Sudden death syndrome, a lethal soybean disease, has infected Iowa soybean fields this summer and is quickly robbing producers of profit potential.
The disease is not new to Iowa, but this year it is expanding into areas of the state and is showing up in fields where it has never been seen before. It often can be found in early planted soybean fields, but this year it seems to be appearing in fields planted through late May, according to Iowa State University Extension soybean agronomist Palle Pedersen. Pedersen talked about SDS and other topics at the ISU exhibit at the Farm Progress Show last week at Boone.
SDS tends to be most severe on well-managed soybeans with high yield potential. It can also be found in fields known to be infested with soybean cyst nematode and is generally more severe in those fields. Recent checkoff funded research has shown that SCN cysts can carry the SDS pathogen.
SCN cysts can carry SDS pathogen
Sudden death syndrome is caused by a fungal pathogen that enters the root within four days of germination. It is believed the pathogen remains in the root and crown area until the soybean plant enters the reproductive stage when it releases a toxin that moves throughout the plant, quickly killing the leaf tissue.
Foliar symptoms of SDS are easy to identify, but can be confused with those of iron deficiency chlorosis and brown stem rot. Look for yellowing of the leaf tissue between the veins followed by death of the yellow tissue. The only sure way to diagnose the disease and differentiate it from BSR is to split the stem lengthwise, says Pedersen.
Plants infected with SDS will show browning of the outer vascular stem tissue and will show signs of root rot; in contrast BSR infects and browns the inner vascular tissue and shows no root rot. SDS infections that occur early can result in pod abortion, reduced seed number and seed size. Infections that occur after flowering will not have a significant impact on yield.
Best way to manage SDS is variety choice
"The best way to manage this disease is to choose varieties with greater genetic resistance," says David Wright, director of contract research and strategic initiatives for the Iowa Soybean Association. "It is import for soybean producers and crop advisors to be able to accurately diagnose this disease. You must know what disease you are dealing with before you can effectively manage it."
Management options include planting varieties highly resistant to SCN and with greater resistance to SDS. The disease cannot be managed with fungicides. Wright says soybean farmers should scout their fields this year to identify which soybean varieties are more impacted by SDS. Rotate away from those varieties, and their sister varieties, next year, he advises.
Looking at different management practices
"We're looking at the possibility of reducing yield losses from SDS by improving our current management practices," says Pedersen. He's referring to ongoing research on farmers' fields that is funded by the Iowa soybean checkoff. "It is too early to tell right now," says Pedersen, regarding which management practices ISU will advise for control of SDS. "But we should know for sure in a year or two."
There are decision aids available that will enable farmers and other people who use them to accurately diagnose SDS and other yield-robbing pathogens. ISU and the Iowa Soybean Association recently released the Soybean Disease & Pest Management Field Guide. A handy spiral booklet that's not too big to carry in your pocket, it has high resolution color images and disease descriptions to help the user accurately identify most soybean diseases and insects.
Order your free copy by logging on to the ISU Extension publications store Web site at www.extension.iastate.edu/store or by calling the ISU Distribution Center at 515-294-5247 or calling the Iowa Soybean Association at 800-383-1423.