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September 2, 2014

SDS and Cloudy Weather Potential Impact on Soybean Production

The weather continues to be beneficial for the soybeans and an argument could made for somewhat higher soybean yields based on the good weather. On the other hand, an argument could be made for somewhat lower soybean yields based on the amount of Sudden Death Syndrome being reported around the country and the persistent cloudy and wet weather we have had over the last several weeks.

Potential Impact of Sudden Death Syndrome on Soybean Production

There has been a lot of talk recently about Sudden Death Syndrome (SDS) is in the U.S. soybean fields. SDS is a soil borne fungus that can attack soybeans under the right climatic conditions and the disease appears to be most active during wet and cloudy periods. The disease causes the leaves to turn yellow and drop prematurely from the plant. The amount of damage caused by SDS can vary from slight to severe depending on the soybean variety and the stage of maturity of the soybeans when the disease appeared and how widespread the disease is in a specific field.

There have been numerous reports of SDS in Missouri, Iowa, Illinois, and Minnesota. There could well be more SDS than normal this year in specific locations, but I am not so sure that we can say at this point that there is more SDS than normal on a nationwide basis.

If SDS moves into a soybean field, it does not necessarily mean there will be a catastrophe. If the disease moves in late in the growing season and the leaves drop prematurely then what happens is that some of the developing pods at the top of the plant don't fully develop and the seeds in the other pods may not get quite as "plump" as they normally would. The soybeans still produce a crop, it just might not be quite as large as it would have been without the disease. If the disease appears early in the growing season, which is not the case this year, than losses can be greater.

In many of the fields where SDS has been reported the soybeans were only 2-3 weeks away from starting to mature normally. Therefore, the amount of losses caused by the disease will probably be somewhat limited. Additionally, improvements in the soybeans in other regions of the country could compensate for some of the losses caused by SDS.

Potential Impact of Cloudy Weather on Soybean Production

In addition to SDS, there is also a concern that the wet and cloudy conditions over the last several weeks could be somewhat of a problem for the soybeans. A lack of sunshine during the pod filling period can result in soybean yields that are not quite as good as expected. Under these conditions, the soybean plant expends a lot of energy producing a big and robust plant with a lot of vegetative material instead of putting its energy into producing pods and seeds.

This is a common problem in central Brazil where the peak of the rainy season (generally in January) can correspond to the peak of the pod filling period as well. The lack of sunshine during this period can result in somewhat disappointing soybean yields.

I think the combination of SDS, other diseases, cloudy weather, and excessive vegetative growth, will keep somewhat of a lid on potential increases in the soybean yield. Could it actually lower the nationwide soybean yield – that is probably yet to be determined. I look at it this way, those farmers expecting exceptionally high soybean yields might end up being a little disappointed.