Seeing yellow spots in your soybeans?

Seeing yellow spots in your soybeans?

Yellow areas in soybean fields are showing up; it could be the start of SDS or other diseases.

Are you seeing yellowish spots showing up in your soybean fields, especially in compacted parts of the field? This could be the start of Sudden Death Syndrome (SDS). "With how wet it's been this year in much of Iowa, we've had ideal conditions for disease development," observes Rebecca Ahlers, Iowa State University Extension field agronomist in southeast/south-central Iowa.  

BEAN DISEASES: Are you seeing patches of yellowish soybean plants showing up in bean fields, especially in compacted parts of the field? It could be the start of sudden death syndrome (SDS). With a wet growing season, most of Iowa has had ideal conditions for disease development.

"I've been in a few fields were you can start to see SDS symptoms appearing," she says. "I'm mainly seeing it in early planted soybean fields so far. Infected plants will have yellow spots between leaf veins early on. As the disease develops the spots will grow and form large chlorotic and necrotic blotches between leaf veins. The leaf will remain green around the mid-vein and major lateral veins."

Don't confuse SDS symptoms with other bean diseases
You need to be careful though because the foliar symptoms of SDS also look similar to the foliar symptoms you may see with brown stem rot, or BSR, she adds. "To be sure which disease you are seeing, split the stem. If the pith is white, then it is likely you have SDS. If the pith is brown, then you have BSR. You can also check the roots. Plants with SDS will have root rot where as BSR does not cause root rot."

Unfortunately there is nothing you can do for SDS now, but you can start thinking about what to do to help in the future, notes Ahlers. "Talk with your seed dealer about soybean variety selection and even what seed treatment options are available," she advises. "Planting date might be another factor as SDS is mostly showing up in the earliest planted soybeans. Soil compaction is another big item; elevating compaction may help decrease the severity of SDS."

ISU Extension plant pathologist Daren Mueller and Tristan Mueller, Iowa Soybean Association On-Farm Network manager of agronomic research, published an ISU ICM newsletter article a few weeks ago that discuss soybean diseases that are showing up this year. Other diseases that Ahlers has seen in southeast and south-central Iowa (in isolated areas) include frogeye leaf spot, bacterial blight, and septoria brown spot, as well as some viruses. 

Wet conditions, cool temperatures early, favor SDS development
Wet conditions and cool temperatures early-on in the growing season set up the season for SDS development. The disease typically doesn't show symptoms until after the early reproductive stages of the soybean plant. The pathogen that causes SDS infects the roots and sends a toxin up the plant that causes the yellowing and dead tissue between veins, says Daren Mueller.

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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 the ground because of root damage.

Seeing yellow spots in your soybeans?

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So what can be done to control SDS? Numerous research entities are trying to figure that out. They include the Iowa Soybean Association's On-Farm Network, the USDA North Central Soybean Research Program and Iowa State University.

Seeing yellow spots in your soybeans?

SDS SYMPTOMS: Early signs of sudden death syndrome, like these yellow lesions, are showing up in some fields in Iowa this August. 

How can you reduce the risk of SDS attacking soybeans?
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 suggests 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, which is 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," says ISU's Daren Mueller. "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."

New seed treatment ILeVO is being tried by farmers this year
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 and a number of farmers are trying it this year.

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This year the On-Farm Network in a collaborative project with ISU and Bayer Crop- Science is testing the fungicide seed treatment ILeVO, through its replicated strip trial process. With this being the first year ILeVO is on the market, it is important for research groups such as the On-Farm Network to allow farmers the opportunity to experience this product firsthand while simultaneously determining the efficacy of SDS control, says ISA's Tristan Mueller.

ILeVO controls SDS pathogen, and may also protect against SDS
In addition to controlling the SDS pathogen, ILeVO could also show 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 ISA's "Advance" newsletter which is available online to ISA members.

Seeing yellow spots in your soybeans?

BROWN STEM ROT: To be sure which disease you are seeing in a field, split the stem. If the pith or inside of the soybean stem is white, then it is likely you have SDS. If the pith is brown, then you have BSR.

"This project is a great example of ISA, ISU and industry working collaboratively," says ISA's Tristan Mueller. "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, ILeVO, as well as the funding for this study."

Farmers who have set up their own trials testing ILeVO or other products are encouraged to work with their ISA 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 800-383-1423 or visit safarmnet.com.

TAGS: USDA Extension
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