For a disease to strike, certain environmental and soil conditions must align. The challenge, as you well know, is preparing for the unknown months in advance. The good news is knowing your risks for soybean cyst nematode (SCN), sudden death syndrome (SDS) and white mold, for example, can help determine your plan of attack. Farm Journal Field Agronomists Ken Ferrie and Missy Bauer, as part of the Farm Journal Test Plots program, have been studying how genetics, various seed and foliar treatments and population fit into a soybean disease management strategy.
How Genetics and Seed Treatments Fit Into the Plan
In the first of a two-year effort, Bauer set up field tests to determine if yield and return on investment can benefit by selecting soybean varieties with SCN resistance and seed treatments.
“Today we have more tools in the toolbox; we just need to determine the best ones for our farms,” Bauer says.
In south-central Michigan, field trials were conducted in three locations using two varieties (2.8 relative maturity) with genetic resistance for SCN: PI88788 has resistance to SCN races 14 and 3 and Peking has resistance to SCN races 1, 14, 3 and 5. Three seed treatment systems were evaluated on each variety as well: Bayer’s ILeVO plus fungicide and insecticide, fungicide and insecticide only and no treatment. Overall, the fields had low SCN pressure and no visual SDS symptoms.
Based on harvest results for the PI88788 variety, the best treatment was the ILeVO plus fungicide and insecticide, which increased yields 4.36 bu. per acre with a net gain of $17.75 per acre compared with the check. The fungicide and insecticide only seed treatment increased yields 1.83 bu. per acre with a net return of $4.95 per acre. (Therefore the ILeVO portion of the treatment yielded 2.53 bu. per acre more, resulting in a net return of $12.80 per acre.)
Coupled with the Peking variety, the ILeVO plus fungicide and insecticide treatment increased yields 3 bu. per acre, which resulted in a $4.45 net gain. The fungicide and insecticide only seed treatment increased yields 2.18 bu. per acre with net returns of $8.40 per acre compared with the check. (As a result, the ILeVO portion yielded less than a bushel per acre, which was not economical.)
“Since the Peking genetics have a stronger line of resistance it might be providing a lower response to the ILeVO seed treatment,” Bauer says.
When averaging the two varieties together, the best treatment was still the ILeVO plus fungicide and insecticide with a yield increase of 3.68 bu. per acre versus the non-treated check and a net return of $11.10 per acre.
In terms of SCN management, using the Peking genetic resistance and/or ILeVO did reduce SCN numbers based on soil samples at harvest. Stand counts improved with the fungicide and insecticide seed treatment.
“Imagery showed the ILeVO seed treatment typically resulted in a stay-green effect later in the season, which can increase yields if it helps improve seed size,” Bauer explains. “In 2017, August was very dry, which might have reduced typical yield gains from a stay-green effect.”
Even with relatively low SCN pressure and no visual SDS symptoms, ILeVO paired with a fungicide and insecticide seed treatment are good tools to improve yields in PI88788 genetics, Bauer says.
“This plot effort was also a good reminder of the importance of fungicide and insecticide seed treatments to increasing yields with good return on investment,” she adds.
In 2017, Bauer also gathered a third year of results on side-by-side trials comparing ILeVO plus fungicide and insecticide and a fungicide and insecticide only. Across multiple locations in 2015, 2016 and 2017, the ILeVO plots averaged a 3-bu.-per-acre increase. The benefit was most prominent in 2016 at 4.2 bu. per acre. In terms of economics, using ILeVO resulted in a $14.72-per-acre net return averaged for all three seasons compared with a fungicide and insecticide only. In 2016, ILeVO resulted in a $27.50-per-acre net increase.
In Illinois, the benefits of ILeVO varied based on planting date, field conditions and the weather.
“We’ve known for a while early planted soybeans produce optimum yields, but there are inherent risks such as decreased emergence because of cooler, wetter conditions; frost, which a soybean plant can’t bounce back from like corn; and the SDS window,” says Isaac Ferrie, who works with the Farm Journal Test Plots. “Seed treatments can lessen some of those risks by improving emergence when conditions are cool. The faster you get soybeans out of the ground and growing, the higher the likelihood of avoiding SDS.”
Based on planting date, the test plots in Illinois saw some yield bump using ILeVO in earlier soybeans in conventional-till conditions, but the benefit dwindled and was even negative the further into the planting window, Ferrie explains. The response lasted longer in no-till.
The biggest response to ILeVO in the same field in 2016 was a 19-bu. difference between treated and untreated strips. The average across all test plots was 5 bu. per acre.
In 2017, the ILeVO plots in Illinois didn’t result in a yield advantage. As Bauer saw in Michigan, using ILeVO can push back maturity.
“We could see that the soybeans stayed green longer, but that didn’t work in favor of yields at harvest, likely because August turned dry,” Ferrie says.
Big-Picture Approach to White Mold Management
White mold infection occurs during flowering, and wet, humid conditions increase the likelihood of an outbreak. In 2017, Bauer studied six different treatments to determine if variable-rate planting, a herbicide and/or fungicides are viable options to managing white mold, which includes reducing the occurrence, and if/how they impact individual plant yield components and overall yield.
“In the past, we’ve looked at a single component to control white mold. In keeping with the systems approach, we decided to broaden our efforts and study how population combined with foliar treatments might impact white mold incidences,” Bauer says.
Field trials were conducted in three locations in south-central Michigan, all in 15" rows. One field was irrigated and the other two had a history of white mold. A straight rate of 150,000 seeds per acre was compared with a variable rate based on the productivity of the management zone. The approach for variable rates was based on decreasing populations in highly productive zones where white mold typically thrives. Variable-rate populations ranged from 100,000 seeds per acre to 165,000. Chemical treatments included BASF’s Endura fungicide for control or suppression of white mold and Valent’s Cobra followed by Endura.
Cobra was applied at 8 oz. per acre with crop oil in the late vegetative stage. Endura was applied at 6 oz. with NIS at R2 (flowering).
In 2017, low humidity and a lack of rain did not create a favorable environment for white mold so severity was low. However, there was a reduction in the number of plants showing symptoms of white mold using a variable-rate population and fungicide, with the biggest decrease in the Cobra followed by Endura treatments.
When averaged across three locations, the systems approach using variable-rate population and a fungicide rose to the top. On average, yields increased 4.2 bu. per acre compared with the standard 150,000 population without fungicide. The fungicide increased yields by 3.3 bu. per acre in the standard population and only 1.6 bu. in the variable-rate population.
The variable-rate population helped reduce incidences of white mold so the fungicide was less important.
The most economical treatment was variable-rate population. The Cobra followed by fungicide treatment didn’t increase yields despite an improvement in pods and seeds per plant. The stress caused by the Cobra couldn’t be overcome in a low rainfall, poor vegetative growth environment.
“Population is a driving factor in white mold, so managing the disease by varying rates is a good place to start,” Bauer says.
Thank You to Our Test Plot Partners
BASF, Bayer CropScience, Pioneer, Valent, Apache, Can-Am,
Case IH, Great Plains, Kinze, New Holland, Unverferth, AirScout, Trimble, Willibey Brothers, Bob and Mary Kochendorfer, Simington Farms, Finegan Farms, North Concord Farms, Bob Miner, R&D Bracy Farms Pioneer Seed, Shipe’s Seed Service, Hoffman Ag Services and Michigan Soybean Promotion Committee
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