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3 keys to know when to pull the trigger and apply fungicides on corn3 keys to know when to pull the trigger and apply fungicides on corn

Pinpoint when you would apply fungicides during tasseling and pollination.

Tom Bechman 1

May 26, 2016

3 Min Read

Your ag supplier may already be asking you about which cornfields you want to spray with fungicide this summer. From his side of the fence, he has product to order and custom applicators to line up to hit what is always a very narrow window for fungicide application.  Agronomists recommend staying on your side of the fence, and making decisions about fungicide use and timing of potential applications that make economic sense for you.


A panel of three Indiana Certified Crop Advisers points to three keys for making decisions about fungicide applications. They are Jamie Bultemeier, Great Lakes A&L Labs, Fort Wayne; Gene Flaningam, Flaningam Ag Consulting LLC, Vincennes; and Bryan Overstreet, Purdue University Extension ag educator in Jasper County.  

1. Assess the need to spray fungicide in the first place.

“I would scout the field before making an application to see if the disease you are spraying for is even present,” Overstreet says. “And if it is present, are disease levels severe enough to warrant a fungicide application?”

Overstreet refers farmers he advises to a publication prepared by Purdue Extension. It’s called Fungicide Efficacy for Control of Corn Diseases. Find it at extension.purdue.edu/extmedia/BP/BP-160-W.pdf.

3 keys to know when to pull the trigger and apply fungicides on corn

DETERMINE DISEASE LEVEL: Here is the tricky part of making fungicide decisions. If this is the only lesion you've found and pollination is approaching, check more closely with your seed rep and weatherman.

2. Hit a narrow window for best results.

Research shows the most consistent and beneficial time to apply foliar fungicides in corn is from VT, or tasseling, to R2, after silks turn brown, Bultemeier says. In 2015, Kiersten Wise, Purdue Extension plant pathologist, announced field results indicating that to achieve the most benefit, fungicides should be applied before silks turn brown.

“The thought behind waiting to apply the fungicide has been to protect the plant longer into the grain-fill period,” Bultemeier explains. However, he notes that this philosophy has a few challenges.

“The VT-to-R2 window can be rather narrow; waiting on brown silks can dramatically decrease your window of application,” he says. “Yield benefits really decrease if application is made after R2.”

3 keys to know when to pull the trigger and apply fungicides on corn

MISSED THE WINDOW: Once brown silks dominate the field, most agronomists agree you’ve missed the window to gain maximum benefits from a fungicide application.

3. Refer to the product's label before making a final decision on application timing.

If scouting the field to see if you even need a fungicide is the first key, and aiming for a narrow window is second, then the third key is surely checking product labels carefully, Flaningam says. “The primary application timing of each fungicide will be determined by the product label,” he says.

One reason for checking labels is to find out if there are restrictions on the back end of the season, he notes. Some products have harvest restrictions after application. The range is wide, running from seven to 36 days, Flaningam notes. You can only find that information by checking fungicide labels.

Timing could depend on severity of the disease, Flaningam says. He suggests scouting regularly, and talking to your seed sales rep in advance to get a better handle on the resistance or susceptibility of each hybrid to various diseases.

“Weather predictions during grain fill could also be a factor,” he says. “Wet, cloudy weather speeds up disease development.”

3 keys to know when to pull the trigger and apply fungicides on corn

WEATHER CONDITIONS MATTER: Depending upon the disease, high humidity, lots of early morning dews like this one and cloudy conditions may favor foliar diseases.

About the Author(s)

Tom Bechman 1

Editor, Indiana Prairie Farm

Tom Bechman is an important cog in the Farm Progress machinery. In addition to serving as editor of Indiana Prairie Farmer, Tom is nationally known for his coverage of Midwest agronomy, conservation, no-till farming, farm management, farm safety, high-tech farming and personal property tax relief. His byline appears monthly in many of the 18 state and regional farm magazines published by Farm Progress.

"I consider it my responsibility and opportunity as a farm magazine editor to supply useful information that will help today's farm families survive and thrive," the veteran editor says.

Tom graduated from Whiteland (Ind.) High School, earned his B.S. in animal science and agricultural education from Purdue University in 1975 and an M.S. in dairy nutrition two years later. He first joined the magazine as a field editor in 1981 after four years as a vocational agriculture teacher.

Tom enjoys interacting with farm families, university specialists and industry leaders, gathering and sifting through loads of information available in agriculture today. "Whenever I find a new idea or a new thought that could either improve someone's life or their income, I consider it a personal challenge to discover how to present it in the most useful form, " he says.

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