Mid-Atlantic wheat growers aren’t likely to get any economic benefit by applying fungicides to wheat fields that aren’t infected with fungal diseases.

That’s the conclusion of scientists based at North Carolina State University who conducted the first peer-reviewed study of its kind on calendar-based application of fungicides in wheat.

The scientists reviewed 42 publicly sponsored tests of strobilurin- and triazole-containing fungicides on soft red winter wheat in experimental plots in North Carolina and Virginia from 1994 to 2010. To reach their conclusions, they considered observed yield differences, grain prices and the cost of applying fungicides.

They found that while the fungicides make economic sense when fungal disease is present, they don’t if there’s no disease.

The scientists’ review was made public earlier this month through the journal Phytopathology’s website at 
http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-10-0096.

“It has been suggested that fungicides containing strobilurins enhance plant health and increase yield even when fungal diseases are not present and thus should be applied routinely to all wheat fields,” said one of the study’s authors, Christina Cowger. “The results of this analysis point in a different direction.”

In fields without disease, even at the highest grain price and the lowest total application cost, the average yield increase found when strobilurin was applied was not high enough to pay for an application of the fungicide, the scientists reported.

On the other hand, when fungicides are applied to combat detected disease, “fungicide application is likely to be profitable,” said Cowger, a plant pathologist with the U.S. Department of Agriculture’s Agricultural Research Service who is stationed at North Caolina State. “This result underscores the value of scouting for disease and using published disease thresholds to decide whether to spray rather than simply spraying on a calendar basis.”

Although earlier research on soybeans and sugar beets found no yield benefit to fungicides in the absence of disease, up until now there were no peer-reviewed studies of the issue in wheat, Cowger said.

The authors said it’s possible that fungicide effects could be different in commercial fields than in the experimental plots from which the study data were derived. Nevertheless, their data analysis points to the conclusion that “fungicide application to soft red winter wheat in no-disease environments will rarely be economical.”

In addition to Cowger, other study authors are Randy Weisz, North Carolina State professor of crop science and North Carolina Cooperative Extension small grains specialist; Gaylon Ambrose, Extension agriculture agent in Beaufort County; and Andrew Gardner, Extension agriculture agent in Union County.