If you’ve gotten into the habit of using foliar fungicides in corn simply to boost plant health and yields, you may want to reconsider. Research by Midwest university crop specialists confirms disease risk conditions should be the overriding reason to evaluate the costs and benefits associated with any corn fungicide applications.

“Since 2006, claims of substantial yield increase in response to fungicides, even in the absence of foliar disease symptoms, have led to millions of dollars of fungicide applications on millions of acres,” says Pierce Paul, plant pathologist, Ohio State University. “In 2009, the EPA granted a supplemental label for Headline for disease control and its ‘plant health’ benefit, which may have led to more widespread use without regard to disease risk.”

Paul uses statistical and computer models to describe plant disease dynamics in the field and to base disease management decisions on risk assessment and disease predictions. He says farmers most likely to benefit from using a fungicide are those planting disease-susceptible hybrids into minimum-till, corn-after-corn settings in wet, humid weather.

Paul and his colleagues performed a cost-benefit analysis of 212 replicated foliar fungicide trials in 14 states between 2002 and 2009. Corn yield response was analyzed with four of the most widely used foliar fungicides: Headline, Quadris, Quilt and Stratego. The most predominant disease pressure was gray leaf spot, but northern corn leaf blight, rusts and eyespot also were concerns. A range of grain prices and fungicide application costs was used to show how profitability of fungicide use varies with disease levels and baseline yield potential.

“Yield responses to foliar fungicides are highly variable from field to field and from year to year,” he says. “With such variability, if data from trials are not analyzed correctly, we can see erroneous conclusions about the true value and economic benefit of using a foliar fungicide.”

Researchers concluded the use of these foliar fungicides was unlikely to be profitable when foliar disease severity is low and yield expectation is high, Paul says. He says even at the highest corn price used ($7/bu.) and lowest fungicide application cost ($16.20/acre), there was a 25%, 44%, 41% and 65% chance of the yield increase being insufficient to cover the cost of applying Headline, Stratego, Quilt and Quadris respectively, when disease severity was low.

“We cannot recommend fungicides for general use when disease risk is low,” Paul says. “Fungicides may be warranted and cost effective when disease severity is greater than 5% without the use of a fungicide, grain prices are very high, application costs are low and there is reasonable knowledge that yield would be low without treatment. However, there is great uncertainty – even when disease severity is greater than 5% – that a farmer would realize a profit in any given year and location when fungicide is applied between tasseling and silking.”