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Wait to Harvest: Observe Your Pre-Harvest Interval

20:14PM Sep 30, 2008
You know those PHI numbers as well as you know your own birthday. Just in case you've
forgotten, the number of days you must wait before crops can be safely harvested—the pre-harvest interval (PHI)—is stated on the pesticide label. What you might not realize is there are severe penalties if you fail to observe that waiting period.
Late season insecticide treatments represent some of the longest withdrawal times. Roy Boykin, Syngenta technical brand manager for insecticides, says the purpose of the pre-harvest interval is to ensure the insecticide residue within a crop is reduced to a safe level before entering the food system.
If farmers fail to follow a pesticide's pre-harvest interval their crop could be condemned. "This shouldn't happen if farmers follow the pre-harvest regulations on the insecticides' label,” he says.
The Environmental Protection Agency (EPA) sets the tolerance for the residue level allowed. EPA can hold farmers liable if they haul crops with unsafe pesticide residue to grain elevators.
Marlin Rice, Iowa State University entomologist, recently published an article on the legal responsibilities of farmers concerning pre-harvest intervals. To avoid violating the insecticide requirements, Rice suggests that farmers keep a record for each field, including:
  • the insecticide name and rate
  • application date
  • pre-harvest interval
  • harvest date
Rice also says custom applicators should document that they informed the farmer of the application date and pre-harvest interval for the chemical.
For More Information
For a list of common soybean insecticides and their pre-harvest intervals:
For information on some of the legal issues surrounding pre-harvest intervals: