ANKENY, Iowa – This spring’s cool, wet weather is making it difficult for farmers to plant their soybeans and making it easier for a well-known pest to affect this year’s crop.
Sudden death syndrome (SDS), a soil-borne fungus, is a disease that is highly dependent on the weather and the resistance level of the planted soybean varieties. Dr. Leonor Leandro, Iowa State University assistant professor of plant pathology, said conditions favoring SDS include compacted soil, soil with poor drainage and interaction with the soybean cyst nematode. Fields with a history of SDS are also more at risk.
Leandro said years with abundant rainfall throughout the season are most favorable for SDS.
“This year, we’ve had a particularly cool spring, and planting has occurred later than usual,” she said.
The unknown factor now is how wet the remaining season will be. If the current prediction is correct and the summer is dry, the risk of SDS will be low. But if soybean plants get into the reproductive stages and good rainfalls occur, Leandro said SDS might show up. She said yield losses vary greatly, depending on the weather in a given year or location.
“Up to 100 percent yield losses have been reported in particular fields or sections of the fields. This especially occurs when the disease shows up in early reproduction stages. In 2010, Iowa experienced a very widespread, severe epidemic, and that year, the loss was estimated about 28 million bushels. In 2011 and 2012, the losses were very little because the summers were so dry.”
Leandro said the important thing for growers to note is that while the weather each year cannot be predicted, measures can be taken to reduce the effect of SDS if it appears. The most important measure is to plant SDS-resistant soybean varieties.
“There is no complete resistance to SDS, so any variety will develop some disease if it is in very favorable conditions, but they are going to suffer less yield loss than the more susceptible varieties,” she said. “Many of the varieties that are resistant to SDS are also resistant to the soybean cyst nematode. Growers should try to select varieties that have resistance to both because there is an interaction with the soybean cyst nematode and SDS. If you manage both at the same time, you are going to be more effective at reducing losses from SDS.”
In addition to using resistant varieties, Leandro suggested growers use an integrated approach of other disease management practices to minimize yield losses. For SDS, that would include reducing soil compaction, avoiding planting in cool, wet soil and improving drainage.”
To learn more, go to the Iowa Soybean Association website at www.iasoybeans.com/productionresearch and click on the podcast “Protect Soybeans from SDS Unknowns.”