A yield robbing soybean disease, Soybean Sudden Death Syndrome is widespread in Iowa fields this summer. In fact, this year has had one of the worst epidemics of SDS since the disease was found in Iowa in 1994. Severely infested soybean fields can be found in every region in Iowa—although central, eastern and southeast Iowa have it worst.
It is easy to spot the brown patches in green soybean fields caused by SDS while you are driving the highways. Fields with large portions of premature defoliation were being seen in early August.
"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 we were expecting a good yield. Then the disease suddenly turns areas of the fields brown with sick looking plants in August. It strikes us, in many ways, like white mold does."
May and June conditions helped set up SDS epidemic
This year’s flood reminds Yang of the 1993 flood, and many people are saying this year’s SDS outbreaks are due to flooding. However, flooding isn’t the reason for a major outbreak. "Remember, 2008 was a flood year with high prevalence of SDS, but the disease that year caused less damage than this year," notes Yang. "May and June conditions this year were the key to setting up this epidemic. Early predictions I made in February suggested that all factors for this disease in the upcoming 2010 growing season were right for a widespread outbreak."
Sudden Death Syndrome is a dramatically-named soybean disease that often slashes yields by 20% to 60%. The worst infestations in Iowa this year appear to be in central, eastern and southeast Iowa. The band of infestation extends on over into north central Illinois. A farmer near Peoria says this is the first case of SDS he’s ever witnessed in his area. Yang says Illinois, southern Minnesota and eastern Nebraska soybean fields are being affected to a lesser degree by SDS.
Whole fields this year are being hit hard by SDS outbreak
Although SDS is caused by a soil fungus that infects soybean roots early in the growing season, symptoms do not become apparent until July and August, first appearing as yellowish spots on the soybean leaves. All 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 condition, which results in premature death of soybean plants at the same time that the pods are in the critical filling stage.
"Losses will vary from field to field, depending at what growth-stage the disease shows up and how large of an area is affected in the field," says Yang. "I’ve seen losses as high as 30 bushels per acre. Generally, severe premature defoliation can lead to 10 bushel per acre losses."
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 on the market today exhibit complete resistance to SDS. The disease is also made worse by exceptionally early planting in wet soil, exactly the type of field conditions which prevailed across the Midwest last spring.
Questions and answers regarding SDS management
Looking ahead to next year and beyond, what can farmers do to better manage SDS? Yang provides the following answers to this often-asked question and related questions he’s been receiving.
* What can you do during the growing season to minimize this 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 2010 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 SCN.
* 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.
* 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 bushel per acre in severely infected fields. Sometimes the losses are minimal if the disease shows up in the later part of August. Generally, severe premature defoliation can lead to 10 bushel per acre losses.
* What can you do for 2011 and beyond? This is a very good year to polish your SDS management skills, especially soybean variety selection. Use local information when choosing soybean varieties to plant. SDS resistance information from other states, especially from field tests done in southern regions of the U.S., has little use in Iowa and sometimes can be misleading, as this disease is very environmentally dependent.
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.
Currently, there is lot of information on this disease--some good, some so-so and some of it is 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 will also present information at winter meetings on what to do for next year’s crop and future management of SDS.