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SDS hits hard in 2010

A yield-robbing disease, soybean sudden death syndrome is widespread in Iowa this summer. Severely infested soybean fields can be seen to some extent in every region of the state in 2010. This year has had one of the worst epidemics of SDS since the disease was found in Iowa in 1994.

It is easy to spot brown patches in green soybean fields caused by SDS while you’re driving the highways. Fields with large portions of premature defoliation were already seen in early August in many areas of the state.

Key Points

• Soybean sudden death syndrome is widespread in Iowa this summer.

• This is one of the worst epidemics since SDS was first found in Iowa in 1994.

• Pay attention to soybean variety differences and their ability to resist SDS.

“This disease can be a big surprise to us,” says X.B. Yang, an Iowa State University Extension plant pathologist. “This year we made good progress in planting, enjoyed wonderful soybean growth in July and were expecting a good yield. Then the disease suddenly turned areas of fields brown with sick-looking plants in August. SDS strikes quickly, in many ways, like white mold does.”

This year’s flooding and wet growing season reminds Yang and his Iowa State University colleagues of the 1993 flood, and some people are saying this year’s SDS outbreaks are due to flooding. However, flooding is not the reason for a major outbreak, says Yang.

“Remember, 2008 was a flood year with high prevalence of SDS, but the disease that year caused much less damage than this year,” he explains. “May and June weather conditions this year were the keys to setting up the 2010 epidemic. Early predictions we made in February suggested that all parameters for this disease in the upcoming growing season were right for a widespread outbreak of SDS to occur.”

Confidently, Yang says, “Those farmers who followed my prediction and recommendation in March should end up with little loss to SDS this year.” His advice included variety selection. There are SDS-tolerant soybean varieties, which offer some but not complete resistance to the disease. For now, there is no truly SDS-resistant variety available for farmers to plant.

Still, you can do more than just select varieties with some resistance to SDS to minimize potential yield reduction from this disease, says Yang. In fields that have a history of SDS, you can wait to plant them last, when temperatures are warmer and soils are drier. Also, if you can tile your fields to improve drainage, that helps reduce SDS problems. Avoiding compaction and controlling soybean cyst nematode also help.

SDS questions and answers

Looking ahead to next year and beyond, what can farmers do to better manage SDS? Yang provides these answers to this and related questions.

What can you do during the growing season to minimize the disease? There is nothing you can do about it with current measures. Everything you can do should have been done before or at planting. In a March SDS prediction article authored by Yang and available online, he said the wet, cold spring could bring on SDS. Before planting, knowing if SDS is likely to strike is critical to managing it, especially when you have to also deal with white mold and soybean cyst nematode.

Can you spray a foliar fungicide to reduce losses from SDS? The answer is, “No.” There are no chemical sprays currently available that are effective in controlling this disease. It is a waste of money to try this management tactic.

What kind of yield losses can you expect? Losses vary from field to field and area to area, depending at what growth stage of the soybean plant the disease shows up and how large of an area is affected in a field. Losses have been as high as 30 bushels per acre in severely infected fields. Sometimes the losses are minimal if the disease shows up in the latter part of August. Generally, severe premature defoliation can lead to 10-bushel-per-acre losses, or more. 

What can you do for 2011 and beyond? This is a good year to polish SDS management skills, especially soybean variety selection. Use local information when choosing soybean varieties to plant. Soybean variety resistance information from other states, especially from field tests done in the South, has little use in Iowa and sometimes can be misleading, as this disease is very dependent on environmental factors.

Look at fields around your farm and identify the healthy-looking SDS-free soybeans growing in flat or lowland fields that were planted earlier than other fields this past spring. That healthy-looking field likely has a good variety growing in it. Good corn harvesting in the fall also helps reduce SDS risk. Studies by Yang and his colleagues recently found that corn kernels left from harvest increase SDS fungus. Kernels on the ground after harvest are an excellent food source for this fungus.

A lot of information is available on this disease — some good, some so-so and some misleading. After this season and after evaluating the results of this year’s studies, Yang will write an article in ISU’s ICM Newsletter and present information at winter meetings on what to do for next year’s crop and future management of SDS.

What causes sudden death syndrome?

Although soybean sudden death syndrome is caused by a soil fungus that infects soybean roots early in the growing season, symptoms don’t become apparent until July and August, first appearing as yellowish spots on the bean leaves. Infected leaves eventually whither and die, killing the plant.

Unlike some years, when SDS is limited to small areas within a field, whole fields in 2010 are being affected by the disease, which results in premature death of soybean plants at the same time the pods are in the critical filling stage.

Farmers with fields infected by SDS have little recourse, apart from rotating to a different crop, as no fungicides exist to battle this disease and no soybean varieties available today exhibit complete resistance to SDS. The disease is also made exceptionally worse by early planting in wet, cool soil, exactly the field conditions that prevailed across the Midwest this spring.


disease widespread: Sudden death syndrome is widespread in Iowa this year. This flooded soybean field in Polk County with severe SDS infestation shows large areas of bean plants dying in early August.

This article published in the September, 2010 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.