The Fungicide Factor 

March 22, 2013 08:50 PM
The Fungicide Factor 

Evaluate applications in corn that provide a return on investment

Conventional wisdom says fungicide use in corn during a drought makes little to no sense. Some plant health experts and farmers believe otherwise.

Scott Rahn chose to use a fungicide in his corn last summer despite dry conditions on his Minnesota farm.

"We were spraying a fungicide by plane over the corn and the neighbor said, ‘All you’re doing is saving the insurance company some money.’ But no, you have to give that crop a chance; if you plan for failure that’s what you’re going to get.  The crop ended up better than we thought and we beat our yield goal," says Rahn, who farms near Bingham Lake, Minn.

Other farmers saw a similar pattern of success with fungicide use in their corn crops this past year, notes Randy Myers, Bayer CropScience fungicide product manager.

"Even as adverse as conditions were in many parts of the country, if the corn pollinated and a small amount of moisture was present, we found that fungicides still protected the crop and improved yields," Myers says.

The payoff in drought conditions occurs because fungicides help keep plant stomata—microscopic pores on plant leaves that allow the exchange of gases and water—from closing, explains Jennifer Holland, BASF technical market specialist. She says when stomata close, corn plants heat up and photosynthesis declines.

"It’s like rolling up the windows in your car on a hot day," she says. "Fungicides roll down the car windows on the plant, so to speak, and help mitigate environmental stresses."

Reasons to spray. Fewer stresses means plants grow more efficiently and longer, which increases yield, she adds.

However, Holland says a fungicide cannot undo plant tissue damage that occurred prior to its application. 

Rahn describes fungicide use as an important risk-management tool and yield enhancer. He attributes its use to providing an extra 10 bu. to 20 bu. of corn per acre, on average.

Kiersten Wise, Extension plant pathologist at Purdue University, says fungicides provide a return on investment most often when conditions favor fungal disease development, typically moist, humid conditions, and not dry, hot weather.

She encourages corn growers to weigh the cost of fungicide treatments, often $24 to $35 per acre, against the price of corn to determine whether an application makes sense. Her general rule is that growers need a yield increase of about 6 bu. per acre to recover their investment.

Optimum application timing is also important to consider, adds Mark Jeschke, DuPont Pioneer agronomy research manager. His research shows the ideal application timing in corn is between tasseling (VT) and brown silk (R2). In 475 on-farm comparisons between 2007 and 2011, he says a positive yield response was observed 80% of the time. The average yield response was 7 bu. per acre.

Recently, Jeschke says manufacturers have been promoting early season fungicide applications, at V5 to V7, to provide additional yield potential. Tank mixing with a post-emergence herbicide allows the fungicide to be sprayed then without additional application costs. While that practice can reduce break-even costs, he says farmers need to evaluate whether the yield results justify the expense.

Myers says some of the value farmers can gain from fungicide use is often lost because they take a reactionary approach to applications, which ends up muting benefits. He recommends farmers take a proactive, planned approach to fungicide use.

"If you go out in the field and scout and think you need to spray, you need to spray now," he says. "With fungicides, application timeliness is very important for good performance."


You can e-mail Rhonda Brooks at

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