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Will It Pay To Apply Foliar Fungicide On Corn?Will It Pay To Apply Foliar Fungicide On Corn?

With high grain prices, it may appear worth the risk to go ahead and spray. But fungicide decisions should be based on more than just the price of grain, say ISU specialists.

Rod Swoboda 1

July 21, 2011

3 Min Read

It never ceases to amaze people just how quickly corn grows. It does not seem that long ago that the corn was knee-high and now crops are 12 feet tall. Across the state, crops are flowering and pollination is underway. With tassels, comes the question: Should I spray a foliar fungicide? 


University and industry data continue to report mean yield responses due to a fungicide application that vary from 4 bushel to as much as 15 bushels per acre. With grain prices as high as they are, it may appear to be worth risk to spray, but fungicide decisions should be based on more than just the price of grain, say Iowa State University Extension plant disease specialists Alison Robertson and Daren Mueller. 

Four years of fungicide trials in Iowa and across the Corn Belt at numerous universities has clearly shown that yield responses are greater when disease is present in the field (see table 1). The data in the table shows the disease severity at R5 (dent) stage of corn, and the mean yield response that occurred when disease severity on the ear leaf was low (less than 5%) and when more than 5% of the ear leaf was diseased. 

How much disease should be present at tasseling to justify applying fungicide?

But the key question is how much disease should be present at tasseling? "Good question and one we are working on," says ISU's Alison Robertson. Fungicide trials to establish thresholds for applying a fungicide are in progress in Iowa, Illinois, Wisconsin and Ohio. This work is being funded by a grant from the USDA RAMP (Risk Avoidance and Mitigation Program) program.

For now though, the threshold remains that you should consider a fungicide application if fungal disease is present on the third leaf below the ear leaf or higher on 50% of the plants at tasseling time, and if the hybrid is susceptible to the disease, says Robertson. If the hybrid is moderately susceptible, you should consider other risk factors for disease development such as current and predicted weather conditions during grain fill, disease history of the field and previous crop. If the hybrid has good genetic resistance or tolerance to the disease, no application is needed. Following these guidelines should lead to a greater response to fungicide application due to disease pressure.

How will current and forecasted weather conditions affect disease development?

"The hot, humid conditions forecasted for the next week to 10 days will slow development of eyespot, common rust and northern leaf blight," she says. "High humidity favors gray leaf spot (GLS) sporulation and infection. Temperatures in the mid 80s favor GLS development and lesion expansion, but temperatures in the mid 90s slow disease development."

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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