Timing is everything when it comes to corn and soybean fungicide applications. To that old adage agronomist Jim Schwartz adds a twist: Timing with the right class of fungicide is everything.
“To make the right fungicide selection, you must first understand the differences in fungicides. Once you understand the different classes and what they do, you’ll know when they should be applied and what you can expect them to accomplish,” says Schwartz, Director of Practical Farm Research and Agronomy for Beck’s.
class act. A good start to better understanding the different fungicide classifications is to utilize the Fungicide Classification Chart available online at https://iwilltakeaction.com/…. It lists the different classes of fungicides by the way they work. There are six classes; however, there are three major classes that corn and soybean farmers need to be aware of:
> Class 3: Cell Membrane Disrupters or DMI, often referred to as triazoles
> Class 7: Respiration Inhibitors, commonly known as SDHI
> Class 11: Respiration Inhibitors, using QOI/Strobilurins and are commonly referred to as strobis
The Class 3 triazoles are curative, notes Schwartz. They’re the fungicides you use to stop an active fungus disease problem in your field. The “strobis” and SDHI chemistries are preventative fungicides with plant health benefits.
“So, if you want to spray corn at V5 or VT and there’s no disease, but you want the benefits of ethylene suppression and prevention, spraying a triazole fungicide by itself doesn’t make as much sense,” he points out. “It might help, but will probably not give you the results you were hoping for. There you want to apply a compound that contains either or both a strobi or SDHI fungicide,” says Schwartz.
Understanding fungicide classification is also an important first step in reducing development of resistance in fungicides. To better manage resistance, “don’t spray the same triazole or strobi class fungicide every year,” advises Schwartz.
He also recommends moving to the newer pyramided compounds that incorporate these three major classes (3, 7 and 11). They help manage resistance and are effective at applying curative, preventative and plant health in one application.
FUNGICIDE ROI. What’s the return on investment (ROI) for applying fungicide on corn and soybeans? “An application can save 18 to 25 Bu./A in corn in the presence of heavy disease, such as a late outbreak of rust,” says Schwartz.
But is there a positive ROI for routine fungicide applications on corn and soybeans? Beck’s Practical Farm Research (PFR)® studies have found that timing makes a big difference. “In soybeans we’ve observed a dramatic ROI increase when applying at the R3 growth stage (pods developing on lower nodes),” notes Schwartz. Over three years, PFR research has found that the breakeven soybean price for a R3 application is around $5.75/Bu. With R2 applications, the breakeven point was much higher at $11.49/Bu. For R4 applications, it was $10.91/Bu. These results were from years when disease pressure ratings were moderate to low, says Schwartz.
Beck’s PFR team also conducted studies comparing fungicide applications (with groups 3, 7 and 11) at V5, at VT, and at V5 + VT. “Our data clearly showed that the VT (tasseling) application delivered the best ROI, with a $20/A return on investment,” says Schwartz. “The V5 + VT gave a distant $2.48/A return, while the V5 alone ended up with a negative -$3.50 ROI.”
Beck’s PFR team also observed a yield and ROI boost from increasing the carrier rate for fungicide applications on corn. “Increasing the amount of carrier water from 10 to 15 gal./A increased yield 2.2 Bu./A in our studies,” says Schwartz. He credits better spray coverage from the additional carrier water for the increased yield.
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