Soybean sudden death syndrome (SDS) is widespread in Iowa. This year has had one of the worst epidemics since the disease was found in Iowa in 1994. Severely infested soybean fields can be found in every region in Iowa. It is easy to spot brown patches caused by SDS while you are driving the highways. Fields with large portions of premature defoliation can be found in early August.
The disease can be a big surprise to us. We had good planting, enjoyed wonderful soybeans in July and were expecting good yield; and some may have made marketing moves. Then SDS suddenly turns the fields brown with sick-looking plants in August. It struck us, in many ways, like white mold.
Many contribute this year’s SDS outbreaks to flooding. However, flooding is not 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. Spring and June conditions this year are the key to setting up this epidemic. Predictions made in February suggested that all parameters for this disease in the growing season were right for a widespread outbreak.
What can we do to minimize the disease this season?
There is nothing we can do about it with current measures. Everything we can do should have been done before or at planting.
Can we spray fungicide to reduce losses?
No. No chemical sprays are effective in controlling this disease. It is a waste of money.
What kind of yield losses can be expected?
The losses vary from field to field and area to area, depending at what growth stage the disease shows up and how large an area is affected. I have seen losses as high as 30 bu./acre in severely infected fields. Sometimes the losses are minimal if the disease shows up in later August. Generally severe premature defoliation can lead to 10-bu. losses.
What can we do now?
This year is a very good year to polish your SDS management skills, especially variety selection. Use local information for variety selection. Resistance information from other states, especially from field tests done in southern regions, has little use in Iowa and sometimes can be misleading, as this disease is very environmentally dependent. Look at the fields around your farm – healthy-looking, SDS-free soybeans in flat or lowland fields that were planted earlier. That field likely has a good variety for you.