Pre-harvest Restrictions for Fungicides

August 24, 2008
ICM News

By Daren Mueller, Department of Plant Pathology

With the buzz of airplanes still being heard out in the countryside and September within sight, this is just a quick reminder to growers about the pre-harvest intervals (PHI) for fungicides applied to corn and soybean. Last month in Kansas, some wheat was embargoed when fungicide levels were questioned until tests could be completed to determine residue levels.

Pre-harvest Interval (PHI) is the minimum amount of time that must pass between the last pesticide application and the harvesting of the crop, or the grazing or cutting of the crop for livestock feed. Typically, PHIs for fungicides applied to field crops range between 21-30 days.

Some triazoles and triazole + QoI fungicides have restrictions based on growth stages instead of a specific number of days; fungicides cannot be applied later than soybean growth stage R5 for soybean or after silking for corn. 


Daren Mueller is an extension specialist with responsibilities in the Corn and Soybean Initiative.



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Daren Mueller Professor

Daren Mueller is an associate professor and extension plant pathologist at Iowa State University. He is also the coordinator of the Iowa State Integrated Pest Management (IPM) program. Daren received his bachelor's degree from the University of Wisconsin-Madison in 1996, and his master's degree a...