Wet conditions and cool temperatures early on set up the season for SDS development. The disease typically does not show symptoms until after the early reproductive stages. There are several clues to watch out for while scouting for SDS. The symptoms first appear as yellow between leaf veins. These may look similar to the symptoms of brown stem rot (BSR), but can be distinguished by splitting the plant’s stems. If the inner-stem is white, the field most likely has SDS. The pathogen that causes SDS infects the roots and sends a toxin up the plant that causes the yellowing and dead tissue between veins.
As the disease progresses the yellow and brown areas become large irregular shaped lesions, still staying between the veins. Another symptom of SDS is rotted roots. An infected plant can often be easily pulled from ground because of root damage.
So what can be done to control SDS? Numerous research entities are trying to figure that out. Among them are the Iowa Soybean Association (ISA) On-Farm Network, the North Central Soybean Research Program (NCSRP) and Iowa State University.
While there is no in-season control of SDS, there is research being done on ways to reduce the risk of SDS on soybeans. Prevention research includes tillage, improving soil health, crop rotation and planting date. While these continue to be tested, data suggest that while certain tillage practices and improved soil health may incrementally reduce SDS risk, crop rotation actually increases the likelihood of the disease becoming an issue. This is because corn, soybean’s primary rotational crop in Iowa, while it shows no foliar symptoms of SDS, is still a host for the disease.
“While there is some evidence that changing planting dates or tillage practices may have an effect on SDS control, we don’t recommend farmers change these practices solely for this reason,” said Daren Mueller, ISU Plant Pathology assistant professor. “Farmers should use the most effective tillage practices and planting dates for their entire operation, not in an attempt to control one disease because of all the factors involved.”
Until recently, the primary option for farmers wanting to control SDS was varietal resistance. While this is still the best option, more protection is sometimes needed. This year a new fungicide seed treatment that has the potential to protect against SDS entered the market.
This year the On-Farm Network in a collaborative project with Iowa State University and Bayer CropScience is testing the fungicide, ILeVO, through its replicated strip trial process. With this being the first year ILeVO is on the market it is important for research groups like the On- Farm Network to allow farmers the opportunity to experience this product firsthand while simultaneously determining the efficacy of SDS control.
In addition to controlling the SDS pathogen, ILeVO could also shown potential in protecting against soybean cyst nematode (SCN). Along with scouting for disease ratings the On-Farm Network and ISU are taking stand counts and soil samples to determine how effective ILeVO is against SCN. All these observations and results will be made available in early-September editions of the Advance and in the On-Farm Network’s replicated strip trial database after the season.
“This project is a great example of ISA, ISU and industry working collaboratively,” said Tristan Mueller, ISA On- Farm Network operations manager of agronomic research. “ISA is contributing funding and our replicated strip trial data, ISU is collecting and processing samples as well as bringing additional scientific rigor to the project and Bayer CropScience provided the seed treatment as well as funding for this study.”
Farmers who have set up their own trials testing ILeVO or other products are encouraged to work with their regional field research specialist to get their data processed and analyzed. In order to collect imagery for the new fields, data should be submitted by August 15. For more information or to learn how to submit data call 1-800-383-1423 or visit isafarmnet.com.