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Sudden death syndrome pops up in Iowa

Agriculture.com Staff 08/29/2008 @ 12:26pm

Sudden death syndrome (SDS) has infected Iowa soybean fields and is quickly robbing producers of profit potential, according to a report from the Iowa Soybean Association (ISA).

SDS, though not a new pest to Iowa, is expanding into areas where it has never been seen before. This year it seems to be appearing in fields planted through late May, crop-watchers say. The disease 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 the soybean cyst nematode (SCN); research has shown that SCN cysts can carry the 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 (BSR). 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.

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.

"The best way to manage this disease is to choose varieties with greater genetic resistance," says ISA research director David Wright. "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. Soybean producers should scout their fields to identify which soybean varieties are more impacted by SDS. Rotate away from those varieties, and their sister varieties, next year.

"We're looking at the possibility of reducing yield losses from SDS by improving our current management practices," says Palle Pedersen, Iowa State University Extension soybean agronomist. "It is too early to tell right now, but we should know for sure in a year or two."

Sudden death syndrome (SDS) has infected Iowa soybean fields and is quickly robbing producers of profit potential, according to a report from the Iowa Soybean Association (ISA).

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