Applying fungicides as a plant health benefit, in the absence of disease or under low disease pressures, is not a practice recommended by Ohio State University researchers.

Despite some claims that fungicides can boost corn yields, preliminary university research has found no consistent link between fungicide applications and an increase in yields when disease pressures are low, says Pierce Paul, a plant pathologist with the Ohio Agricultural Research and Development Center in Wooster.

Over one growing season, center researchers tested six hybrids with various levels of resistance to gray leaf spot and northern corn leaf blight at two Ohio locations: Apple Creek and South Charleston.

Half of the trials were sprayed with a fungicide and the other half were left untreated. Researchers compared disease levels and yield responses. With disease levels low—no higher than 12 percent for gray leaf spot and 6 percent for northern corn leaf blight—researchers found no differences in yield to fungicide applications between treated and untreated hybrids.

"Because of the data, we continue to recommend an integrated pest management (IPM) approach to managing foliar diseases of corn," Paul says. 

Paul recommends that growers scout their cornfields for foliar diseases, specifically gray leaf spot and northern corn leaf blight, and apply foliar fungicides only if necessary.

Both diseases can affect susceptible hybrids as they enter pollination and grain fill during wet periods.

"Given the dry conditions, however, little if any disease is present and fungicide applications may not be needed," Paul says. "Surveys from across the state indicate that it is a very low disease year for corn.

"For example, after gray leaf spot is first observed on the lower leaves of a susceptible hybrid, it takes 14 to 21 days or even longer under dry conditions for it to develop to the extent that it can impact yields. Given the current stage of the corn crop, the crop will already be at maturity, and by then, the disease won't even be an issue."