With the dry conditions we are experiencing this year in much of Wisconsin (and beyond), securing enough feed becomes a concern and top priority for dairy farmers and livestock producers. As farmers consider diverting portions of their grain crops into feed crops, it’s important that they consider and respect the preharvest intervals for all crop protection products applied to their crops during the growing season.
The preharvest interval (PHI) is the minimum amount of time between the application of a crop protection product (i.e., herbicide, fungicide, insecticide) and when the treated crop can be legally harvested for forage/grazing or for grain. The U.S. Environmental Protection Agency (US EPA) has set limits on the residue levels (“tolerances”) of registered crop protection products for each labeled crop and the PHIs are in place to help meet these safety standards thus reduce the risk of animal and/or human dietary exposure. The PHI information is available on the product label, typically under “Restrictions”. Note that the PHI may or may not be the same for forage/grazing and for grain harvest. See below for examples of the PHI information found on the label of common corn herbicides:
DiFlexx herbicide (dicamba, Group 4): “Corn forage may not be harvested within 45 days of the final DIFLEXX Herbicide application. Corn grain and stover may be harvested once the crop has reached the ensilage (milk) stage.”
Status herbicide (dicamba+ diflufenzopyr, Groups 4 and 19): “DO NOT apply within 32 days before corn forage harvest” and “DO NOT apply within 72 days before popcorn, corn grain and stover harvest.”
Aatrex 4L herbicide (atrazine, Group 5): “Note for all applications to corn: Do not graze or feed forage from treated areas for 60 days following application, or illegal residues may result. For sweet corn, do not graze or feed forage from treated areas for 45 days following application, or illegal residues may result.”
Roundup PowerMAX3 herbicide (glyphosate, Group 9): “Allow a minimum of 50 days between application of this product and harvest of corn forage or grain” and ”Allow a minimum of 7 days between application and harvest or feeding of corn stover or grain.”
Dual II Magnum herbicide (S-metolachlor, Group 15): “DO NOT graze or feed forage for 30 days following application.”
Callisto herbicide (mesotrione, Group 27): “Do not harvest forage, grain, or stover within 45 days after application.”
For additional information, please check: A3646 Pest Management in Wisconsin Field Crops. Always check the product label. The label is the law.
This article was written by Dr. Rodrigo Werle, Associate Professor and Extension Cropping Systems Weed Scientist at the University of Wisconsin-Madison.