Fungicide Checklist

July 28, 2008 07:57 AM
Sara Muri, AgWeb Crops Online Editor
Applying fungicides to your cornfields has a strong chance of preventing yield losses from fungal diseases. But, you want to make sure you're application equals dollars at harvest time. Read the following advice from three university experts, to make sure your fungicide decisions are in check.
Acknowledge the Warning Signs
Unfortunately, the deck is stacked for foliar diseases this year. Don Hershman, extension plant pathologist at the University of Kentucky, says the following factors increase risk for corn foliar diseases:
         Susceptible hybrid
         Continuous corn
         Late planting
         High yield potential
         Disease activity at tasseling
         Disease-favorable weather
         Field history of disease
Consider Your Fungicide Options
Daren Mueller, of the Iowa State University's Department of Plant Pathology, says there are two basic types of fungicides: strobilurins and triazoles.
Strobilurins are preventative fungicides that should be applied prior to infection.
Triazols are curative fungicides. "Triazols don't necessarily cure the plant, they just stop early infection,” Mueller says.
He says the triazol version is active in fighting fungal disease during the latent period, or the time between the spore entering the leaf and the infection occurring. "In my opinion there is not a large value in having the curative fungicides, due to the small window to be effective,” Mueller says.
Overall, fungicides only control diseases, Mueller says. "They will not gain yield.”
Know Your Enemy
Carl Bradley, assistant professor at the University of Illinois at Urbana-Champaign's Department of Crop Sciences, says the two main diseases that will likely cause problems this year are grey leaf spot and common rust. He says common rust may show up earlier this year on the late-planted fields.
With this year's intense weather conditions, Mueller says uncommon diseases are showing up. He says to check with your fungicide dealer or local extension specialists to confirm you are treating the right disease.
Make Sure Your Application Decisions are Field-Specific
"Farmers need to pick the fungicide that will be the most effective on the diseases present in a field,” Mueller says.
Some fields are at higher risk for fungal diseases, Bradley says. He says corn-on-corn fields have an increased risk because the fungi can overwinter on the corn stubble.
Yet, in some cases, fungicide applications may not be needed. "For resistant hybrids, it is questionable if farmers should spray at all,” says Hershman. "You will never know 100% if you should spray.”
Leave a Check Strip
All of the researchers agree farmers should leave a check strip of untreated corn when applying fungicides.
Bradley says the check strip should be in a representative part of the field and be at least as wide as the combine, for the best results. Then, farmers can get an accurate yield comparison to the rest of the field. He suggests working with your applicator to make sure a check strip is left.
By being able to compare the fungicide-treated area with a non-fungicide-treated area, you can ensure any yield differences are due to the application and not just good growing conditions. "No one wants to waste money,” Hershman says.
Address the Application Risks
Depending on your location and applicator, you may not have many options in scheduling your fungicide applications. Mueller says, if possible, don't apply them in the heat of the day. He says the fungicide could have a toxic effect in hot, sunny conditions.
Hershman says there are concerns about over-applying fungicides. "A lot of fungi keep insects under control,” he says. Therefore, continuous spraying of fungicides could kill some of the helpful stains of fungi.
"There was really no considerable spraying before 2006,” Hershman says. "This is all brand-new stuff. Farmers are using it before researchers have really studied it, creating a lot of unknowns.”
Bottom Line: Bradley says farmers should lay out all the risk factors and then make their application decisions.
For More Information

You can e-mail Sara Muri at


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