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Soybeans - What happened in 2008?

November 14, 2008
By Wayne Schoper, Brown/Nicollet Extension Educator

The soybean harvest has been over for awhile and we have been hearing reports that show a lot of variability in yields. Some farmers have reported exceptional yields in the mid-50's and into the 60's. However, the main consensus says that overall, the soybean harvest was somewhat disappointing with a lot of reports that saw yields in the 40 to 50 bushel per acre range. Some of this can be attributed to the dry weather we saw in August. Many soybeans were planted late and hit the dry weather at the wrong time. Soybean aphids were also around this year, although most producers did spray for them at least once. We do know that most fields hold some level of Soybean Cyst Nematodes (SCN). However, symptoms of this disease, although present, were less obvious than in previous years. Bruce Potter, U of M IPM Specialist, has said that SCN may not have been as prevalent this year due to cooler growing conditions and a later planting date that may have limited the number of SCN generations.

So what else might have contributed to some of the lower yields that have been reported? A few weeks ago, I wrote a column on some of the late season diseases that had showed up in some area fields. Those diseases that we were seeing at that time included Sudden Death Syndrome (SDS) and Brown Stem Rot (BSR) as well as an old nemesis - White Mold. Although they were present, they did not appear to be a major player in limiting soybean yields.

Another suspect could possibly be Pod and Stem Blight. According to Bruce Potter, symptoms for this disease showed up earlier than usual this year. Late season symptoms were the highest that he had ever seen. If you had the opportunity to look at a few soybean stems this fall you might have noticed the distinctive black fruiting structures arranged in rows on the stems of the plants. Although this disease could be a suspect, a higher incidence of Pod and Stem Blight does not necessarily mean that this is the cause of lower yields. The presence of this disease may indicate that soybean stress allowed these symptoms to appear. There are a few soybean varieties out there that are resistant to this disease and they should show a better yield than non-resistant varieties.

So what does this all mean? Every growing season is different and 2008 was no exception. As we mentioned before, we did get a late start on soybean planting this year. Usually, at least in recent years, we have most of the corn planted by the first week in May. Soon after, the soybeans go into the ground and we are off and running with another growing season. In 2008, we had some corn planted in April and then we hit an extended period of rainy weather that pushed us back 7 to 10 days. This meant that many soybeans didn't get planted until the end of May and in some cases, into the month of June. This compressed the growing season somewhat, and coupled together with the dry weather in August and some of the aforementioned fungal diseases, worked together to limit yields. Will this have an effect on the 2009 growing season? Only time will tell. I doubt that we will ever be able to find a single cause to all of this. It appears that there are combinations of causes that may shift from year to year. My best advice is to select a good yielding soybean variety that fits well into your soil type and management style and not try to outguess what kind of growing season that we might have.



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