.

The cause of the disease is a soil fungus that is widespread throughout the Midwest. It infects the soybean root early in plant development. Later in the growing season, the pathogen rapidly kills the plant during pod set and pod filling.

SDS is characterized by leaf spots and root decay. As the name implies, plants that appear to be normal suddenly turn yellow and die rather quickly. The disease causes reductions in yield, which can range from slight losses to 100 percent, depending on the soybean variety.

Infection of the soybean root is worsened by cool weather as well as soil compaction and poor drainage.

MSU extension educator Bruce MacKellar said farmers should be on the lookout for areas of their fields that are exhibiting yellow- and brown-colored leaves in the upper plant canopy, that appear to be prematurely dying in the field. Plants will exhibit yellowing areas in the upper canopy, with severe symptoms showing browning tissue between leaf veins.

“Initial symptoms may appear as yellowish spots on the leaves. Highly infected plants will show excessive yellowing or premature leaf drop and relatively sudden plant death,” he said. “The primary damage from this disease is premature or aborted pod fill, which robs yield by preventing soybeans from sizing properly. How much yield loss occurs depends on how severely and how early the symptoms begin to develop in the field.”

MacKellar said scouting is necessary because not all yellowed pockets of soybean fields are caused by SDS. Other causes include manganese deficiency, potassium deficiency, spider mite damage and the lingering impacts of wet spots in fields.

New research suggests the critical stage for the SDS pathogen to infest soybean plants is before emergence of the germinated seed. The disease is caused by a soil-borne fungus that is primarily spread with the movement of soil from field to field on equipment, human and animal feet, birds and wind and water erosion.

There is no treatment for the disease; however, farm management decisions can help alleviate the disease pressure. Researchers offer several recommendations for SDS management.

Farmers should consider planting varieties of soybeans with the best tolerance to SDS in fields where the disease has been detected. Improving soil drainage by installing tile in slow-drying areas can help deter the disease, because excess water and soil compaction are key factors increasing the severity of it.

SDS is often more severe in areas also infested with soybean cyst nematode (SCN). Thus, researchers suggest growers also plant varieties with good resistance to SCN and test soils frequently to monitor nematode populations.