Soybean Sudden Death Syndrome spreading fast
Janet Kubat Willette
Date Modified: 12/01/2009 11:37 AM
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Agri News staff writer
WASECA, Minn. -- Soybean Sudden Death Syndrome has spread to 23 counties in Minnesota since it was first confirmed in the state in 2004.
"This is important because it's spreading rapidly across the state," said Jim Kurle, a University of Minnesota soybean disease specialist.
Kurle spoke at the June 23 Agronomy Field Tour at Southern Research and Outreach Center in Waseca. About 125 people attended the field tour.
The pathogen that causes Sudden Death Syndrome starts with a root infection, but foliar symptoms aren't visible until later in the growing season, usually stage R5 or R6, which occurs in mid- to late August just before soybean maturity, Kurle said.
Ideal growing conditions, especially in August, result in the most severe symptoms, he said.
Sudden Death Syndrome is seen in low, poorly drained areas of fields. It occurs in headlands where there's compaction and in traffic areas where farmers drive across fields. It's found in fields with subsoil conditions that interfere with drainage.
Brown Stem Rot has similar foliar symptoms to SDS and they develop about the same time. The difference is with Brown Stem Rot, the pith turns brown. The pith retains its normal color when the soybean is infected with SDS.
Foliar symptoms with SDS can progress to loss of leaflets and interveinal chlorosis, but the symptoms don't always progress that way, Kurle said.
The severity of SDS isn't reduced with the rotation to just about any other crop grown in Minnesota and SDS effects other crops, especially other legumes, he said. Brown Stem Rot, on the other hand, is reduced in severity with rotation because the disease is harbored in the soybean residue. It's not clear where the inoculum persists with SDS, Kurle said.
This year appeared to be a variable year for SDS, he said. Kurle doesn't think it was as widespread as in other years, but in some areas it was severe.
Kurle is studying SDS in the greenhouse right now. Plants are inoculated for SDS and studied. The recent bright sunlight has resulted in nice foliar symptoms in the infected greenhouse plants. Cloudy weather tends to produce inconsistent results, he said.
He's looking for varieties suited to Minnesota that might be more resistant to SDS. He's also looking for more effective ways to inoculate plants. The U of M is also collaborating with the North Central Soybean Research Program to try to explain why inoculation techniques are not performing consistently.
There are soybean varieties that are partially resistant to SDS, but if the environment is conducive the disease may still appear. Up until now, Kurle hasn't run across any effective seed treatments.
There also appears to be a relationship, albeit not a well understood one, between SDS and Soybean Cyst Nematode. It seems to be pretty consistent that the two are found together.
SDS seems to be more severe where SCN is present, however when SCN is controlled data from other states is not as consistent on the effect on SDS.
Kurle recommends that farmers manage SCN as part of their SDS management even though the results are inconsistent. Different problems taken together will add up to reduced yield, he said, and dealing with SCN is the appropriate thing to do.
Farmers should look at resistant soybean varieties that are appropriate for the area they are growing soybeans in. If they have both SDS and SCN, they should look for varieties in their desired maturity that have resistance to both.
The greenhouse soybeans get SDS without SCN and they show early symptoms, three to four weeks after germination, Kurle said. The north central states use that system for initial tests of germplasm and varieties.
Formerly, Minnesota soybean varieties were sent to states like Illinois and Indiana for SDS testing. The problem is that varieties behave differently there because of the longer day length and longer growing season. Varieties are adapted to a narrow range, he said.
SDS has been a problem in Illinois and Indiana since the early 1990s, so those states have more experience with it. In Illinois, SDS got to be so severe that farmers were counseled to plant soybeans later into warmer and drier soils. However, they paid a yield penalty for later planting, Kurle said.
One reason there may be more problems with SDS, SCN and BSR is that soybeans are a relatively new crop in Minnesota. Soybeans became a common crop in the 1970s, he said, and now its production has intensified. In the past, there were four to five crops in a cropping rotation. Now, the cropping rotation has been shortened to two crops for most people.
Kurle speculates that two-crop rotation has a relationship to more disease problems with soybeans. A longer rotation may deal with BSR and SCN more effectively.