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Research Highlights

Research Highlights
SCN, Frogeye cause yield loss, board funds research to investigate

By Kentucky Soybean Board

The 2017 Yield Loss Disease Estimates are in, and it’s safe to say that Soybean Cyst Nematode and Frogeye Leaf Spot, followed by seedling diseases (due to Fusarium, Pythium, Phomopsis, and Rhizoctonia), Stem Canker, Pytophthora Root and Stem Rot, Septoria Brown Spot and Sudden Death Syndrome are taking a toll on yields here in Kentucky. A big toll.

The aforementioned diseases combined are estimated to have cost Kentucky soybean farmers 6,743,084 bushels in 2017 alone.  In the Southern states, Soybean Cyst Nematode is the number one yield-robbing disease, while Frogeye Leaf Spot holds the number three spot. Kentucky experiences minimal yield loss from the number two-ranked disease, Root-Knot Nematode.

Across the United States, yield loss from disease is estimated to be 440 million bushels for 2017, and University of Kentucky Extension Plant Pathologist Dr. Carl Bradley intends to identify, monitor and suggest management options for key diseases and pathogens here in our state.

Bradley has just wrapped up a two-year project, funded by the Kentucky Soybean Board, that focused specifically on Frogeye Leaf Spot in Kentucky. He worked in collaboration with Dr. Claire Venard, who conducts the UK Soybean Variety Trials in eight lo-cations across the state (also funded by the Kentucky Soybean Board), to research the varieties that are susceptible and resistant to Frogeye Leaf Spot and the efficacy of various fungicides.

Bradley said that he appreciates the Board’s funding, and that it’s important to him that he convey his projects’ findings to the producers who will benefit from his research. He’s currently working on a fungicide response database, which will be used for extension presentations and newsletter articles.

In his newest project, titled “Management of Important Dis-eases and Pathogens That Affect Kentucky Soybean Production,” Bradley intends to focus on field research designed to evaluate different practices for management of significant soybean diseases across Kentucky. This project was funded at the March Board meeting and will focus on Frogeye leaf spot, southern stem canker, target spot, Phytophthora root rot, and soybean cyst nematode. Treatments evaluated will include foliar fungicides applied at different timings, nematicide seed treatments, and different soybean varieties.

“Many farmers here in Kentucky are planting Soybean Cyst Nematode resistant varieties,” Bradley said, “but SCN has adapted and is still causing yield loss, even in resistant varieties. Unfortunately, one of the practices that makes SCN worse is back-to-back soybean crops with no corn rotation in between. Frogeye Leaf Spot, our number two disease, also increases in a soy-be an- on- soybean situation.”

Since the economics make sense for soybean-on-soy-bean plantings right now, many farmers are opting out of the corn rotation, and others are declining to plant wheat for double-crop purposes.

Fungicide resistance is also a problem, Bradley said. Building on the Frogeye Leaf Spot project from 2016 and 2017, Bradley said that strobilurin fungicide-resistant strains have made Frogeye Leaf Spot a more difficult disease to manage. Re-search has shown that a combination of resistant varieties and effective foliar fungicides can allow complete management of frogeye leaf spot, but more research is needed to better understand which products and at what application timing will provide the greatest control of this disease.

Soybean Cyst Nematode is more complicated, Bradley says, because we don’t have as many options to control it. Also, since SCN doesn’t show symptoms on the foliage, it’s often an undetected pathogen. Seed treatments called nematicides will be tested to see what’s working.

Bradley was excited to share that a new Soybean Cyst Nematode Coalition has been formed to help the agricultural industry speak with one voice about SCN management. The coalition was started by the North Central Soybean Research Program and is supported by the United Soybean Board. Coalition members include personnel from 27 universities and industry partners BASF, Bayer, Growmark, Monsanto, DuPont Pioneer, Syngenta and Winfield United. “The Coalition is working to bring back the message that SCN is a big yield reducer,” Bradley said. “We have to let people know that it’s able to overcome resistant varieties.”

He added that there are new things in the pipeline to work against SCN, including new seed treatments. It’s important, Bradley said, to test your fields. The first SCN Coalition formed in 1997, after a survey of 1,325 soybean farmers showed that 65 percent of them had never tested fields for SCN.

The difference this time: SCN is adapting and reproducing on SCN-resistant soybean varieties – and yields are decreasing. Managing SCN is becoming more complicated than planting a resistant variety, explains Bradley. Thanks to the Coalition and a new national campaign on SCN, Bradley says that farmers will be hearing more about this yield-robber. “There should be information in ag mags going forward, and I think extension personnel will be talking more about SCN in the coming months. The thing is, if a field has SCN, you won’t be able to get rid of it, but you can manage it.”

United Soybean Board Vice President Keith Tapp of Sebree, Kentucky, said that he is glad to see the Coalition taking action. “USB has been investing heavily in the fight against soybean cyst nematode in the past few years. The checkoff investment in SCN has been more than $7.8 million over the past five years – that includes USB and state soybean boards – so I think it’s clear that the farmer-leaders are taking this issue seriously and putting forth funds to combat it.”

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.